@c DO NOT EDIT!  Generated automatically by munge-texi.pl.

@c Copyright (C) 1996-2026 The Octave Project Developers
@c
@c This file is part of Octave.
@c
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@c under the terms of the GNU General Public License as published by
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@c (at your option) any later version.
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@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
@c GNU General Public License for more details.
@c
@c You should have received a copy of the GNU General Public License
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@c <https://www.gnu.org/licenses/>.

@node Input and Output
@chapter Input and Output

Octave supports several ways of reading and writing data to or from the
prompt or a file.  The simplest functions for data Input and Output
(I/O) are easy to use, but only provide limited control of how
data is processed.  For more control, a set of functions modeled
after the C standard library are also provided by Octave.

@menu
* Basic Input and Output::
* C-Style I/O Functions::
@end menu

@node Basic Input and Output
@section Basic Input and Output

@c We could use a two-line introduction here...

@menu
* Terminal Output::
* Terminal Input::
* Simple File I/O::
@end menu

@node Terminal Output
@subsection Terminal Output

Since Octave normally prints the value of an expression as soon as it
has been evaluated, the simplest of all I/O functions is a simple
expression.  For example, the following expression will display the
value of @samp{pi}

@example
@group
pi
     @print{} ans =  3.1416
@end group
@end example

This works well as long as it is acceptable to have the name of the
variable (or @samp{ans}) printed along with the value.  To print the
value of a variable without printing its name, use the function
@code{disp}.

The @code{format} command offers some control over the way Octave prints
values with @code{disp} and through the normal echoing mechanism.

@c disp libinterp/corefcn/pr-output.cc
@anchor{XREFdisp}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} disp (@var{x})
@deftypefnx {} {@var{str} =} disp (@var{x})
Display the value of @var{x}.

For example:

@example
@group
disp ("The value of pi is:"), disp (pi)

     @print{} the value of pi is:
     @print{} 3.1416
@end group
@end example

@noindent
Note that the output from @code{disp} always ends with a newline.

If an output value is requested, @code{disp} prints nothing and returns the
formatted output in a string.
@xseealso{@ref{XREFfdisp,,fdisp}}
@end deftypefn


@c list_in_columns libinterp/corefcn/strfns.cc
@anchor{XREFlist_in_columns}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{str} =} list_in_columns (@var{arg}, @var{width}, @var{prefix})
Return a string containing the elements of @var{arg} listed in columns with
an overall maximum width of @var{width} and optional prefix @var{prefix}.

The argument @var{arg} must be a cell array of character strings or a
character array.

If @var{width} is not specified or is an empty matrix, or less than or equal
to zero, the width of the terminal screen is used.  Newline characters are
used to break the lines in the output string.  For example:
@c Set example in small font to prevent overfull line

@smallexample
@group
list_in_columns (@{"abc", "def", "ghijkl", "mnop", "qrs", "tuv"@}, 20)
     @xresult{} abc     mnop
        def     qrs
        ghijkl  tuv

whos ans
     @xresult{}
     Variables in the current scope:

       Attr Name        Size                     Bytes  Class
       ==== ====        ====                     =====  =====
            ans         1x37                        37  char

     Total is 37 elements using 37 bytes
@end group
@end smallexample

@xseealso{@ref{XREFterminal_size,,terminal_size}}
@end deftypefn


@c terminal_size libinterp/corefcn/pager.cc
@anchor{XREFterminal_size}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {[@var{rows}, @var{cols}] =} terminal_size ()
@deftypefnx {} {} terminal_size ([@var{rows}, @var{cols}])
Query or set the size of the terminal window.  If called with no arguments,
return a two-element row vector containing the current size of the terminal
window in characters (rows and columns).  If called with a two-element vector
of integer values, set the terminal size and return the previous setting.
Setting the size manually should not be needed when using readline for
command-line editing.
@xseealso{@ref{XREFlist_in_columns,,list_in_columns}}
@end deftypefn


@c format libinterp/corefcn/pr-output.cc
@anchor{XREFformat}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} format
@deftypefnx {} {} format options
@deftypefnx {} {} format (@var{options})
@deftypefnx {} {[@var{format}, @var{formatspacing}, @var{uppercase}] =} format
Reset or specify the format of the output produced by @code{disp} and Octave's
normal echoing mechanism.

This command only affects the display of numbers, not how they are stored
or computed.  To change the internal representation from the default double use
one of the conversion functions such as @code{single}, @code{uint8},
@code{int64}, etc.  Any @code{format} options that change the number of
displayed significant digits will also be reflected by the
@code{output_precision} function.

By default, Octave displays 5 significant digits in a human readable form
(option @samp{short}, option @samp{lowercase}, and option @samp{loose} format
for matrices).  If @code{format} is invoked without any options, or the option
@samp{default} is specified, then this default format is restored.

Valid format options for floating point numbers are listed in the following
table.

@table @code
@item default
Restore the default format state described above.

@item short
Fixed point format with 5 significant figures (default).

@item long
Fixed point format with 16 significant figures.

As with the @samp{short} format, Octave will switch to an exponential @samp{e}
format if it is unable to format a matrix properly using the current format.

@item  shorte
@itemx longe
Exponential format.  The number to be represented is split between a mantissa
and an exponent (power of 10).  The mantissa has 5 significant digits in the
short format.  In the long format, double values are displayed with 16
significant digits and single values are displayed with 8.  For example,
with the @samp{shorte} format, @code{pi} is displayed as @code{3.1416e+00}.
Optionally, the trailing @samp{e} can be split into a second argument.

@item  shortg
@itemx longg
Optimally choose between fixed point and exponential format based on the
magnitude of the number.  For example, with the @samp{shortg} format,
@w{@code{pi .^ [2; 4; 8; 16; 32]}} is displayed as

@example
@group
ans =

      9.8696
      97.409
      9488.5
  9.0032e+07
  8.1058e+15
@end group
@end example

Optionally, the trailing @samp{g} can be split into a second argument.

@item  shorteng
@itemx longeng
Identical to @samp{shorte} or @samp{longe} but displays the value using an
engineering format, where the exponent is divisible by 3.  For example, with
the @samp{shorteng} format, @code{10 * pi} is displayed as @code{31.416e+00}.
Optionally, the trailing @samp{eng} can be split into a second argument.

@item  free
@itemx none
Print output in free format, without trying to line up columns of matrices on
the decimal point.  This is a raw format equivalent to the C++ code
@code{std::cout << @var{variable}}.  In general, the result is a presentation
with 6 significant digits where unnecessary precision (such as trailing zeros
for integers) is suppressed.  Complex numbers are formatted as numeric pairs
like this @code{(0.60419, 0.60709)} instead of like this
@code{0.60419 + 0.60709i}.
@end table

The following formats affect all numeric output (floating point and integer
types).

@table @asis
@item  @qcode{"+"}
@itemx @qcode{"+"} @qcode{"@var{chars}"}
@itemx @code{plus}
@itemx @code{plus @var{chars}}
Print a @samp{+} symbol for matrix elements greater than zero, a @samp{-}
symbol for elements less than zero, and a space for zero matrix elements.  This
format can be useful for examining the sparsity structure of a large matrix.
For very large matrices the function @code{spy} which plots the sparsity
pattern will be clearer.

The optional argument @var{chars} specifies a list of 3 characters to use for
printing values greater than zero, less than zero, and equal to zero.  For
example, with the format @qcode{"+" "+-."}, the matrix
@code{[1, 0, -1; -1, 0, 1]} is displayed as

@example
@group
ans =

+.-
-.+
@end group
@end example

@end table

@table @code
@item bank
Print variable in a format appropriate for a currency (fixed format with two
digits to the right of the decimal point).  Only the real part of a variable is
displayed, as the imaginary part makes no sense for a currency.

@item bit
Print the bit representation of numbers in memory, always with the
most significant bit first.  For example, @code{pi} is printed like this:

@smallformat
@code{0 10000000000 1001001000011111101101010100010001000010110100011000}
@end smallformat

@noindent
where spaces have been added for clarity to show the sign bit, the 11-bit
exponent, and the 52-bit mantissa, in that order.  Together they represent
@code{pi} as an IEEE@tie{}754 double precision floating point number in the
normal form.  Single precision floating point numbers are analogous.

@item native-bit
Print the bit representation of numbers as stored in memory.  For big-endian
machines, this is identical to the @code{format bit} layout seen above.
For little-endian machines, it will print the bytes in the opposite order,
though bits within a byte will still be presented with the most significant
bit on the left.

For example, the value of @code{pi} in this format on x86-64 is:

@smallformat
@code{00011000 00101101 01000100 01010100 11111011 00100001 00001001 01000000}
@end smallformat

@noindent
shown here with spaces added for clarity.  Compare with the previous bit string
from @code{format bit} to see the grouping into bytes and their ordering.

@item hex
The same as @code{format bit} above, except that bits are grouped four at a
time into hexadecimal digits for brevity.  Thus @code{pi} is represented as:

@example
400921fb54442d18
@end example

@item native-hex
The same as @code{format native-bit} above, except that bits are grouped four
at a time into hexadecimal digits for brevity.  Thus @code{pi} is represented
on an x86-64 as:

@example
182d4454fb210940
@end example

@item rat
Print a rational approximation, i.e., values are approximated as the ratio of
small integers.  For example, with the @samp{rat} format, @code{pi} is
displayed as @code{355/113}.
@end table

The following two options affect the display of scientific and hex notations.

@table @code
@item lowercase (default)
Use a lowercase @samp{e} for the exponent character in scientific notation and
lowercase @samp{a-f} for the hex digits representing 10-15.

@item uppercase
Use an uppercase @samp{E} for the exponent character in scientific notation and
uppercase @samp{A-F} for the hex digits representing 10-15.
@end table

The following two options affect the display of all matrices.

@table @code
@item compact
Remove blank lines around column number labels and between matrices producing
more compact output with more data per page.

@item loose (default)
Insert blank lines above and below column number labels and between matrices to
produce a more readable output with less data per page.
@end table

If @code{format} is called with multiple competing options, the rightmost one
is used, except for @samp{default} which will override all other options.  In
case of an error the format remains unchanged.

If called with one to three output arguments, and no inputs, return the current
format, format spacing, and uppercase preference.  Specifying both outputs and
inputs will produce an error.

@xseealso{@ref{XREFfixed_point_format,,fixed_point_format}, @ref{XREFoutput_precision,,output_precision}, @ref{XREFsplit_long_rows,,split_long_rows}, @ref{XREFprint_empty_dimensions,,print_empty_dimensions}, @ref{XREFrats,,rats}}
@end deftypefn


@menu
* Paging Screen Output::
@end menu

@node Paging Screen Output
@subsubsection Paging Screen Output

When running interactively, Octave normally sends all output directly to the
Command Window.  However, when using the CLI version of Octave this can create
a problem because large volumes of data will stream by before you can read
them.  In such cases, it is better to use a paging program such as @code{less}
or @code{more} which displays just one screenful at a time.  With @code{less}
(and some versions of @code{more}) you can also scan forward and backward, and
search for specific items.  The pager is enabled by the command @code{more on}.

Normally, no output is displayed by the pager until just before Octave is ready
to print the top level prompt, or read from the standard input (for example, by
using the @code{fscanf} or @code{scanf} functions).  This means that there may
be some delay before any output appears on your screen if you have asked Octave
to perform a significant amount of work with a single command statement.  The
function @code{fflush} may be used to force output to be sent to the pager (or
any other stream) immediately.

You can select the program to run as the pager with the @code{PAGER} function,
and configure the pager itself with the @code{PAGER_FLAGS} function.

@c more libinterp/corefcn/pager.cc
@anchor{XREFmore}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} more
@deftypefnx {} {} more on
@deftypefnx {} {} more off
Turn output pagination on or off.

Without an argument, @code{more} toggles the current state.

The current state can be determined via @code{page_screen_output}.

Using the pager is not supported on Windows in the GUI.
@xseealso{@ref{XREFpage_screen_output,,page_screen_output}, @ref{XREFpage_output_immediately,,page_output_immediately}, @ref{XREFPAGER,,PAGER}, @ref{XREFPAGER_FLAGS,,PAGER_FLAGS}}
@end deftypefn


@c PAGER libinterp/corefcn/pager.cc
@anchor{XREFPAGER}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} PAGER ()
@deftypefnx {} {@var{old_val} =} PAGER (@var{new_val})
@deftypefnx {} {@var{old_val} =} PAGER (@var{new_val}, "local")
Query or set the internal variable that specifies the program to use
to display terminal output on your system.

The default value is normally @qcode{"less"}, @qcode{"more"}, or
@qcode{"pg"}, depending on what programs are installed on your system.
@xref{Installing Octave}.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFPAGER_FLAGS,,PAGER_FLAGS}, @ref{XREFpage_output_immediately,,page_output_immediately}, @ref{XREFmore,,more}, @ref{XREFpage_screen_output,,page_screen_output}}
@end deftypefn


@c PAGER_FLAGS libinterp/corefcn/pager.cc
@anchor{XREFPAGER_FLAGS}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} PAGER_FLAGS ()
@deftypefnx {} {@var{old_val} =} PAGER_FLAGS (@var{new_val})
@deftypefnx {} {@var{old_val} =} PAGER_FLAGS (@var{new_val}, "local")
Query or set the internal variable that specifies the options to pass
to the pager.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFPAGER,,PAGER}, @ref{XREFmore,,more}, @ref{XREFpage_screen_output,,page_screen_output}, @ref{XREFpage_output_immediately,,page_output_immediately}}
@end deftypefn


@c page_screen_output libinterp/corefcn/pager.cc
@anchor{XREFpage_screen_output}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} page_screen_output ()
@deftypefnx {} {@var{old_val} =} page_screen_output (@var{new_val})
@deftypefnx {} {@var{old_val} =} page_screen_output (@var{new_val}, "local")
Query or set the internal variable that controls whether output intended
for the terminal window that is longer than one page is sent through a
pager.

This allows you to view one screenful at a time.  Some pagers
(such as @code{less}---@pxref{Installing Octave}) are also capable of moving
backward on the output.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFmore,,more}, @ref{XREFpage_output_immediately,,page_output_immediately}, @ref{XREFPAGER,,PAGER}, @ref{XREFPAGER_FLAGS,,PAGER_FLAGS}}
@end deftypefn


@c page_output_immediately libinterp/corefcn/pager.cc
@anchor{XREFpage_output_immediately}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} page_output_immediately ()
@deftypefnx {} {@var{old_val} =} page_output_immediately (@var{new_val})
@deftypefnx {} {@var{old_val} =} page_output_immediately (@var{new_val}, "local")
Query or set the internal variable that controls whether Octave sends
output to the pager as soon as it is available.

When the value is @code{false}, Octave buffers its output and waits until just
before the prompt is printed to flush it to the pager.  This is the default.

When @code{page_screen_output} is @code{false}, this variable has no effect.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFpage_screen_output,,page_screen_output}, @ref{XREFmore,,more}, @ref{XREFPAGER,,PAGER}, @ref{XREFPAGER_FLAGS,,PAGER_FLAGS}}
@end deftypefn


@c fflush libinterp/corefcn/file-io.cc
@anchor{XREFfflush}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{status} =} fflush (@var{fid})
Flush output to file descriptor @var{fid}.

