EOF and Errors (GNU Octave (version 9.3.0))

#### 14.2.18 End of File and Errors ¶

Once a file has been opened its status can be acquired. As an example the `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.

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

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.

: `status =` feof `(fid)` ¶

  Return 1 if an end-of-file condition has been encountered for the file specified by file descriptor fid and 0 otherwise.

  Note that `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.

  See also: fread, frewind, fseek, fclear, fopen.

: `msg =` ferror `(fid)` ¶
: `[msg, err] =` ferror `(fid)` ¶
: `[…] =` ferror `(fid, "clear")` ¶

  Query the error status of the stream specified by file descriptor fid.

  If an error condition exists then return a string msg describing the error. Otherwise, return an empty string `""`.

  The second input `"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. err is 1 if an error condition has been encountered and 0 otherwise.

  Note that `ferror` indicates if an error has already occurred, not whether the next operation will result in an error condition.

  See also: fclear, fopen.

: fclear `(fid)` ¶

  Clear the stream state for the file specified by the file descriptor fid.

  See also: ferror, fopen.

: freport `()` ¶

  