@code{fflush} returns 0 on success and an OS dependent error value
(@minus{}1 on Unix) on error.

Programming Note: Flushing is useful for ensuring that all pending output
makes it to the screen before some other event occurs.  For example, it is
always a good idea to flush the standard output stream before calling
@code{input}.
@xseealso{@ref{XREFfopen,,fopen}, @ref{XREFfclose,,fclose}}
@end deftypefn


@c FIXME: maybe this would be a good place to describe the following message:
@c
@c warning: connection to external pager (pid = 9334) lost --
@c warning: pending computations and output may be lost
@c warning: broken pipe

@node Terminal Input
@subsection Terminal Input

Octave has three functions that make it easy to prompt users for
input.  The @code{input} and @code{menu} functions are normally
used for managing an interactive dialog with a user, and the
@code{keyboard} function is normally used for doing simple debugging.

@c input libinterp/corefcn/input.cc
@anchor{XREFinput}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{ans} =} input (@var{prompt})
@deftypefnx {} {@var{ans} =} input (@var{prompt}, "s")
Print @var{prompt} and wait for user input.

For example,

@example
input ("Pick a number, any number! ")
@end example

@noindent
prints the prompt

@example
Pick a number, any number!
@end example

@noindent
and waits for the user to enter a value.  The string entered by the user
is evaluated as an expression, so it may be a literal constant, a variable
name, or any other valid Octave code.

The number of return arguments, their size, and their class depend on the
expression entered.

If you are only interested in getting a literal string value, you can call
@code{input} with the character string @qcode{"s"} as the second argument.
This tells Octave to return the string entered by the user directly, without
evaluating it first.

Because there may be output waiting to be displayed by the pager, it is a
good idea to always call @code{fflush (stdout)} before calling @code{input}.
 This will ensure that all pending output is written to the screen before
your prompt.
@xseealso{@ref{XREFyes_or_no,,yes_or_no}, @ref{XREFkbhit,,kbhit}, @ref{XREFpause,,pause}, @ref{XREFmenu,,menu}, @ref{XREFlistdlg,,listdlg}}
@end deftypefn


@c menu scripts/miscellaneous/menu.m
@anchor{XREFmenu}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{choice} =} menu (@var{title}, @var{opt1}, @dots{})
@deftypefnx {} {@var{choice} =} menu (@var{title}, @{@var{opt1}, @dots{}@})
Display a menu with heading @var{title} and options @var{opt1}, @dots{},
and wait for user input.

If the GUI is running, the menu is displayed graphically using
@code{listdlg}.  Otherwise, the title and menu options are printed on the
console.

@var{title} is a string and the options may be input as individual strings
or as a cell array of strings.

The return value @var{choice} is the number of the option selected by the
user counting from 1.  If the user aborts the dialog or makes an invalid
selection then 0 is returned.

This function is useful for interactive programs.  There is no limit to the
number of options that may be passed in, but it may be confusing to present
more than will fit easily on one screen.
@xseealso{@ref{XREFinput,,input}, @ref{XREFlistdlg,,listdlg}}
@end deftypefn


@c yes_or_no libinterp/corefcn/input.cc
@anchor{XREFyes_or_no}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{ans} =} yes_or_no ("@var{prompt}")
Ask the user a yes-or-no question.

Return logical true if the answer is yes or false if the answer is no.

Takes one argument, @var{prompt}, which is the string to display when asking
the question.  @var{prompt} should end in a space; @code{yes-or-no} adds the
string @samp{(yes or no) } to it.  The user must confirm the answer with
@key{RET} and can edit it until it has been confirmed.
@xseealso{@ref{XREFinput,,input}}
@end deftypefn


For @code{input}, the normal command line history and editing functions
are available at the prompt.

Octave also has a function that makes it possible to get a single
character from the keyboard without requiring the user to type a
carriage return.

@c kbhit libinterp/corefcn/sysdep.cc
@anchor{XREFkbhit}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{c} =} kbhit ()
@deftypefnx {} {@var{c} =} kbhit (1)
Read a single keystroke from the keyboard.

If called with an argument (typically 1), don't wait for a keypress and
immediately return the next keystroke in the keyboard input buffer or an empty
string ("") if no keystroke is available.

For example,

@example
c = kbhit ();
@end example

@noindent
will set @var{c} to the next character typed at the keyboard as soon as it is
typed.

@example
c = kbhit (1);
@end example

@noindent
is identical to the above example, but doesn't wait for a keypress, returning
the empty string if no key is available.
@xseealso{@ref{XREFinput,,input}, @ref{XREFpause,,pause}}
@end deftypefn


@node Simple File I/O
@subsection Simple File I/O

@cindex saving data
@cindex loading data
The @code{save} and @code{load} commands allow data to be written to and
read from disk files in various formats.  The default format of files
written by the @code{save} command can be controlled using the functions
@code{save_default_options} and @code{save_precision}.

As an example the following code creates a 3-by-3 matrix and saves it
to the file @samp{myfile.mat}.

@example
@group
A = [ 1:3; 4:6; 7:9 ];
save myfile.mat A
@end group
@end example

Once one or more variables have been saved to a file, they can be
read into memory using the @code{load} command.

@example
@group
load myfile.mat
A
     @print{} A =
     @print{}
     @print{}    1   2   3
     @print{}    4   5   6
     @print{}    7   8   9
@end group
@end example

@c save libinterp/corefcn/load-save.cc
@anchor{XREFsave}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} save file
@deftypefnx {} {} save options file
@deftypefnx {} {} save options file @var{v1} @var{v2} @dots{}
@deftypefnx {} {} save options file -struct @var{STRUCT}
@deftypefnx {} {} save options file -struct @var{STRUCT} @var{f1} @var{f2} @dots{}
@deftypefnx {} {} save - @var{v1} @var{v2} @dots{}
@deftypefnx {} {@var{str} =} save ("-", @qcode{"@var{v1}"}, @qcode{"@var{v2}"}, @dots{})
Save the named variables @var{v1}, @var{v2}, @dots{}, in the file @var{file}.

If no variable names are listed, Octave saves all the variables in the current
scope.  Otherwise, full variable names or pattern syntax can be used to specify
the variables to save.  If the @option{-struct} modifier is used then the
fields of the @strong{scalar} struct are saved as if they were variables with
the corresponding field names.  The @option{-struct} option can be combined
with specific field names @var{f1}, @var{f2}, @dots{} to write only certain
fields to the file.

The @code{save} command may also be invoked using the functional form

@example
save ("-option1", @dots{}, "file", "v1", @dots{})
@end example

@noindent
where the @var{options}, @var{file}, and variable name arguments (@var{v1},
@dots{}) must be specified as character strings.

Valid options for the @code{save} command are listed in the following table.
Options that modify the output format override the format specified by
@code{save_default_options}.

@table @code
@item -append
Append to the file instead of overwriting.

@item -ascii
Save a matrix in a text file without a header or any other information.  The
matrix must be 2-D and only the real part of any complex value is written to
the file.  Numbers are stored in single-precision format and separated by
spaces.  Additional options for the @option{-ascii} format are

@table @code
@item -double
Store numbers in double-precision format.

@item -tabs
Separate numbers with tabs.
@end table

@item -binary
Save the data in Octave's binary data format.

@item -float-binary
Save the data in Octave's binary data format using just single precision.
Use this format @strong{only} if you know that all the values to be saved can
be represented in single precision.

@item -hdf5
Save the data in @sc{hdf5} format.  (@sc{hdf5} is a free, portable, binary
format developed by the National Center for Supercomputing Applications at the
University of Illinois.)  This format is only available if Octave was built
with a link to the @sc{hdf5} libraries.

@item -float-hdf5
Save the data in @sc{hdf5} format using just single precision.  Use this
format @strong{only} if you know that all the values to be saved can be
represented in single precision.

@item -text (default)
Save the data in Octave's text data format.  The
@ref{XREFsave_precision,,@code{save_precision}} function specifies the number
of significant figures to use when saving data (default: 17).  The header of
the text data file can be configure with
@ref{XREFsave_header_format_string,,save_header_format_string}.

@item  -v7.3
@itemx -V7.3
@itemx -7.3
Octave does @strong{not} yet implement saving in @sc{matlab}'s v7.3 binary
data format.

@item  -v7
@itemx -V7
@itemx -7
@itemx -mat7-binary
Save the data in @sc{matlab}'s v7 binary data format.

@item  -v6
@itemx -V6
@itemx -6
@itemx -mat
@itemx -mat-binary
Save the data in @sc{matlab}'s v6 binary data format.

@item  -v4
@itemx -V4
@itemx -4
@itemx -mat4-binary
Save the data in @sc{matlab}'s v4 binary data format.

@item  -zip
@itemx -z
Use the gzip algorithm to compress the file.  This works on files that are
compressed with gzip outside of Octave, and gzip can also be used to convert
the files for backward compatibility.  This option is only available if Octave
was built with a link to the zlib libraries.
@end table

The list of variables to save may use wildcard patterns (glob patterns)
containing the following special characters:

@table @code
@item ?
Match any single character.

@item *
Match zero or more characters.

@item [ @var{list} ]
Match the list of characters specified by @var{list}.  If the first character
is @code{!} or @code{^}, match all characters except those specified by
@var{list}.  For example, the pattern @code{[a-zA-Z]} will match all lower and
uppercase alphabetic characters.

Wildcards may also be used in the field name specifications when using the
@option{-struct} modifier (but not in the struct name itself).

@end table

Programming Notes: If called with the special filename @qcode{"-"} the data to
be saved is returned as a string rather than writing it to an actual file.

When saving global variables the global status of the variable is also stored.
If the variable is restored at a later time using @code{load}, it will be
restored as a global variable.  Global status is @emph{not} preserved if
using a @sc{matlab} binary data file format or the @option{-ascii} format.

Note that @code{classdef} objects will be saved as @code{struct} in file
formats that support saving @code{struct}.  That means they will not be loaded
as @code{classdef} objects when loading the variables from the save file at a
later point.

Example:

The command

@example
save -binary data a b*
@end example

@noindent
saves the variable @samp{a} and all variables beginning with @samp{b} to the
file @file{data} in Octave's binary format.

@xseealso{@ref{XREFload,,load}, @ref{XREFsave_default_options,,save_default_options}, @ref{XREFsave_header_format_string,,save_header_format_string}, @ref{XREFsave_precision,,save_precision}, @ref{XREFcsvwrite,,csvwrite}, @ref{XREFdlmwrite,,dlmwrite}, @ref{XREFfwrite,,fwrite}}
@end deftypefn


There are three functions that modify the behavior of @code{save}.

@c save_default_options libinterp/corefcn/load-save.cc
@anchor{XREFsave_default_options}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} save_default_options ()
@deftypefnx {} {@var{old_val} =} save_default_options (@var{new_val})
@deftypefnx {} {@var{old_val} =} save_default_options (@var{new_val}, "local")
Query or set the internal variable that specifies the default options
for the @code{save} command, and defines the default format.

The default value is @qcode{"-text"} (Octave's own text-based file format).
See the documentation of the @code{save} command for other choices.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFsave,,save}, @ref{XREFsave_header_format_string,,save_header_format_string}, @ref{XREFsave_precision,,save_precision}}
@end deftypefn


@c save_precision libinterp/corefcn/ls-oct-text.cc
@anchor{XREFsave_precision}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} save_precision ()
@deftypefnx {} {@var{old_val} =} save_precision (@var{new_val})
@deftypefnx {} {@var{old_val} =} save_precision (@var{new_val}, "local")
Query or set the internal variable that specifies the number of digits to
keep when saving data in text format.

The default value is 17 which is the minimum necessary for the lossless saving
and restoring of IEEE@tie{}754 double values; For IEEE@tie{}754 single values
the minimum value is 9.  If file size is a concern, it is probably better to
choose a binary format for saving data rather than to reduce the precision of
the saved values.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.

@xseealso{@ref{XREFsave_default_options,,save_default_options}}
@end deftypefn


@c save_header_format_string libinterp/corefcn/load-save.cc
@anchor{XREFsave_header_format_string}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} save_header_format_string ()
@deftypefnx {} {@var{old_val} =} save_header_format_string (@var{new_val})
@deftypefnx {} {@var{old_val} =} save_header_format_string (@var{new_val}, "local")
Query or set the internal variable that specifies the format string used for
the comment line written at the beginning of text-format data files saved by
Octave.

The format string is passed to @code{strftime} and must begin with the
character @samp{#} and contain no newline characters.  If the value of
@code{save_header_format_string} is the empty string, the header comment is
omitted from text-format data files.  The default value is
@c Set example in small font to prevent overfull line

@smallexample
"# Created by Octave VERSION, %a %b %d %H:%M:%S %Y %Z"
@end smallexample

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFstrftime,,strftime}, @ref{XREFsave_default_options,,save_default_options}}
@end deftypefn


@c load libinterp/corefcn/load-save.cc
@anchor{XREFload}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} load file
@deftypefnx {} {} load options file
@deftypefnx {} {} load options file v1 v2 @dots{}
@deftypefnx {} {S =} load ("options", "file", "v1", "v2", @dots{})
@deftypefnx {} {} load file options
@deftypefnx {} {} load file options v1 v2 @dots{}
@deftypefnx {} {S =} load ("file", "options", "v1", "v2", @dots{})
Load the named variables @var{v1}, @var{v2}, @dots{}, from the file @var{file}.

If no variables are specified then all variables found in the file will be
loaded.  Otherwise, full variable names or pattern syntax can be used to
specify the variables to save.  The format of the file is automatically
detected but may be overridden by supplying the appropriate option.

The @code{load} command may also be invoked using the functional form

@example
load ("-option1", @dots{}, "file", "v1", @dots{})
@end example

@noindent
where the @var{options}, @var{file}, and variable name arguments (@var{v1},
@dots{}) must be specified as character strings.

Valid options for @code{load} are listed in the following table.

@table @code

@item -ascii
Force Octave to assume the file contains columns of numbers in text format
without any header or other information.  Data in the file will be loaded
as a single numeric matrix with the name of the variable derived from the
name of the file.

@item -binary
Force Octave to assume the file is in Octave's binary format.

@item -hdf5
Force Octave to assume the file is in @sc{hdf5} format.  (@sc{hdf5} is a free,
portable binary format developed by the National Center for Supercomputing
Applications at the University of Illinois.)  Note that @code{load} is only
designed to read @sc{hdf5} files that were created by Octave with @code{save},
and attempts to read other @sc{hdf5} files may fail or produce unpredictable
results.  The @option{-hdf5} option provides a limited ability to read files
created using @sc{matlab}'s @option{-v7.3} option (which saves in @sc{hdf5}
format) although many data types are not yet supported.  This format is only
available if Octave was built with a link to the @sc{hdf5} libraries.

@item -text
Force Octave to assume the file is in Octave's text format.

@item  -v7.3
@itemx -V7.3
@itemx -7.3
Octave does @strong{not} yet implement @sc{matlab}'s v7.3 binary data format.
As the v7.3 format is an @sc{hdf5} based format, the @qcode{"-hdf5"} option
may be used to attempt to open a v7.3 format file, although most non-numeric
data types are not yet supported.  Note that Octave @strong{can not} currently
save in this format.

@item  -v7
@itemx -V7
@itemx -7
@itemx -mat7-binary
Force Octave to assume the file is in @sc{matlab}'s version 7 binary format.

@item  -v6
@itemx -V6
@itemx -6
@itemx -mat
@itemx -mat-binary
Force Octave to assume the file is in @sc{matlab}'s version 6 binary format.

@item  -v4
@itemx -V4
@itemx -4
@itemx -mat4-binary
Force Octave to assume the file is in @sc{matlab}'s version 4 binary format.

@end table

The list of variables to load may use wildcard patterns (glob patterns)
containing the following special characters:

@table @code
@item ?
Match any single character.

@item *
Match zero or more characters.

@item [ @var{list} ]
Match the list of characters specified by @var{list}.  If the first character
is @code{!} or @code{^}, match all characters except those specified by
@var{list}.  For example, the pattern @code{[a-zA-Z]} will match all lower and
uppercase alphabetic characters.

@end table

If invoked with a single output argument, Octave assigns loaded data to the
output instead of inserting variables in the symbol table.  If the data file
contains only numbers (TAB- or space-delimited columns), a matrix of values is
returned.  Otherwise, @code{load} returns a structure with members
corresponding to the names of the variables in the file.

The @code{load} command can read data stored in Octave's text and binary
formats, @sc{matlab}'s binary format, and many simple formats such as
comma-separated-values (CSV).  If compiled with zlib support, it can also load
gzip-compressed files.  It will automatically detect the type of file and do
conversion from different floating point formats (currently only IEEE big and
little endian, though other formats may be added in the future).

Programming Note: If a variable that is not marked as global is loaded from a
file when a global symbol with the same name already exists, it is loaded in
the global symbol table.  Also, if a variable is marked as global in a file and
a local symbol exists, the local symbol is moved to the global symbol table and
given the value from the file.

@xseealso{@ref{XREFsave,,save}, @ref{XREFcsvread,,csvread}, @ref{XREFdlmread,,dlmread}, @ref{XREFfread,,fread}, @ref{XREFtextscan,,textscan}}
@end deftypefn


@c fileread scripts/io/fileread.m
@anchor{XREFfileread}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{str} =} fileread (@var{filename})
@deftypefnx {} {@var{str} =} fileread (@var{filename}, @var{param}, @var{value}, @dots{})
Read the contents of @var{filename} and return it as a string.

@var{param}, @var{value} are optional pairs of parameters and values.  Valid
options are:

@table @asis
@item @qcode{"Encoding"}
Specify encoding used when reading from the file.  This is a character
string of a valid encoding identifier.  The default is
@nospell{@qcode{"utf-8"}}.
@end table

@xseealso{@ref{XREFfopen,,fopen}, @ref{XREFfread,,fread}, @ref{XREFfscanf,,fscanf}, @ref{XREFimportdata,,importdata}, @ref{XREFtextscan,,textscan}, @ref{XREFtype,,type}}
@end deftypefn


@c native_float_format libinterp/corefcn/sysdep.cc
@anchor{XREFnative_float_format}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{fmtstr} =} native_float_format ()
Return the native floating point format as a string.
@end deftypefn


It is possible to write data to a file in a similar way to the
@code{disp} function for writing data to the screen.  The @code{fdisp}
works just like @code{disp} except its first argument is a file pointer
as created by @code{fopen}.  As an example, the following code writes
to data @samp{myfile.txt}.

@example
@group
fid = fopen ("myfile.txt", "w");
fdisp (fid, "3/8 is ");
fdisp (fid, 3/8);
fclose (fid);
@end group
@end example

@noindent
@xref{Opening and Closing Files}, for details on how to use @code{fopen}
and @code{fclose}.

@c fdisp libinterp/corefcn/pr-output.cc
@anchor{XREFfdisp}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {} fdisp (@var{fid}, @var{x})
Display the value of @var{x} on the stream @var{fid}.

For example:

@example
@group
fdisp (stdout, "The value of pi is:"), fdisp (stdout, pi)

     @print{} the value of pi is:
     @print{} 3.1416
@end group
@end example

@noindent
Note that the output from @code{fdisp} always ends with a newline.
@xseealso{@ref{XREFdisp,,disp}}
@end deftypefn


Octave can also read and write matrices text files such as comma
separated lists.

@c dlmwrite scripts/io/dlmwrite.m
@anchor{XREFdlmwrite}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} dlmwrite (@var{file}, @var{M})
@deftypefnx {} {} dlmwrite (@var{file}, @var{M}, @var{delim}, @var{r}, @var{c})
@deftypefnx {} {} dlmwrite (@var{file}, @var{M}, @var{key}, @var{val} @dots{})
@deftypefnx {} {} dlmwrite (@var{file}, @var{M}, "-append", @dots{})
@deftypefnx {} {} dlmwrite (@var{fid}, @dots{})
Write the numeric matrix @var{M} to the text file @var{file} using a
delimiter.

@var{file} should be a filename or a writable file ID given by @code{fopen}.

The parameter @var{delim} specifies the delimiter to use to separate values
on a row.  If no delimiter is specified the comma character @samp{,} is
used.

The value of @var{r} specifies the number of delimiter-only lines to add to
the start of the file.

The value of @var{c} specifies the number of delimiters to prepend to each
line of data.

If the argument @qcode{"-append"} is given, append to the end of @var{file}.

In addition, the following keyword value pairs may appear at the end of
the argument list:

@table @asis
@item @qcode{"append"}
Either @qcode{"on"} or @qcode{"off"}.  See @qcode{"-append"} above.

@item @qcode{"delimiter"}
See @var{delim} above.

@item @qcode{"newline"}
The character(s) to separate each row.  Three special cases exist for this
option.  @qcode{"unix"} is changed into @qcode{"@backslashchar{}n"},
@qcode{"pc"} is changed into @qcode{"@backslashchar{}r@backslashchar{}n"},
and @qcode{"mac"} is changed into @qcode{"@backslashchar{}r"}.  Any other
value is used directly as the newline separator.

@item @qcode{"roffset"}
See @var{r} above.

@item @qcode{"coffset"}
See @var{c} above.

@item @qcode{"precision"}
The precision to use when writing the file.  It can either be a format
string (as used by fprintf) or a number of significant digits.
@end table

@example
dlmwrite ("file.csv", reshape (1:16, 4, 4));
@end example

@example
dlmwrite ("file.tex", a, "delimiter", "&", "newline", "\n")
@end example

@xseealso{@ref{XREFdlmread,,dlmread}, @ref{XREFcsvread,,csvread}, @ref{XREFcsvwrite,,csvwrite}}
@end deftypefn


@c dlmread libinterp/corefcn/dlmread.cc
@anchor{XREFdlmread}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{data} =} dlmread (@var{file})
@deftypefnx {} {@var{data} =} dlmread (@var{file}, @var{sep})
@deftypefnx {} {@var{data} =} dlmread (@var{file}, @var{sep}, @var{r0}, @var{c0})
@deftypefnx {} {@var{data} =} dlmread (@var{file}, @var{sep}, @var{range})
@deftypefnx {} {@var{data} =} dlmread (@dots{}, "emptyvalue", @var{EMPTYVAL})
Read numeric data from the text file @var{file} which uses the delimiter
@var{sep} between data values.

If @var{sep} is not defined the separator between fields is determined from
the file itself.

The optional scalar arguments @var{r0} and @var{c0} define the starting row
and column of the data to be read.  These values are indexed from zero,
i.e., the first data row corresponds to an index of zero.

The @var{range} parameter specifies exactly which data elements are read.
The first form of the parameter is a 4-element vector containing the upper
left and lower right corners @code{[@var{R0},@var{C0},@var{R1},@var{C1}]}
where the indices are zero-based.  To specify the last column---the equivalent
of @code{end} when indexing---use the specifier @code{Inf}.  Alternatively, a
spreadsheet style form such as @qcode{"A2..Q15"} or @qcode{"T1:AA5"} can be
used.  The lowest alphabetical index @qcode{'A'} refers to the first column.
The lowest row index is 1.

@var{file} should be a filename or a file id given by @code{fopen}.  In the
latter case, the file is read until end of file is reached.

The @qcode{"emptyvalue"} option may be used to specify the value used to
fill empty fields.  The default is zero.  Note that any non-numeric values,
such as text, are also replaced by the @qcode{"emptyvalue"}.
@xseealso{@ref{XREFcsvread,,csvread}, @ref{XREFtextscan,,textscan}, @ref{XREFdlmwrite,,dlmwrite}}
@end deftypefn


@c csvwrite scripts/io/csvwrite.m
@anchor{XREFcsvwrite}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} csvwrite (@var{filename}, @var{x})
@deftypefnx {} {} csvwrite (@var{filename}, @var{x}, @var{dlm_opt1}, @dots{})
Write the numeric matrix @var{x} to the file @var{filename} in
@w{comma-separated-value}@ (CSV) format.

This function is equivalent to

@example
dlmwrite (@var{filename}, @var{x}, ",", @var{dlm_opt1}, @dots{})
@end example

Any optional arguments are passed directly to @code{dlmwrite}
(@pxref{XREFdlmwrite,,@code{dlmwrite}}).
@xseealso{@ref{XREFcsvread,,csvread}, @ref{XREFdlmwrite,,dlmwrite}, @ref{XREFdlmread,,dlmread}}
@end deftypefn


@c csvread scripts/io/csvread.m
@anchor{XREFcsvread}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{x} =} csvread (@var{filename})
@deftypefnx {} {@var{x} =} csvread (@var{filename}, @var{dlm_opt1}, @dots{})
Read the comma-separated-value (CSV) file @var{filename} into the matrix
@var{x}.

Note: only CSV files containing numeric data can be read.

This function is equivalent to

@example
@var{x} = dlmread (@var{filename}, "," , @var{dlm_opt1}, @dots{})
@end example

Any optional arguments are passed directly to @code{dlmread}
(@pxref{XREFdlmread,,@code{dlmread}}).
@xseealso{@ref{XREFdlmread,,dlmread}, @ref{XREFtextscan,,textscan}, @ref{XREFcsvwrite,,csvwrite}, @ref{XREFdlmwrite,,dlmwrite}}
@end deftypefn


Formatted data from can be read from, or written to, text files as well.

@c textread scripts/legacy/textread.m
@anchor{XREFtextread}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {[@var{a}, @dots{}] =} textread (@var{filename})
@deftypefnx {} {[@var{a}, @dots{}] =} textread (@var{filename}, @var{format})
@deftypefnx {} {[@var{a}, @dots{}] =} textread (@var{filename}, @var{format}, @var{n})
@deftypefnx {} {[@var{a}, @dots{}] =} textread (@var{filename}, @var{format}, @var{prop1}, @var{value1}, @dots{})
@deftypefnx {} {[@var{a}, @dots{}] =} textread (@var{filename}, @var{format}, @var{n}, @var{prop1}, @var{value1}, @dots{})

This function is obsolete.  Use @code{textscan} instead.

Read data from a text file.

The file @var{filename} is read and parsed according to @var{format}.  The
function behaves like @code{strread} except it works by parsing a file
instead of a string.  See the documentation of @code{strread} for details.

In addition to the options supported by @code{strread}, this function
supports two more:

@itemize
@item @qcode{"headerlines"}:
The first @var{value} number of lines of @var{filename} are skipped.

@item @qcode{"endofline"}:
Specify a single character or
@qcode{"@backslashchar{}r@backslashchar{}n"}.  If no value is given, it
will be inferred from the file.  If set to @qcode{""} (empty string) EOLs
are ignored as delimiters.
@end itemize

The optional input @var{n} (format repeat count) specifies the number of
times the format string is to be used or the number of lines to be read,
whichever happens first while reading.  The former is equivalent to
requesting that the data output vectors should be of length @var{N}.
Note that when reading files with format strings referring to multiple
lines, @var{n} should rather be the number of lines to be read than the
number of format string uses.

If the format string is empty (not just omitted) and the file contains only
numeric data (excluding headerlines), textread will return a rectangular
matrix with the number of columns matching the number of numeric fields on
the first data line of the file.  Empty fields are returned as zero values.

Examples:

@example
@group
  Assume a data file like:
  1 a 2 b
  3 c 4 d
  5 e
@end group
@end example

@example
@group
  [a, b] = textread (f, "%f %s")
  returns two columns of data, one with doubles, the other a
  cellstr array:
  a = [1; 2; 3; 4; 5]
  b = @{"a"; "b"; "c"; "d"; "e"@}
@end group
@end example

@example
@group
  [a, b] = textread (f, "%f %s", 3)
  (read data into two culumns, try to use the format string
  three times)
  returns
  a = [1; 2; 3]
  b = @{"a"; "b"; "c"@}

@end group
@end example

@example
@group
  With a data file like:
  1
  a
  2
  b

  [a, b] = textread (f, "%f %s", 2)
  returns a = 1 and b = @{"a"@}; i.e., the format string is used
  only once because the format string refers to 2 lines of the
  data file.  To obtain 2x1 data output columns, specify N = 4
  (number of data lines containing all requested data) rather
  than 2.
@end group
@end example

@xseealso{@ref{XREFtextscan,,textscan}, @ref{XREFload,,load}, @ref{XREFdlmread,,dlmread}, @ref{XREFfscanf,,fscanf}, @ref{XREFstrread,,strread}}
@end deftypefn


@c textscan libinterp/corefcn/file-io.cc
@anchor{XREFtextscan}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{C} =} textscan (@var{fid}, @var{format})
@deftypefnx {} {@var{C} =} textscan (@var{fid}, @var{format}, @var{repeat})
@deftypefnx {} {@var{C} =} textscan (@var{fid}, @var{format}, @var{param}, @var{value}, @dots{})
@deftypefnx {} {@var{C} =} textscan (@var{fid}, @var{format}, @var{repeat}, @var{param}, @var{value}, @dots{})
@deftypefnx {} {@var{C} =} textscan (@var{str}, @dots{})
@deftypefnx {} {[@var{C}, @var{position}, @var{errmsg}] =} textscan (@dots{})
Read data from a text file or string.

The string @var{str} or file associated with @var{fid} is read from and
parsed according to @var{format}.  The function is an extension of
@code{strread} and @code{textread}.  Differences include: the ability to
read from either a file or a string, additional options, and additional
format specifiers.

The input is interpreted as a sequence of words, delimiters (such as
whitespace), and literals.  The characters that form delimiters and
whitespace are determined by the options.  The format consists of format
specifiers interspersed between literals.  In the format, whitespace forms
a delimiter between consecutive literals, but is otherwise ignored.

The output @var{C} is a cell array where the number of columns is determined
by the number of format specifiers.

The first word of the input is matched to the first specifier of the format
and placed in the first column of the output; the second is matched to the
second specifier and placed in the second column and so forth.  If there
are more words than specifiers then the process is repeated until all words
have been processed or the limit imposed by @var{repeat} has been met (see
below).

The string @var{format} describes how the words in @var{str} should be
parsed.  As in @var{fscanf}, any (non-whitespace) text in the format that is
not one of these specifiers is considered a literal.  If there is a literal
between two format specifiers then that same literal must appear in the
input stream between the matching words.

The following specifiers are valid:

@table @code
@item  %f
@itemx %f64
@itemx %n
The word is parsed as a number and converted to double.

@item  %f32
The word is parsed as a number and converted to single (float).

@item  %d
@itemx %d8
@itemx %d16
@itemx %d32
@itemx %d64
The word is parsed as a number and converted to int8, int16, int32, or
int64.  If no size is specified then int32 is used.

@item  %u
@itemx %u8
@itemx %u16
@itemx %u32
@itemx %u64
The word is parsed as a number and converted to uint8, uint16, uint32, or
uint64.  If no size is specified then uint32 is used.

@item %s
The word is parsed as a string ending at the last character before
whitespace, an end-of-line, or a delimiter specified in the options.

@item %q
The word is parsed as a "quoted string".
If the first character of the string is a double quote (") then the string
includes everything until a matching double quote---including whitespace,
delimiters, and end-of-line characters.  If a pair of consecutive double
quotes appears in the input, it is replaced in the output by a single
double quote.  For examples, the input "He said ""Hello""" would
return the value 'He said "Hello"'.

@item  %c
The next character of the input is read.
This includes delimiters, whitespace, and end-of-line characters.

@item  %[@dots{}]
@itemx %[^@dots{}]
In the first form, the word consists of the longest run consisting of only
characters between the brackets.  Ranges of characters can be specified by
a hyphen; for example, %[0-9a-zA-Z] matches all alphanumeric characters (if
the underlying character set is ASCII).  Since @sc{matlab} treats hyphens
literally, this expansion only applies to alphanumeric characters.  To
include '-' in the set, it should appear first or last in the brackets; to
include ']', it should be the first character.  If the first character is
'^' then the word consists of characters @strong{not} listed.

@item %N@dots{}
For %s, %c %d, %f, %n, %u, an optional width can be specified as %Ns, etc.
where N is an integer > 1.  For %c, this causes exactly N characters to be
read instead of a single character.  For the other specifiers, it is an
upper bound on the number of characters read; normal delimiters can cause
fewer characters to be read.  For complex numbers, this limit applies to
the real and imaginary components individually.  For %f and %n, format
specifiers like %N.Mf are allowed, where M is an upper bound on number of
characters after the decimal point to be considered; subsequent digits are
skipped.  For example, the specifier %8.2f would read 12.345e6 as 1.234e7.

@item %*@dots{}
The word specified by the remainder of the conversion specifier is skipped.

@item literals
In addition the format may contain literal character strings; these will be
skipped during reading.  If the input string does not match this literal,
the processing terminates.
@end table

Parsed words corresponding to the first specifier are returned in the first
output argument and likewise for the rest of the specifiers.

By default, if there is only one input argument, @var{format} is @t{"%f"}.
This means that numbers are read from the input into a single column vector.
If @var{format} is explicitly empty (@qcode{""}) then textscan will
return data in a number of columns matching the number of fields on the
first data line of the input.  Either of these is suitable only when the
input is exclusively numeric.

For example, the string

@smallexample
@group
@var{str} = "\
Bunny Bugs   5.5\n\
Duck Daffy  -7.5e-5\n\
Penguin Tux   6"
@end group
@end smallexample

@noindent
can be read using

@example
@var{a} = textscan (@var{str}, "%s %s %f");
@end example

The optional numeric argument @var{repeat} can be used for limiting the
number of items read:

@table @asis
@item -1
Read all of the string or file until the end (default).

@item N
Read until the first of two conditions occurs: 1) the format has been
processed N times, or 2) N lines of the input have been processed.  Zero
(0) is an acceptable value for @var{repeat}.  Currently, end-of-line
characters inside %q, %c, and %[@dots{}]$ conversions do not contribute to
the line count.  This is incompatible with @sc{matlab} and may change in
future.
@end table

The behavior of @code{textscan} can be changed via property/value pairs.
The following properties are recognized:

@table @asis
@item @qcode{"BufSize"}
This specifies the number of bytes to use for the internal buffer.
A modest speed improvement may be obtained by setting this to a large value
when reading a large file, especially if the input contains long strings.
The default is 4096, or a value dependent on @var{n} if that is specified.

@item @qcode{"CollectOutput"}
A value of 1 or true instructs @code{textscan} to concatenate consecutive
columns of the same class in the output cell array.  A value of 0 or false
(default) leaves output in distinct columns.

@item @qcode{"CommentStyle"}
Specify parts of the input which are considered comments and will be
skipped.  @var{value} is the comment style and can be either (1) A string
or 1x1 cell string, to skip everything to the right of it; (2) A cell array
of two strings, to skip everything between the first and second strings.
Comments are only parsed where whitespace is accepted and do not act as
delimiters.

@item @qcode{"Delimiter"}
If @var{value} is a string, any character in @var{value} will be used to
split the input into words.  If @var{value} is a cell array of strings,
any string in the array will be used to split the input into words.
(default value = any whitespace.)

@item @qcode{"EmptyValue"}
Value to return for empty numeric values in non-whitespace delimited data.
The default is NaN@.  When the data type does not support NaN (int32 for
example), then the default is zero.

@item @qcode{"EndOfLine"}
@var{value} can be either an empty or one character specifying the
end-of-line character, or the pair
@qcode{"@backslashchar{}r@backslashchar{}n"} (CRLF).
In the latter case, any of
@qcode{"@backslashchar{}r"}, @qcode{"@backslashchar{}n"} or
@qcode{"@backslashchar{}r@backslashchar{}n"} is counted as a (single)
newline.  If no value is given,
@qcode{"@backslashchar{}r@backslashchar{}n"} is used.
@c If set to "" (empty string) EOLs are ignored as delimiters and added
@c to whitespace.

@c When reading from a character string, optional input argument @var{n}
@c specifies the number of times @var{format} should be used (i.e., to limit
@c the amount of data read).
@c When reading from file, @var{n} specifies the number of data lines to read;
@c in this sense it differs slightly from the format repeat count in strread.

@item @qcode{"HeaderLines"}
The first @var{value} number of lines of @var{fid} are skipped.  Note that
this does not refer to the first non-comment lines, but the first lines of
any type.

@item @qcode{"MultipleDelimsAsOne"}
If @var{value} is nonzero, treat a series of consecutive delimiters,
without whitespace in between, as a single delimiter.  Consecutive
delimiter series need not be vertically aligned.  Without this option, a
single delimiter before the end of the line does not cause the line to be
considered to end with an empty value, but a single delimiter at the start
of a line causes the line to be considered to start with an empty value.

@item @qcode{"TreatAsEmpty"}
Treat single occurrences (surrounded by delimiters or whitespace) of the
string(s) in @var{value} as missing values.

@item @qcode{"ReturnOnError"}
If set to numerical 1 or true, return normally as soon as an error is
encountered, such as trying to read a string using @code{%f}.
If set to 0 or false, return an error and no data.

@item @qcode{"Whitespace"}
Any character in @var{value} will be interpreted as whitespace and trimmed;
The default value for whitespace is
@c Note: the next line specifically has a newline which generates a space
@c       in the output of qcode, but keeps the next line < 80 characters.
@qcode{"
@backslashchar{}b@backslashchar{}r@backslashchar{}n@backslashchar{}t"}
(note the space).  Unless whitespace is set to @qcode{""} (empty) AND at
least one @qcode{"%s"} format conversion specifier is supplied, a space is
always part of whitespace.

@end table

When the number of words in @var{str} or @var{fid} doesn't match an exact
multiple of the number of format conversion specifiers, @code{textscan}'s
behavior depends on whether the last character of the string or file is an
end-of-line as specified by the @code{EndOfLine} option:

@table @asis
@item last character = end-of-line
Data columns are padded with empty fields, NaN or 0 (for integer fields) so
that all columns have equal length

@item last character is not end-of-line
Data columns are not padded; @code{textscan} returns columns of unequal
length
@end table

The second output @var{position} provides the location, in characters
from the beginning of the file or string, where processing stopped.

@xseealso{@ref{XREFdlmread,,dlmread}, @ref{XREFfscanf,,fscanf}, @ref{XREFload,,load}, @ref{XREFstrread,,strread}, @ref{XREFtextread,,textread}}
@end deftypefn


The @code{importdata} function has the ability to work with a wide
variety of data.

@c importdata scripts/io/importdata.m
@anchor{XREFimportdata}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{A} =} importdata (@var{fname})
@deftypefnx {} {@var{A} =} importdata (@var{fname}, @var{delimiter})
@deftypefnx {} {@var{A} =} importdata (@var{fname}, @var{delimiter}, @var{header_rows})
@deftypefnx {} {[@var{A}, @var{delimiter}] =} importdata (@dots{})
@deftypefnx {} {[@var{A}, @var{delimiter}, @var{header_rows}] =} importdata (@dots{})
Import data from the file @var{fname}.

Input parameters:

@itemize
@item @var{fname}
The name of the file containing data.

@item @var{delimiter}
The character separating columns of data.  Use @code{\t} for tab.
(Only valid for ASCII files)

@item @var{header_rows}
The number of header rows before the data begins.  (Only valid for ASCII
files)
@end itemize

Different file types are supported:

@itemize
@item ASCII table

Import ASCII table using the specified number of header rows and the
specified delimiter.

@item Image file

@item @sc{matlab} file

@item Spreadsheet files (depending on external software)

@item WAV file

@end itemize

@xseealso{@ref{XREFtextscan,,textscan}, @ref{XREFdlmread,,dlmread}, @ref{XREFcsvread,,csvread}, @ref{XREFload,,load}}
@end deftypefn


After importing, the data may need to be transformed before further analysis.
The @code{rescale} function can shift and normalize a data set to a specified
range.

@c rescale scripts/general/rescale.m
@anchor{XREFrescale}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{B} =} rescale (@var{A})
@deftypefnx {} {@var{B} =} rescale (@var{A}, @var{l}, @var{u})
@deftypefnx {} {@var{B} =} rescale (@dots{}, "inputmin", @var{inmin})
@deftypefnx {} {@var{B} =} rescale (@dots{}, "inputmax", @var{inmax})
Scale matrix elements to a specified range of values.

When called with a single matrix argument @var{A}, rescale elements to
occupy the interval [0, 1].

The optional inputs @code{[@var{l}, @var{u}]} will scale @var{A} to the
interval with lower bound @var{l} and upper bound @var{u}.

The optional input @qcode{"inputmin"} replaces all elements less than
the specified value @var{inmin} with @var{inmin}.  Similarly, the optional
input @qcode{"inputmax"} replaces all elements greater than the specified
value @var{inmax} with @var{inmax}.  If unspecified the minimum and maximum
are taken from the data itself (@w{@code{@var{inmin} = min (A(:))}}@ and
@w{@code{@var{inmax} = max (A(:))}}).

Programming Notes:
The applied formula is
@tex
$$B = l + {A - inmin \over inmax - inmin} \cdot (u - l)$$
@end tex
@ifnottex
@var{B} = @var{l} + ((@var{A} - @var{inmin}) ./ (@var{inmax} - @var{inmin}))
.* (@var{u} - @var{l})
@end ifnottex

The class of the output matrix @var{B} is single if the input @var{A} is
single, but otherwise is of class double for inputs which are of double,
integer, or logical type.

@xseealso{@ref{XREFbounds,,bounds}, @ref{XREFmin,,min}, @ref{XREFmax,,max}}
@end deftypefn


@menu
* Saving Data on Unexpected Exits::
@end menu

@node Saving Data on Unexpected Exits
@subsubsection Saving Data on Unexpected Exits

If Octave for some reason exits unexpectedly it will by default save the
variables available in the workspace to a file in the current directory.
By default this file is named @samp{octave-workspace} and can be loaded
into memory with the @code{load} command.  While the default behavior
most often is reasonable it can be changed through the following
functions.

@c crash_dumps_octave_core libinterp/corefcn/load-save.cc
@anchor{XREFcrash_dumps_octave_core}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} crash_dumps_octave_core ()
@deftypefnx {} {@var{old_val} =} crash_dumps_octave_core (@var{new_val})
@deftypefnx {} {@var{old_val} =} crash_dumps_octave_core (@var{new_val}, "local")
Query or set the internal variable that controls whether Octave tries
to save all current variables to the file @file{octave-workspace} if it
crashes or receives a hangup, terminate or similar signal.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFoctave_core_file_limit,,octave_core_file_limit}, @ref{XREFoctave_core_file_name,,octave_core_file_name}, @ref{XREFoctave_core_file_options,,octave_core_file_options}}
@end deftypefn


@c sighup_dumps_octave_core libinterp/corefcn/sighandlers.cc
@anchor{XREFsighup_dumps_octave_core}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} sighup_dumps_octave_core ()
@deftypefnx {} {@var{old_val} =} sighup_dumps_octave_core (@var{new_val})
@deftypefnx {} {@var{old_val} =} sighup_dumps_octave_core (@var{new_val}, "local")
Query or set the internal variable that controls whether Octave tries
to save all current variables to the file @file{octave-workspace} if it
receives a hangup signal.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@end deftypefn


@c sigquit_dumps_octave_core libinterp/corefcn/sighandlers.cc
@anchor{XREFsigquit_dumps_octave_core}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} sigquit_dumps_octave_core ()
@deftypefnx {} {@var{old_val} =} sigquit_dumps_octave_core (@var{new_val})
@deftypefnx {} {@var{old_val} =} sigquit_dumps_octave_core (@var{new_val}, "local")
Query or set the internal variable that controls whether Octave tries
to save all current variables to the file @file{octave-workspace} if it
receives a quit signal.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@end deftypefn


@c sigterm_dumps_octave_core libinterp/corefcn/sighandlers.cc
@anchor{XREFsigterm_dumps_octave_core}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} sigterm_dumps_octave_core ()
@deftypefnx {} {@var{old_val} =} sigterm_dumps_octave_core (@var{new_val})
@deftypefnx {} {@var{old_val} =} sigterm_dumps_octave_core (@var{new_val}, "local")
Query or set the internal variable that controls whether Octave tries
to save all current variables to the file @file{octave-workspace} if it
receives a terminate signal.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@end deftypefn


@c octave_core_file_options libinterp/corefcn/load-save.cc
@anchor{XREFoctave_core_file_options}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} octave_core_file_options ()
@deftypefnx {} {@var{old_val} =} octave_core_file_options (@var{new_val})
@deftypefnx {} {@var{old_val} =} octave_core_file_options (@var{new_val}, "local")
Query or set the internal variable that specifies the options used for
saving the workspace data if Octave aborts.

The value of @code{octave_core_file_options} should follow the same format
as the options for the @code{save} function.  The default value is Octave's
binary format.

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFcrash_dumps_octave_core,,crash_dumps_octave_core}, @ref{XREFoctave_core_file_name,,octave_core_file_name}, @ref{XREFoctave_core_file_limit,,octave_core_file_limit}}
@end deftypefn


@c octave_core_file_limit libinterp/corefcn/load-save.cc
@anchor{XREFoctave_core_file_limit}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} octave_core_file_limit ()
@deftypefnx {} {@var{old_val} =} octave_core_file_limit (@var{new_val})
@deftypefnx {} {@var{old_val} =} octave_core_file_limit (@var{new_val}, "local")
Query or set the internal variable that specifies the maximum amount of memory
that Octave will save when writing a crash dump file.

The limit is measured in kilobytes and is applied to the top-level workspace.
The name of the crash dump file is specified by
@var{octave_core_file_name}.

If @var{octave_core_file_options} flags specify a binary format, then
@var{octave_core_file_limit} will be approximately the maximum size of the
file.  If a text file format is used, then the file could be much larger than
the limit.  The default value is -1 (unlimited).

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFcrash_dumps_octave_core,,crash_dumps_octave_core}, @ref{XREFoctave_core_file_name,,octave_core_file_name}, @ref{XREFoctave_core_file_options,,octave_core_file_options}}
@end deftypefn


@c octave_core_file_name libinterp/corefcn/load-save.cc
@anchor{XREFoctave_core_file_name}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} octave_core_file_name ()
@deftypefnx {} {@var{old_val} =} octave_core_file_name (@var{new_val})
@deftypefnx {} {@var{old_val} =} octave_core_file_name (@var{new_val}, "local")
Query or set the internal variable that specifies the name of the file
used for saving data from the top-level workspace if Octave aborts.

The default value is @qcode{"octave-workspace"}

When called from inside a function with the @qcode{"local"} option, the
variable is changed locally for the function and any subroutines it calls.
The original variable value is restored when exiting the function.
@xseealso{@ref{XREFcrash_dumps_octave_core,,crash_dumps_octave_core}, @ref{XREFoctave_core_file_name,,octave_core_file_name}, @ref{XREFoctave_core_file_options,,octave_core_file_options}}
@end deftypefn


@node C-Style I/O Functions
@section C-Style I/O Functions

Octave's C-style input and output functions provide most of the
functionality of the C programming language's standard I/O library.  The
argument lists for some of the input functions are slightly different,
however, because Octave has no way of passing arguments by reference.

In the following, @var{file} refers to a filename and @code{fid} refers
to an integer file number, as returned by @code{fopen}.

There are three files that are always available.  Although these files
can be accessed using their corresponding numeric file ids, you should
always use the symbolic names given in the table below, since it will
make your programs easier to understand.

@c stdin libinterp/corefcn/file-io.cc
@anchor{XREFstdin}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{fid} =} stdin ()
Return the numeric value corresponding to the standard input stream.

When Octave is used interactively, stdin is filtered through the command
line editing functions.
@xseealso{@ref{XREFstdout,,stdout}, @ref{XREFstderr,,stderr}}
@end deftypefn


@c stdout libinterp/corefcn/file-io.cc
@anchor{XREFstdout}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{fid} =} stdout ()
Return the numeric value corresponding to the standard output stream.

Data written to the standard output may be filtered through the pager.
@xseealso{@ref{XREFstdin,,stdin}, @ref{XREFstderr,,stderr}, @ref{XREFpage_screen_output,,page_screen_output}}
@end deftypefn


@c stderr libinterp/corefcn/file-io.cc
@anchor{XREFstderr}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{fid} =} stderr ()
Return the numeric value corresponding to the standard error stream.

Even if paging is turned on, the standard error is not sent to the pager.
It is useful for error messages and prompts.
@xseealso{@ref{XREFstdin,,stdin}, @ref{XREFstdout,,stdout}}
@end deftypefn


@menu
* Opening and Closing Files::
* Simple Output::
* Line-Oriented Input::
* Formatted Output::
* Output Conversion for Matrices::
* Output Conversion Syntax::
* Table of Output Conversions::
* Integer Conversions::
* Floating-Point Conversions::
* Other Output Conversions::
* Formatted Input::
* Input Conversion Syntax::
* Table of Input Conversions::
* Numeric Input Conversions::
* String Input Conversions::
* Binary I/O::
* Temporary Files::
* EOF (End of File) and Errors::
* File Positioning::
@end menu

@node Opening and Closing Files
@subsection Opening and Closing Files

When reading data from a file it must be opened for reading first, and
likewise when writing to a file.  The @code{fopen} function returns a
pointer to an open file that is ready to be read or written.  Once all
data has been read from or written to the opened file it should be closed.
The @code{fclose} function does this.  The following code illustrates
the basic pattern for writing to a file, but a very similar pattern is
used when reading a file.

@example
@group
filename = "myfile.txt";
fid = fopen (filename, "w");
# Do the actual I/O here@dots{}
fclose (fid);
@end group
@end example

@c fopen libinterp/corefcn/file-io.cc
@anchor{XREFfopen}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{fid} =} fopen (@var{name})
@deftypefnx {} {@var{fid} =} fopen (@var{name}, @var{mode})
@deftypefnx {} {@var{fid} =} fopen (@var{name}, @var{mode}, @var{arch})
@deftypefnx {} {@var{fid} =} fopen (@var{name}, @var{mode}, @var{arch}, @var{encoding})
@deftypefnx {} {[@var{fid}, @var{msg}] =} fopen (@dots{})
@deftypefnx {} {@var{fid_list} =} fopen ("all")
@deftypefnx {} {[@var{file}, @var{mode}, @var{arch}, @var{encoding}] =} fopen (@var{fid})
Open a file for low-level I/O or query open files and file descriptors.

The first form of the @code{fopen} function opens the named file with
the specified mode (read-write, read-only, etc.@:), architecture
interpretation (IEEE big endian, IEEE little endian, etc.@:) and file encoding,
and returns an integer value that may be used to refer to the file later.  If
an error occurs, @var{fid} is set to @minus{}1 and @var{msg} contains the
corresponding system error message.  The @var{mode} is a one or two
character string that specifies whether the file is to be opened for
reading, writing, or both.  The @var{encoding} is a character string with a
valid encoding identifier.  This encoding is used when strings are read from
or written to the file.  By default, that is UTF-8.

The second form of the @code{fopen} function returns a vector of file ids
corresponding to all the currently open files, excluding the
@code{stdin}, @code{stdout}, and @code{stderr} streams.

The third form of the @code{fopen} function returns information about the
open file given its file id.

For example,

@example
myfile = fopen ("splat.dat", "r", "ieee-le");
@end example

@noindent
opens the file @file{splat.dat} for reading.  If necessary, binary
numeric values will be read assuming they are stored in IEEE@tie{}754 format
with the least significant bit first, and then converted to the native
representation.

Opening a file that is already open simply opens it again and returns a
separate file id.  It is not an error to open a file several times,
though writing to the same file through several different file ids may
produce unexpected results.

The possible values of @var{mode} are

@table @asis
@item @samp{r} (default)
Open a file for reading.

@item @samp{w}
Open a file for writing.  The previous contents are discarded.

@item @samp{a}
Open or create a file for writing at the end of the file.

@item @samp{r+}
Open an existing file for reading and writing.

@item @samp{w+}
Open a file for reading or writing.  The previous contents are
discarded.

@item @samp{a+}
Open or create a file for reading or writing at the end of the
file.
@end table

Append a @qcode{"t"} to the mode string to open the file in text mode or a
@qcode{"b"} to open in binary mode.  On Windows systems,
text mode reading and writing automatically converts linefeeds to the
appropriate line end character for the system (carriage-return linefeed on
Windows).  The default when no mode is specified is binary.

Additionally, you may append a @qcode{"z"} to the mode string to open a
gzipped file for reading or writing.  For this to be successful, you
must also open the file in binary mode.

The parameter @var{arch} is a string specifying the default data format
for the file.  Valid values for @var{arch} are:

@table @asis
@item @qcode{"native"} or @qcode{"n"} (default)
The format of the current machine.

@item @qcode{"ieee-be"} or @qcode{"b"}
IEEE big endian format.

@item @qcode{"ieee-le"} or @qcode{"l"}
IEEE little endian format.
@end table

When opening a new file that does not yet exist, permissions will be set to
@code{0666 - @var{umask}}.

Compatibility Note: Octave opens files using buffered I/O.  Small writes are
accumulated until an internal buffer is filled, and then everything is written
in a single operation.  This is very efficient and improves performance.
@sc{matlab}, however, opens files using flushed I/O where every write operation
is immediately performed.  If the write operation must be performed immediately
after data has been written then the write should be followed by a call to
@code{fflush} to flush the internal buffer.
@xseealso{@ref{XREFfclose,,fclose}, @ref{XREFfgets,,fgets}, @ref{XREFfgetl,,fgetl}, @ref{XREFfscanf,,fscanf}, @ref{XREFfread,,fread}, @ref{XREFfputs,,fputs}, @ref{XREFfdisp,,fdisp}, @ref{XREFfprintf,,fprintf}, @ref{XREFfwrite,,fwrite}, @ref{XREFfskipl,,fskipl}, @ref{XREFfseek,,fseek}, @ref{XREFfrewind,,frewind}, @ref{XREFftell,,ftell}, @ref{XREFfeof,,feof}, @ref{XREFferror,,ferror}, @ref{XREFfclear,,fclear}, @ref{XREFfflush,,fflush}, @ref{XREFfreport,,freport}, @ref{XREFumask,,umask}}
@end deftypefn


@c fclose libinterp/corefcn/file-io.cc
@anchor{XREFfclose}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{status} =} fclose (@var{fid})
@deftypefnx {} {@var{status} =} fclose ("all")
Close the file specified by the file descriptor @var{fid}.

If successful, @code{fclose} returns 0, otherwise, it returns -1.  The
second form of the @code{fclose} call closes all open files except
@code{stdin}, @code{stdout}, @code{stderr}, and any FIDs associated
with gnuplot.
@xseealso{@ref{XREFfopen,,fopen}, @ref{XREFfflush,,fflush}, @ref{XREFfreport,,freport}}
@end deftypefn


@c is_valid_file_id scripts/io/is_valid_file_id.m
@anchor{XREFis_valid_file_id}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{tf} =} is_valid_file_id (@var{fid})
Return true if @var{fid} refers to an open file.
@xseealso{@ref{XREFfreport,,freport}, @ref{XREFfopen,,fopen}}
@end deftypefn


@node Simple Output
@subsection Simple Output

Once a file has been opened for writing a string can be written to the
file using the @code{fputs} function.  The following example shows
how to write the string @samp{Free Software is needed for Free Science}
to the file @samp{free.txt}.

@example
@group
filename = "free.txt";
fid = fopen (filename, "w");
fputs (fid, "Free Software is needed for Free Science");
fclose (fid);
@end group
@end example

@c fputs libinterp/corefcn/file-io.cc
@anchor{XREFfputs}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{status} =} fputs (@var{fid}, @var{string})
Write the string @var{string} to the file with file descriptor @var{fid}.

The string is written to the file with no additional formatting.  Use
@code{fdisp} instead to automatically append a newline character appropriate
for the local machine.

The optional output @var{status} is 0 for success, or -1 if an error was
encountered.
@xseealso{@ref{XREFfdisp,,fdisp}, @ref{XREFfprintf,,fprintf}, @ref{XREFfwrite,,fwrite}, @ref{XREFfopen,,fopen}}
@end deftypefn


A function much similar to @code{fputs} is available for writing data
to the screen.  The @code{puts} function works just like @code{fputs}
except it doesn't take a file pointer as its input.

@c puts libinterp/corefcn/file-io.cc
@anchor{XREFputs}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{status} =} puts (@var{string})
Write a string to the standard output with no formatting.

The string is written verbatim to the standard output.  Use @code{disp} to
automatically append a newline character appropriate for the local machine.

The optional output @var{status} is 0 for success, or -1 if an error was
encountered.
@xseealso{@ref{XREFfputs,,fputs}, @ref{XREFdisp,,disp}}
@end deftypefn


@node Line-Oriented Input
@subsection Line-Oriented Input

To read from a file it must be opened for reading using @code{fopen}.
Then a line can be read from the file using @code{fgetl} as the following
code illustrates

@example
@group
fid = fopen ("free.txt");
txt = fgetl (fid)
     @print{} Free Software is needed for Free Science
fclose (fid);
@end group
@end example

@noindent
This of course assumes that the file @samp{free.txt} exists and contains
the line @samp{Free Software is needed for Free Science}.

@c fgetl libinterp/corefcn/file-io.cc
@anchor{XREFfgetl}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{str} =} fgetl (@var{fid})
@deftypefnx {} {@var{str} =} fgetl (@var{fid}, @var{len})
Read characters from a file, stopping after a newline, or EOF,
or @var{len} characters have been read.

The characters read, excluding the possible trailing newline, are returned
as a string.

If @var{len} is omitted, @code{fgetl} reads until the next newline
character.

If there are no more characters to read, @code{fgetl} returns @minus{}1.

To read a line and return the terminating newline,
@pxref{XREFfgets,,@code{fgets}}.
@xseealso{@ref{XREFfgets,,fgets}, @ref{XREFfscanf,,fscanf}, @ref{XREFfread,,fread}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c fgets libinterp/corefcn/file-io.cc
@anchor{XREFfgets}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{str} =} fgets (@var{fid})
@deftypefnx {} {@var{str} =} fgets (@var{fid}, @var{len})
Read characters from a file, stopping after a newline, or EOF,
or @var{len} characters have been read.

The characters read, including the possible trailing newline, are returned
as a string.

If @var{len} is omitted, @code{fgets} reads until the next newline
character.

If there are no more characters to read, @code{fgets} returns @minus{}1.

To read a line and discard the terminating newline,
@pxref{XREFfgetl,,@code{fgetl}}.
@xseealso{@ref{XREFfputs,,fputs}, @ref{XREFfgetl,,fgetl}, @ref{XREFfscanf,,fscanf}, @ref{XREFfread,,fread}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c fskipl libinterp/corefcn/file-io.cc
@anchor{XREFfskipl}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{nlines} =} fskipl (@var{fid})
@deftypefnx {} {@var{nlines} =} fskipl (@var{fid}, @var{count})
@deftypefnx {} {@var{nlines} =} fskipl (@var{fid}, Inf)
Read and skip @var{count} lines from the file specified by the file
descriptor @var{fid}.

@code{fskipl} discards characters until an end-of-line is encountered
exactly @var{count}-times, or until the end-of-file marker is found.

If @var{count} is omitted, it defaults to 1.  @var{count} may also be
@code{Inf}, in which case lines are skipped until the end of the file.
This form is suitable for counting the number of lines in a file.

Returns the number of lines skipped (end-of-line sequences encountered).
@xseealso{@ref{XREFfgetl,,fgetl}, @ref{XREFfgets,,fgets}, @ref{XREFfscanf,,fscanf}, @ref{XREFfopen,,fopen}}
@end deftypefn


@node Formatted Output
@subsection Formatted Output

This section describes how to call @code{printf} and related functions.

The following functions are available for formatted output.  They are
modeled after the C language functions of the same name, but they
interpret the format template differently in order to improve the
performance of printing vector and matrix values.

Implementation Note: For compatibility with @sc{matlab}, escape sequences in
the template string (e.g., @qcode{"@backslashchar{}n"} => newline) are
expanded even when the template string is defined with single quotes.

@c printf libinterp/corefcn/file-io.cc
@anchor{XREFprintf}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} printf (@var{template}, @dots{})
@deftypefnx {} {@var{numbytes} =} printf (@dots{})
Print optional arguments under the control of the template string
@var{template} to the stream @code{stdout} and return the number of characters
printed.
@ifclear OCTAVE_MANUAL

See the Formatted Output section of the GNU Octave manual for a complete
description of the syntax of the template string.
@end ifclear

The optional output @var{numbytes} returns the number of bytes printed.

Implementation Note: For compatibility with @sc{matlab}, escape sequences in
the template string (e.g., @qcode{"@backslashchar{}n"} => newline) are
expanded even when the template string is defined with single quotes.
@xseealso{@ref{XREFfprintf,,fprintf}, @ref{XREFsprintf,,sprintf}, @ref{XREFscanf,,scanf}}
@end deftypefn


@c fprintf libinterp/corefcn/file-io.cc
@anchor{XREFfprintf}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} fprintf (@var{fid}, @var{template}, @dots{})
@deftypefnx {} {} fprintf (@var{template}, @dots{})
@deftypefnx {} {@var{numbytes} =} fprintf (@dots{})
This function is equivalent to @code{printf}, except that the output is
written to the file descriptor @var{fid} instead of @code{stdout}.

If @var{fid} is omitted, the output is written to @code{stdout} making the
function exactly equivalent to @code{printf}.

The optional output @var{numbytes} returns the number of bytes written to the
file.

Implementation Note: For compatibility with @sc{matlab}, escape sequences in
the template string (e.g., @qcode{"@backslashchar{}n"} => newline) are
expanded even when the template string is defined with single quotes.
@xseealso{@ref{XREFfputs,,fputs}, @ref{XREFfdisp,,fdisp}, @ref{XREFfwrite,,fwrite}, @ref{XREFfscanf,,fscanf}, @ref{XREFprintf,,printf}, @ref{XREFsprintf,,sprintf}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c sprintf libinterp/corefcn/file-io.cc
@anchor{XREFsprintf}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{str} =} sprintf (@var{template}, @dots{})
This is like @code{printf}, except that the output is returned as a
string.

Unlike the C library function, which requires you to provide a suitably
sized string as an argument, Octave's @code{sprintf} function returns the
string, automatically sized to hold all of the items converted.

Implementation Note: For compatibility with @sc{matlab}, escape sequences in
the template string (e.g., @qcode{"@backslashchar{}n"} => newline) are
expanded even when the template string is defined with single quotes.
@xseealso{@ref{XREFprintf,,printf}, @ref{XREFfprintf,,fprintf}, @ref{XREFsscanf,,sscanf}}
@end deftypefn


The @code{printf} function can be used to print any number of arguments.
The template string argument you supply in a call provides
information not only about the number of additional arguments, but also
about their types and what style should be used for printing them.

Ordinary characters in the template string are simply written to the
output stream as-is, while @dfn{conversion specifications} introduced by
a @samp{%} character in the template cause subsequent arguments to be
formatted and written to the output stream.  For example,
@cindex conversion specifications (@code{printf})

@example
@group
pct = 37;
filename = "foo.txt";
printf ("Processed %d%% of '%s'.\nPlease be patient.\n",
        pct, filename);
@end group
@end example

@noindent
produces output like

@example
@group
Processed 37% of 'foo.txt'.
Please be patient.
@end group
@end example

This example shows the use of the @samp{%d} conversion to specify that a
scalar argument should be printed in decimal notation, the @samp{%s}
conversion to specify printing of a string argument, and the @samp{%%}
conversion to print a literal @samp{%} character.

There are also conversions for printing an integer argument as an
unsigned value in octal, decimal, or hexadecimal radix (@samp{%o},
@samp{%u}, or @samp{%x}, respectively); or as a character value
(@samp{%c}).

Floating-point numbers can be printed in normal, fixed-point notation
using the @samp{%f} conversion or in exponential notation using the
@samp{%e} conversion.  The @samp{%g} conversion uses either @samp{%e}
or @samp{%f} format, depending on what is more appropriate for the
magnitude of the particular number.

You can control formatting more precisely by writing @dfn{modifiers}
between the @samp{%} and the character that indicates which conversion
to apply.  These slightly alter the ordinary behavior of the conversion.
For example, most conversion specifications permit you to specify a
minimum field width and a flag indicating whether you want the result
left- or right-justified within the field.

The specific flags and modifiers that are permitted and their
interpretation vary depending on the particular conversion.  They're all
described in more detail in the following sections.

@node Output Conversion for Matrices
@subsection Output Conversion for Matrices

When given a matrix value, Octave's formatted output functions cycle
through the format template until all the values in the matrix have been
printed.  For example:

@example
@group
printf ("%4.2f %10.2e %8.4g\n", hilb (3));

     @print{} 1.00   5.00e-01   0.3333
     @print{} 0.50   3.33e-01     0.25
     @print{} 0.33   2.50e-01      0.2
@end group
@end example

If more than one value is to be printed in a single call, the output
functions do not return to the beginning of the format template when
moving on from one value to the next.  This can lead to confusing output
if the number of elements in the matrices are not exact multiples of the
number of conversions in the format template.  For example:

@example
@group
printf ("%4.2f %10.2e %8.4g\n", [1, 2], [3, 4]);

     @print{} 1.00   2.00e+00        3
     @print{} 4.00
@end group
@end example

If this is not what you want, use a series of calls instead of just one.

@node Output Conversion Syntax
@subsection Output Conversion Syntax

This section provides details about the precise syntax of conversion
specifications that can appear in a @code{printf} template
string.

Characters in the template string that are not part of a
conversion specification are printed as-is to the output stream.

The conversion specifications in a @code{printf} template string have
the general form:

@example
% @var{flags} @var{width} @r{[} . @var{precision} @r{]} @var{type} @var{conversion}
@end example

For example, in the conversion specifier @samp{%-10.8ld}, the @samp{-}
is a flag, @samp{10} specifies the field width, the precision is
@samp{8}, the letter @samp{l} is a type modifier, and @samp{d} specifies
the conversion style.  (This particular type specifier says to print a
numeric argument in decimal notation, with a minimum of 8 digits
left-justified in a field at least 10 characters wide.)

In more detail, output conversion specifications consist of an
initial @samp{%} character followed in sequence by:

@itemize @bullet
@item
Zero or more @dfn{flag characters} that modify the normal behavior of
the conversion specification.
@cindex flag character (@code{printf})

@item
An optional decimal integer specifying the @dfn{minimum field width}.
If the normal conversion produces fewer characters than this, the field
is padded with spaces to the specified width.  This is a @emph{minimum}
value; if the normal conversion produces more characters than this, the
field is @emph{not} truncated.  Normally, the output is right-justified
within the field.
@cindex minimum field width (@code{printf})

You can also specify a field width of @samp{*}.  This means that the
next argument in the argument list (before the actual value to be
printed) is used as the field width.  The value is rounded to the
nearest integer.  If the value is negative, this means to set the
@samp{-} flag (see below) and to use the absolute value as the field
width.

@item
An optional @dfn{precision} to specify the number of digits to be
written for the numeric conversions.  If the precision is specified, it
consists of a period (@samp{.}) followed optionally by a decimal integer
(which defaults to zero if omitted).
@cindex precision (@code{printf})

You can also specify a precision of @samp{*}.  This means that the next
argument in the argument list (before the actual value to be printed) is
used as the precision.  The value must be an integer, and is ignored
if it is negative.

@item
An optional @dfn{type modifier character}.  This character is ignored by
Octave's @code{printf} function, but is recognized to provide
compatibility with the C language @code{printf}.

@item
A character that specifies the conversion to be applied.
@end itemize

The exact options that are permitted and how they are interpreted vary
between the different conversion specifiers.  See the descriptions of the
individual conversions for information about the particular options that
they use.

@node Table of Output Conversions
@subsection Table of Output Conversions
@cindex output conversions, for @code{printf}

Here is a table summarizing what all the different conversions do:

@table @asis
@item @samp{%d}, @samp{%i}
Print an integer as a signed decimal number.  @xref{Integer Conversions}, for
details.  @samp{%d} and @samp{%i} are synonymous for
output, but are different when used with @code{scanf} for input
(@pxref{Table of Input Conversions}).

@item @samp{%o}
Print an integer as an unsigned octal number.  @xref{Integer Conversions}, for
details.

@item @samp{%u}
Print an integer as an unsigned decimal number.  @xref{Integer Conversions},
for details.

@item @samp{%x}, @samp{%X}
Print an integer as an unsigned hexadecimal number.  @samp{%x} uses
lowercase letters and @samp{%X} uses uppercase.  @xref{Integer Conversions},
for details.

@item @samp{%f}
Print a floating-point number in normal (fixed-point) notation.
@xref{Floating-Point Conversions}, for details.

@item @samp{%e}, @samp{%E}
Print a floating-point number in exponential notation.  @samp{%e} uses
lowercase letters and @samp{%E} uses uppercase.
@xref{Floating-Point Conversions}, for details.

@item @samp{%g}, @samp{%G}
Print a floating-point number in either normal (fixed-point) or
exponential notation, whichever is more appropriate for its magnitude.
@samp{%g} uses lowercase letters and @samp{%G} uses uppercase.
@xref{Floating-Point Conversions}, for details.

@item @samp{%c}
Print a single character.  @xref{Other Output Conversions}.

@item @samp{%s}
Print a string.  @xref{Other Output Conversions}.

@item @samp{%%}
Print a literal @samp{%} character.  @xref{Other Output Conversions}.
@end table

If the syntax of a conversion specification is invalid, unpredictable
things will happen, so don't do this.  In particular, @sc{matlab} allows
a bare percentage sign @samp{%} with no subsequent conversion character.
Octave will emit an error and stop if it sees such code.  When the string
variable to be processed cannot be guaranteed to be free of potential format
codes it is better to use the two argument form of any of the @code{printf}
functions and set the format string to @code{%s}.  Alternatively, for code
which is not required to be backwards-compatible with @sc{matlab} the
Octave function @code{puts} or @code{disp} can be used.

@example
@group
printf (strvar);        # Unsafe if strvar contains format codes
printf ("%s", strvar);  # Safe
puts (strvar);          # Safe
@end group
@end example

If there aren't enough function arguments provided to supply values for all
the conversion specifications in the template string, or if the arguments are
not of the correct types, the results are unpredictable.  If you supply more
arguments than conversion specifications, the extra argument values are
simply ignored; this is sometimes useful.

@node Integer Conversions
@subsection Integer Conversions

This section describes the options for the @samp{%d}, @samp{%i},
@samp{%o}, @samp{%u}, @samp{%x}, and @samp{%X} conversion
specifications.  These conversions print integers in various formats.

The @samp{%d} and @samp{%i} conversion specifications both print an
numeric argument as a signed decimal number; while @samp{%o},
@samp{%u}, and @samp{%x} print the argument as an unsigned octal,
decimal, or hexadecimal number (respectively).  The @samp{%X} conversion
specification is just like @samp{%x} except that it uses the characters
@samp{ABCDEF} as digits instead of @samp{abcdef}.

The following flags are meaningful:

@table @asis
@item @samp{-}
Left-justify the result in the field (instead of the normal
right-justification).

@item @samp{+}
For the signed @samp{%d} and @samp{%i} conversions, print a
plus sign if the value is positive.

@item @samp{ }
For the signed @samp{%d} and @samp{%i} conversions, if the result
doesn't start with a plus or minus sign, prefix it with a space
character instead.  Since the @samp{+} flag ensures that the result
includes a sign, this flag is ignored if you supply both of them.

@item @samp{#}
For the @samp{%o} conversion, this forces the leading digit to be
@samp{0}, as if by increasing the precision.  For @samp{%x} or
@samp{%X}, this prefixes a leading @samp{0x} or @samp{0X} (respectively)
to the result.  This doesn't do anything useful for the @samp{%d},
@samp{%i}, or @samp{%u} conversions.

@item @samp{0}
Pad the field with zeros instead of spaces.  The zeros are placed after
any indication of sign or base.  This flag is ignored if the @samp{-}
flag is also specified, or if a precision is specified.
@end table

If a precision is supplied, it specifies the minimum number of digits to
appear; leading zeros are produced if necessary.  If you don't specify a
precision, the number is printed with as many digits as it needs.  If
you convert a value of zero with an explicit precision of zero, then no
characters at all are produced.

@node Floating-Point Conversions
@subsection Floating-Point Conversions

This section discusses the conversion specifications for floating-point
numbers: the @samp{%f}, @samp{%e}, @samp{%E}, @samp{%g}, and @samp{%G}
conversions.

The @samp{%f} conversion prints its argument in fixed-point notation,
producing output of the form
@w{[@code{-}]@var{ddd}@code{.}@var{ddd}},
where the number of digits following the decimal point is controlled
by the precision you specify.

The @samp{%e} conversion prints its argument in exponential notation,
producing output of the form
@w{[@code{-}]@var{d}@code{.}@var{ddd}@code{e}[@code{+}|@code{-}]@var{dd}}.
Again, the number of digits following the decimal point is controlled by
the precision.  The exponent always contains at least two digits.  The
@samp{%E} conversion is similar but the exponent is marked with the letter
@samp{E} instead of @samp{e}.

The @samp{%g} and @samp{%G} conversions print the argument in the style
of @samp{%e} or @samp{%E} (respectively) if the exponent would be less
than -4 or greater than or equal to the precision; otherwise they use the
@samp{%f} style.  Trailing zeros are removed from the fractional portion
of the result and a decimal-point character appears only if it is
followed by a digit.

The following flags can be used to modify the behavior:
@c Not @samp so we can have ' ' as an item.

@table @asis
@item @samp{-}
Left-justify the result in the field.  Normally the result is
right-justified.

@item @samp{+}
Always include a plus or minus sign in the result.

@item @samp{ }
If the result doesn't start with a plus or minus sign, prefix it with a
space instead.  Since the @samp{+} flag ensures that the result includes
a sign, this flag is ignored if you supply both of them.

@item @samp{#}
Specifies that the result should always include a decimal point, even
if no digits follow it.  For the @samp{%g} and @samp{%G} conversions,
this also forces trailing zeros after the decimal point to be left
in place where they would otherwise be removed.

@item @samp{0}
Pad the field with zeros instead of spaces; the zeros are placed
after any sign.  This flag is ignored if the @samp{-} flag is also
specified.
@end table

The precision specifies how many digits follow the decimal-point
character for the @samp{%f}, @samp{%e}, and @samp{%E} conversions.  For
these conversions, the default precision is @code{6}.  If the precision
is explicitly @code{0}, this suppresses the decimal point character
entirely.  For the @samp{%g} and @samp{%G} conversions, the precision
specifies how many significant digits to print.  Significant digits are
the first digit before the decimal point, and all the digits after it.
If the precision is @code{0} or not specified for @samp{%g} or
@samp{%G}, it is treated like a value of @code{1}.  If the value being
printed cannot be expressed precisely in the specified number of digits,
the value is rounded to the nearest number that fits.

@node Other Output Conversions
@subsection Other Output Conversions

This section describes miscellaneous conversions for @code{printf}.

The @samp{%c} conversion prints a single character.  The @samp{-}
flag can be used to specify left-justification in the field, but no
other flags are defined, and no precision or type modifier can be given.
For example:

@example
printf ("%c%c%c%c%c", "h", "e", "l", "l", "o");
@end example

@noindent
prints @samp{hello}.

The @samp{%s} conversion prints a string.  The corresponding argument
must be a string.  A precision can be specified to indicate the maximum
number of characters to write; otherwise characters in the string up to
but not including the terminating null character are written to the
output stream.  The @samp{-} flag can be used to specify
left-justification in the field, but no other flags or type modifiers
are defined for this conversion.  For example:

@example
printf ("%3s%-6s", "no", "where");
@end example

@noindent
prints @samp{ nowhere } (note the leading and trailing spaces).

@node Formatted Input
@subsection Formatted Input

Octave provides the @code{scanf}, @code{fscanf}, and @code{sscanf}
functions to read formatted input.  There are two forms of each of these
functions.  One can be used to extract vectors of data from a file, and
the other is more `C-like'.

@c fscanf libinterp/corefcn/file-io.cc
@anchor{XREFfscanf}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {[@var{val}, @var{count}, @var{errmsg}] =} fscanf (@var{fid}, @var{template}, @var{size})
@deftypefnx {} {[@var{v1}, @var{v2}, @dots{}, @var{count}, @var{errmsg}] =} fscanf (@var{fid}, @var{template}, "C")
In the first form, read from @var{fid} according to @var{template},
returning the result in the matrix @var{val}.

The optional argument @var{size} specifies the amount of data to read
and may be one of

@table @code
@item Inf
Read as much as possible, returning a column vector.

@item @var{nr}
Read up to @var{nr} elements, returning a column vector.

@item [@var{nr}, Inf]
Read as much as possible, returning a matrix with @var{nr} rows.  If the
number of elements read is not an exact multiple of @var{nr}, the last
column is padded with zeros.

@item [@var{nr}, @var{nc}]
Read up to @code{@var{nr} * @var{nc}} elements, returning a matrix with
@var{nr} rows.  If the number of elements read is not an exact multiple
of @var{nr}, the last column is padded with zeros.
@end table

@noindent
If @var{size} is omitted, a value of @code{Inf} is assumed.

A string is returned if @var{template} specifies only character conversions.

The number of items successfully read is returned in @var{count}.

If an error occurs, @var{errmsg} contains a system-dependent error message.

In the second form, read from @var{fid} according to @var{template},
with each conversion specifier in @var{template} corresponding to a
single scalar return value.  This form is more ``C-like'', and also
compatible with previous versions of Octave.  The number of successful
conversions is returned in @var{count}
@ifclear OCTAVE_MANUAL

See the Formatted Input section of the GNU Octave manual for a
complete description of the syntax of the template string.
@end ifclear
@xseealso{@ref{XREFfgets,,fgets}, @ref{XREFfgetl,,fgetl}, @ref{XREFfread,,fread}, @ref{XREFscanf,,scanf}, @ref{XREFsscanf,,sscanf}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c scanf libinterp/corefcn/file-io.cc
@anchor{XREFscanf}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {[@var{val}, @var{count}, @var{errmsg}] =} scanf (@var{template}, @var{size})
@deftypefnx {} {[@var{v1}, @var{v2}, @dots{}, @var{count}, @var{errmsg}] =} scanf (@var{template}, "C")
This is equivalent to calling @code{fscanf} with @var{fid} = @code{stdin}.

It is currently not useful to call @code{scanf} in interactive programs.
@xseealso{@ref{XREFfscanf,,fscanf}, @ref{XREFsscanf,,sscanf}, @ref{XREFprintf,,printf}}
@end deftypefn


@c sscanf libinterp/corefcn/file-io.cc
@anchor{XREFsscanf}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {[@var{val}, @var{count}, @var{errmsg}, @var{pos}] =} sscanf (@var{string}, @var{template}, @var{size})
@deftypefnx {} {[@var{v1}, @var{v2}, @dots{}, @var{count}, @var{errmsg}] =} sscanf (@var{string}, @var{template}, "C")
This is like @code{fscanf}, except that the characters are taken from the
string @var{string} instead of from a stream.

Reaching the end of the string is treated as an end-of-file condition.  In
addition to the values returned by @code{fscanf}, the index of the next
character to be read is returned in @var{pos}.
@xseealso{@ref{XREFfscanf,,fscanf}, @ref{XREFscanf,,scanf}, @ref{XREFsprintf,,sprintf}}
@end deftypefn


Calls to @code{scanf} are superficially similar to calls to
@code{printf} in that arbitrary arguments are read under the control of
a template string.  While the syntax of the conversion specifications in
the template is very similar to that for @code{printf}, the
interpretation of the template is oriented more towards free-format
input and simple pattern matching, rather than fixed-field formatting.
For example, most @code{scanf} conversions skip over any amount of
``white space'' (including spaces, tabs, and newlines) in the input
file, and there is no concept of precision for the numeric input
conversions as there is for the corresponding output conversions.
Ordinarily, non-whitespace characters in the template are expected to
match characters in the input stream exactly.  For example, note that
@code{sscanf} parses the string and whitespace differently when using
mixed numeric and string output types:
@cindex conversion specifications (@code{scanf})

@example
@group
teststr = "1 is a lonely number";
sscanf (teststr, "%s is a %s")
@xresult{} 1lonelynumber

sscanf (teststr, "%g is a %s")
@xresult{}
     1
   108
   111
   110
   101
   108
   121

[a, b, c] = sscanf ("1 is a lonely number", "%g is a %s %s", "C")
@xresult{} a =  1
@xresult{} b = lonely
@xresult{} c = number
@end group
@end example

When a @dfn{matching failure} occurs, @code{scanf} returns immediately,
leaving the first non-matching character as the next character to be
read from the stream, and @code{scanf} returns all the items that were
successfully converted.
@cindex matching failure, in @code{scanf}

The formatted input functions are not used as frequently as the
formatted output functions.  Partly, this is because it takes some care
to use them properly.  Another reason is that it is difficult to recover
from a matching error.

The specific flags and modifiers that are permitted in the template string
and their interpretation are all described in more detail in the following
sections.

@node Input Conversion Syntax
@subsection Input Conversion Syntax

A @code{scanf} template string is a string that contains ordinary
multibyte characters interspersed with conversion specifications that
start with @samp{%}.

Any whitespace character in the template causes any number of whitespace
characters in the input stream to be read and discarded.  The whitespace
characters that are matched need not be exactly the same whitespace
characters that appear in the template string.  For example, write
@samp{ , } in the template to recognize a comma with optional whitespace
before and after.

Other characters in the template string that are not part of conversion
specifications must match characters in the input stream exactly; if
this is not the case, a matching failure occurs.

The conversion specifications in a @code{scanf} template string
have the general form:

@example
% @var{flags} @var{width} @var{type} @var{conversion}
@end example

In more detail, an input conversion specification consists of an initial
@samp{%} character followed in sequence by:

@itemize @bullet
@item
An optional @dfn{flag character} @samp{*}, which says to ignore the text
read for this specification.  When @code{scanf} finds a conversion
specification that uses this flag, it reads input as directed by the
rest of the conversion specification, but it discards this input, does
not return any value, and does not increment the count of
successful assignments.
@cindex flag character (@code{scanf})

@item
An optional decimal integer that specifies the @dfn{maximum field
width}.  Reading of characters from the input stream stops either when
this maximum is reached or when a non-matching character is found,
whichever happens first.  Most conversions discard initial whitespace
characters, and these discarded characters don't count towards the
maximum field width.  Conversions that do not discard initial whitespace
are explicitly documented.
@cindex maximum field width (@code{scanf})

@item
An optional type modifier character.  This character is ignored by
Octave's @code{scanf} function, but is recognized to provide
compatibility with the C language @code{scanf}.

@item
A character that specifies the conversion to be applied.
@end itemize

The exact options that are permitted and how they are interpreted vary
between the different conversion specifiers.  See the descriptions of the
individual conversions in @ref{Table of Input Conversions} for
information about the particular options that they allow.

@node Table of Input Conversions
@subsection Table of Input Conversions
@cindex input conversions, for @code{scanf}

Here is a table that summarizes the various conversion specifications:

@table @asis
@item @samp{%d}
Matches an optionally signed integer written in decimal.
@xref{Numeric Input Conversions}.

@item @samp{%i}
Matches an optionally signed integer in any of the formats that the C
language defines for specifying an integer constant.
@xref{Numeric Input Conversions}.

@item @samp{%o}
Matches an unsigned integer written in octal radix.
@xref{Numeric Input Conversions}.

@item @samp{%u}
Matches an unsigned integer written in decimal radix.
@xref{Numeric Input Conversions}.

@item @samp{%x}, @samp{%X}
Matches an unsigned integer written in hexadecimal radix.
@xref{Numeric Input Conversions}.

@item @samp{%e}, @samp{%f}, @samp{%g}, @samp{%E}, @samp{%G}
Matches an optionally signed floating-point number.
@xref{Numeric Input Conversions}.

@item @samp{%s}
Matches a string containing only non-whitespace characters.
@xref{String Input Conversions}.

@item @samp{%c}
Matches a string of one or more characters; the number of characters
read is controlled by the maximum field width given for the conversion.
@xref{String Input Conversions}.

@item @samp{%%}
This matches a literal @samp{%} character in the input stream.  No
corresponding argument is used.
@end table

If the syntax of a conversion specification is invalid, the behavior is
undefined.  If there aren't enough function arguments provided to supply
addresses for all the conversion specifications in the template strings
that perform assignments, or if the arguments are not of the correct
types, the behavior is also undefined.  On the other hand, extra
arguments are simply ignored.

@node Numeric Input Conversions
@subsection Numeric Input Conversions

This section describes the @code{scanf} conversions for reading numeric
values.

The @samp{%d} conversion matches an optionally signed integer in decimal
radix.

The @samp{%i} conversion matches an optionally signed integer in any of
the formats that the C language defines for specifying an integer
constant.

For example, any of the strings @samp{10}, @samp{0xa}, or @samp{012}
could be read in as integers under the @samp{%i} conversion.  Each of
these specifies a number with decimal value @code{10}.

The @samp{%o}, @samp{%u}, and @samp{%x} conversions match unsigned
integers in octal, decimal, and hexadecimal radices, respectively.

The @samp{%X} conversion is identical to the @samp{%x} conversion.  They
both permit either uppercase or lowercase letters to be used as digits.

By default, integers are read as 32-bit quantities.  With the @samp{h}
modifier, 16-bit integers are used, and with the @samp{l} modifier,
64-bit integers are used.

The @samp{%e}, @samp{%f}, @samp{%g}, @samp{%E}, and @samp{%G} conversions
match optionally signed floating-point numbers.  All five conversion
specifications behave identically, and will read in numerical values of
any floating point display style.

@node String Input Conversions
@subsection String Input Conversions

This section describes the @code{scanf} input conversions for reading
string and character values: @samp{%s} and @samp{%c}.

The @samp{%c} conversion is the simplest: it matches a fixed number of
characters, always.  The maximum field with says how many characters to
read; if you don't specify the maximum, the default is 1.  This
conversion does not skip over initial whitespace characters.  It reads
precisely the next @var{n} characters, and fails if it cannot get that
many.

The @samp{%s} conversion matches a string of non-whitespace characters.
It skips and discards initial whitespace, but stops when it encounters
more whitespace after having read something.

For example, reading the input:

@example
 hello, world
@end example

@noindent
with the conversion @samp{%10c} produces @qcode{" hello, wo"}, but
reading the same input with the conversion @samp{%10s} produces
@qcode{"hello,"}.

@node Binary I/O
@subsection Binary I/O

Octave can read and write binary data using the functions @code{fread}
and @code{fwrite}, which are patterned after the standard C functions
with the same names.  They are able to automatically swap the byte order
of integer data and convert among the supported floating point formats
as the data are read.

@c fread libinterp/corefcn/file-io.cc
@anchor{XREFfread}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{val} =} fread (@var{fid})
@deftypefnx {} {@var{val} =} fread (@var{fid}, @var{size})
@deftypefnx {} {@var{val} =} fread (@var{fid}, @var{size}, @var{precision})
@deftypefnx {} {@var{val} =} fread (@var{fid}, @var{size}, @var{precision}, @var{skip})
@deftypefnx {} {@var{val} =} fread (@var{fid}, @var{size}, @var{precision}, @var{skip}, @var{arch})
@deftypefnx {} {[@var{val}, @var{count}] =} fread (@dots{})
Read binary data from the file specified by the file descriptor @var{fid}.

The optional argument @var{size} specifies the amount of data to read
and may be one of

@table @code
@item Inf
Read as much as possible, returning a column vector.

@item @var{nr}
Read up to @var{nr} elements, returning a column vector.

@item [@var{nr}, Inf]
Read as much as possible, returning a matrix with @var{nr} rows.  If the
number of elements read is not an exact multiple of @var{nr}, the last
column is padded with zeros.

@item [@var{nr}, @var{nc}]
Read up to @code{@var{nr} * @var{nc}} elements, returning a matrix with
@var{nr} rows.  If the number of elements read is not an exact multiple
of @var{nr}, the last column is padded with zeros.
@end table

@noindent
If @var{size} is omitted, a value of @code{Inf} is assumed.

The optional argument @var{precision} is a string specifying the type of
data to read and may be one of

@table @asis
@item @qcode{"uint8"} (default)
8-bit unsigned integer.

@item  @qcode{"int8"}
@itemx @qcode{"integer*1"}
8-bit signed integer.

@item  @qcode{"uint16"}
@itemx @qcode{"ushort"}
@itemx @qcode{"unsigned short"}
16-bit unsigned integer.

@item  @qcode{"int16"}
@itemx @qcode{"integer*2"}
@itemx @qcode{"short"}
16-bit signed integer.

@item  @qcode{"uint"}
@itemx @qcode{"uint32"}
@itemx @qcode{"unsigned int"}
@itemx @qcode{"ulong"}
@itemx @qcode{"unsigned long"}
32-bit unsigned integer.

@item  @qcode{"int"}
@itemx @qcode{"int32"}
@itemx @qcode{"integer*4"}
@itemx @qcode{"long"}
32-bit signed integer.

@item @qcode{"uint64"}
64-bit unsigned integer.

@item  @qcode{"int64"}
@itemx @qcode{"integer*8"}
64-bit signed integer.

@item  @qcode{"single"}
@itemx @qcode{"float"}
@itemx @qcode{"float32"}
@itemx @qcode{"real*4"}
32-bit floating point number.

@item  @qcode{"double"}
@itemx @qcode{"float64"}
@itemx @qcode{"real*8"}
64-bit floating point number.

@item  @qcode{"char"}
@itemx @qcode{"char*1"}
8-bit single character.

@item  @qcode{"uchar"}
@itemx @qcode{"unsigned char"}
8-bit unsigned character.

@item  @qcode{"schar"}
@itemx @qcode{"signed char"}
8-bit signed character.

@end table

@noindent
The default precision is @qcode{"uint8"}.

The @var{precision} argument may also specify an optional repeat
count.  For example, @samp{32*single} causes @code{fread} to read
a block of 32 single precision floating point numbers.  Reading in
blocks is useful in combination with the @var{skip} argument.

The @var{precision} argument may also specify a type conversion.
For example, @samp{int16=>int32} causes @code{fread} to read 16-bit
integer values and return an array of 32-bit integer values.  By
default, @code{fread} returns a double precision array.  The special
form @samp{*TYPE} is shorthand for @samp{TYPE=>TYPE}.

The conversion and repeat counts may be combined.  For example, the
specification @samp{32*single=>single} causes @code{fread} to read
blocks of single precision floating point values and return an array
of single precision values instead of the default array of double
precision values.

The optional argument @var{skip} specifies the number of bytes to skip
after each element (or block of elements) is read.  If it is not
specified, a value of 0 is assumed.  If the final block read is not
complete, the final skip is omitted.  For example,

@example
fread (f, 10, "3*single=>single", 8)
@end example

@noindent
will omit the final 8-byte skip because the last read will not be
a complete block of 3 values.

The optional argument @var{arch} is a string specifying the data format
for the file.  Valid values are

@table @asis
@item @qcode{"native"} or @qcode{"n"}
The format of the current machine.

@item @qcode{"ieee-be"} or @qcode{"b"}
IEEE big endian.

@item @qcode{"ieee-le"} or @qcode{"l"}
IEEE little endian.
@end table

If no @var{arch} is given the value used in the call to @code{fopen} which
created the file descriptor is used.  Otherwise, the value specified with
@code{fread} overrides that of @code{fopen} and determines the data format.

The output argument @var{val} contains the data read from the file.

The optional return value @var{count} contains the number of elements read.
@xseealso{@ref{XREFfwrite,,fwrite}, @ref{XREFfgets,,fgets}, @ref{XREFfgetl,,fgetl}, @ref{XREFfscanf,,fscanf}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c fwrite libinterp/corefcn/file-io.cc
@anchor{XREFfwrite}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{count} =} fwrite (@var{fid}, @var{data})
@deftypefnx {} {@var{count} =} fwrite (@var{fid}, @var{data}, @var{precision})
@deftypefnx {} {@var{count} =} fwrite (@var{fid}, @var{data}, @var{precision}, @var{skip})
@deftypefnx {} {@var{count} =} fwrite (@var{fid}, @var{data}, @var{precision}, @var{skip}, @var{arch})
Write data in binary form to the file specified by the file descriptor
@var{fid}.

The argument @var{data} is a matrix of values that are to be written to the
file.  The values are extracted in column-major order.

The remaining arguments @var{precision}, @var{skip}, and @var{arch} are
optional, and are interpreted as described for @code{fread}.

The output @var{count} is the number of data items successfully written.

Programming Note: The behavior of @code{fwrite} is undefined if the values in
@var{data} are too large to fit in the specified precision.
@xseealso{@ref{XREFfread,,fread}, @ref{XREFfputs,,fputs}, @ref{XREFfprintf,,fprintf}, @ref{XREFfopen,,fopen}}
@end deftypefn


@node Temporary Files
@subsection Temporary Files

Sometimes one needs to write data to a file that is only temporary.
This is most commonly used when an external program launched from
within Octave needs to access data.  When Octave exits all temporary
files will be deleted, so this step need not be executed manually.

@c mkstemp libinterp/corefcn/file-io.cc
@anchor{XREFmkstemp}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {[@var{fid}, @var{name}, @var{msg}] =} mkstemp ("@var{template}")
@deftypefnx {} {[@var{fid}, @var{name}, @var{msg}] =} mkstemp ("@var{template}", @var{delete})
Return the file descriptor @var{fid} corresponding to a new temporary file
with a unique name created from @var{template}.

The last six characters of @var{template} must be @qcode{"XXXXXX"} and
these are replaced with a string that makes the filename unique.  The file
is then created with mode read/write and permissions that are system
dependent (on GNU/Linux systems, the permissions will be 0600 for versions
of glibc 2.0.7 and later).  The file is opened in binary mode and with the
@w{@code{O_EXCL}}@ flag.

If the optional argument @var{delete} is supplied and is true, the file will
be deleted automatically when Octave exits.

If successful, @var{fid} is a valid file ID, @var{name} is the name of the
file, and @var{msg} is an empty string.  Otherwise, @var{fid} is -1,
@var{name} is empty, and @var{msg} contains a system-dependent error
message.
@xseealso{@ref{XREFtempname,,tempname}, @ref{XREFtempdir,,tempdir}, @ref{XREFP_tmpdir,,P_tmpdir}, @ref{XREFtmpfile,,tmpfile}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c tmpfile libinterp/corefcn/file-io.cc
@anchor{XREFtmpfile}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {[@var{fid}, @var{msg}] =} tmpfile ()
Return the file ID corresponding to a new temporary file with a unique
name.

The file is opened in binary read/write (@qcode{"w+b"}) mode and will be
deleted automatically when it is closed or when Octave exits.

If successful, @var{fid} is a valid file ID and @var{msg} is an empty
string.  Otherwise, @var{fid} is -1 and @var{msg} contains a
system-dependent error message.
@xseealso{@ref{XREFtempname,,tempname}, @ref{XREFmkstemp,,mkstemp}, @ref{XREFtempdir,,tempdir}, @ref{XREFP_tmpdir,,P_tmpdir}}
@end deftypefn


@c tempname libinterp/corefcn/file-io.cc
@anchor{XREFtempname}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{fname} =} tempname ()
@deftypefnx {} {@var{fname} =} tempname (@var{dir})
@deftypefnx {} {@var{fname} =} tempname (@var{dir}, @var{prefix})
Return a unique temporary filename as a string.

If @var{prefix} is omitted, a value of @qcode{"oct-"} is used.

If @var{dir} is also omitted, the default directory for temporary files
(@code{P_tmpdir}) is used.  If @var{dir} is provided, it must exist,
otherwise the default directory for temporary files is used.

Programming Note: Because the named file is not opened by @code{tempname},
it is possible, though relatively unlikely, that it will not be available
by the time your program attempts to open it.  If this is a concern,
@pxref{XREFtmpfile,,@code{tmpfile}}.
@xseealso{@ref{XREFmkstemp,,mkstemp}, @ref{XREFtempdir,,tempdir}, @ref{XREFP_tmpdir,,P_tmpdir}, @ref{XREFtmpfile,,tmpfile}}
@end deftypefn


@c tempdir libinterp/corefcn/file-io.cc
@anchor{XREFtempdir}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{dir} =} tempdir ()
Return the name of the host system's directory for temporary files.

The directory name is taken first from the environment variable @env{TMPDIR}.
If that does not exist, the environment variable @env{TMP} (and on Windows
platforms also with higher priority the environment variable @env{TEMP}) is
checked.  If none of those are set, the system default returned by
@code{P_tmpdir} is used.
@xseealso{@ref{XREFP_tmpdir,,P_tmpdir}, @ref{XREFtempname,,tempname}, @ref{XREFmkstemp,,mkstemp}, @ref{XREFtmpfile,,tmpfile}}
@end deftypefn


@c P_tmpdir libinterp/corefcn/file-io.cc
@anchor{XREFP_tmpdir}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{sys_tmpdir} =} P_tmpdir ()
Return the name of the host system's @strong{default} directory for
temporary files.

Programming Note: The value returned by @code{P_tmpdir} is always the
default location.  This value may not agree with that returned from
@code{tempdir} if the user has overridden the default with the @env{TMPDIR}
environment variable.
@xseealso{@ref{XREFtempdir,,tempdir}, @ref{XREFtempname,,tempname}, @ref{XREFmkstemp,,mkstemp}, @ref{XREFtmpfile,,tmpfile}}
@end deftypefn


@node EOF (End of File) and Errors
@subsection EOF (End of File) and Errors

Once a file has been opened its status can be acquired.  As an example
the @code{feof} functions determines if the end of the file has been
reached.  This can be very useful when reading small parts of a file
at a time.  The following example shows how to read one line at a time
from a file until the end has been reached.

@example
@group
filename = "myfile.txt";
fid = fopen (filename, "r");
while (! feof (fid) )
  text_line = fgetl (fid);
endwhile
fclose (fid);
@end group
@end example

@noindent
Note that in some situations it is more efficient to read the entire
contents of a file and then process it, than it is to read it line by
line.  This has the potential advantage of removing the loop in the
above code.

@c feof libinterp/corefcn/file-io.cc
@anchor{XREFfeof}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{status} =} feof (@var{fid})
Return 1 if an end-of-file condition has been encountered for the file
specified by file descriptor @var{fid} and 0 otherwise.

Note that @code{feof} will only return 1 if the end of the file has already
been encountered, not if the next read operation will result in an
end-of-file condition.
@xseealso{@ref{XREFfread,,fread}, @ref{XREFfrewind,,frewind}, @ref{XREFfseek,,fseek}, @ref{XREFfclear,,fclear}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c ferror libinterp/corefcn/file-io.cc
@anchor{XREFferror}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{msg} =} ferror (@var{fid})
@deftypefnx {} {[@var{msg}, @var{err}] =} ferror (@var{fid})
@deftypefnx {} {[@dots{}] =} ferror (@var{fid}, "clear")
Query the error status of the stream specified by file descriptor @var{fid}.

If an error condition exists then return a string @var{msg} describing the
error.  Otherwise, return an empty string @qcode{""}.

The second input @qcode{"clear"} is optional.  If supplied, the error
state on the stream will be cleared.

The optional second output is a numeric indication of the error status.
@var{err} is 1 if an error condition has been encountered and 0 otherwise.

Note that @code{ferror} indicates if an error has already occurred, not
whether the next operation will result in an error condition.
@xseealso{@ref{XREFfclear,,fclear}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c fclear libinterp/corefcn/file-io.cc
@anchor{XREFfclear}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {} fclear (@var{fid})
Clear the stream state for the file specified by the file descriptor
@var{fid}.
@xseealso{@ref{XREFferror,,ferror}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c freport libinterp/corefcn/file-io.cc
@anchor{XREFfreport}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {} freport ()
Print a list of which files have been opened, and whether they are open
for reading, writing, or both.

For example:

@example
@group
freport ()

     @print{}  number  mode  arch       name
     @print{}  ------  ----  ----       ----
     @print{}     0     r    ieee-le    stdin
     @print{}     1     w    ieee-le    stdout
     @print{}     2     w    ieee-le    stderr
     @print{}     3     r    ieee-le    myfile
@end group
@end example
@xseealso{@ref{XREFfopen,,fopen}, @ref{XREFfclose,,fclose}, @ref{XREFis_valid_file_id,,is_valid_file_id}}
@end deftypefn


@node File Positioning
@subsection File Positioning

Three functions are available for setting and determining the position of
the file pointer for a given file.

@c ftell libinterp/corefcn/file-io.cc
@anchor{XREFftell}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{pos} =} ftell (@var{fid})
Return the position of the file pointer as the number of characters from the
beginning of the file specified by file descriptor @var{fid}.
@xseealso{@ref{XREFfseek,,fseek}, @ref{XREFfrewind,,frewind}, @ref{XREFfeof,,feof}, @ref{XREFfopen,,fopen}}
@end deftypefn


@c fseek libinterp/corefcn/file-io.cc
@anchor{XREFfseek}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {@var{status} =} fseek (@var{fid}, @var{offset})
@deftypefnx {} {@var{status} =} fseek (@var{fid}, @var{offset}, @var{origin})
Set the file pointer to the location @var{offset} within the file @var{fid}.

The pointer is positioned @var{offset} characters from the @var{origin}, which
may be one of the predefined variables @w{@qcode{SEEK_SET}}@ (beginning),
@w{@qcode{SEEK_CUR}}@ (current position), or @w{@qcode{SEEK_END}}@ (end of file)
or strings @nospell{@qcode{"bof"}}, @nospell{@qcode{"cof"}}, or
@nospell{@qcode{"eof"}}.  If @var{origin} is omitted, @w{@qcode{SEEK_SET}}@ is
assumed.  @var{offset} may be positive, negative, or zero but not all
combinations of @var{origin} and @var{offset} can be realized.

@code{fseek} returns 0 on success and -1 on error.
@xseealso{@ref{XREFfskipl,,fskipl}, @ref{XREFfrewind,,frewind}, @ref{XREFftell,,ftell}, @ref{XREFfopen,,fopen}, @ref{XREFSEEK_SET,,SEEK_SET}, @ref{XREFSEEK_CUR,,SEEK_CUR}, @ref{XREFSEEK_END,,SEEK_END}}
@end deftypefn


@c SEEK_SET libinterp/corefcn/file-io.cc
@anchor{XREFSEEK_SET}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{fseek_origin} =} SEEK_SET ()
Return the numerical value to pass to @code{fseek} to position the file pointer
relative to the beginning of the file.
@xseealso{@ref{XREFSEEK_CUR,,SEEK_CUR}, @ref{XREFSEEK_END,,SEEK_END}, @ref{XREFfseek,,fseek}}
@end deftypefn


@c SEEK_CUR libinterp/corefcn/file-io.cc
@anchor{XREFSEEK_CUR}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{fseek_origin} =} SEEK_CUR ()
Return the numerical value to pass to @code{fseek} to position the file pointer
relative to the current position.
@xseealso{@ref{XREFSEEK_SET,,SEEK_SET}, @ref{XREFSEEK_END,,SEEK_END}, @ref{XREFfseek,,fseek}}
@end deftypefn


@c SEEK_END libinterp/corefcn/file-io.cc
@anchor{XREFSEEK_END}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn {} {@var{fseek_origin} =} SEEK_END ()
Return the numerical value to pass to @code{fseek} to position the file pointer
relative to the end of the file.
@xseealso{@ref{XREFSEEK_SET,,SEEK_SET}, @ref{XREFSEEK_CUR,,SEEK_CUR}, @ref{XREFfseek,,fseek}}
@end deftypefn


@c frewind libinterp/corefcn/file-io.cc
@anchor{XREFfrewind}
@html
<span style="display:block; margin-top:-4.5ex;">&nbsp;</span>
@end html


@deftypefn  {} {} frewind (@var{fid})
@deftypefnx {} {@var{status} =} frewind (@var{fid})
Move the file pointer to the beginning of the file specified by file
descriptor @var{fid}.

If an output @var{status} is requested then @code{frewind} returns 0 for
success, and -1 if an error is encountered.

Programming Note: @code{frewind} is equivalent to
@code{fseek (@var{fid}, 0, SEEK_SET)}.
@xseealso{@ref{XREFfseek,,fseek}, @ref{XREFftell,,ftell}, @ref{XREFfopen,,fopen}}
@end deftypefn


The following example stores the current file position in the variable
@code{marker}, moves the pointer to the beginning of the file, reads
four characters, and then returns to the original position.

@example
@group
marker = ftell (myfile);
frewind (myfile);
fourch = fgets (myfile, 4);
fseek (myfile, marker, SEEK_SET);
@end group
@end example
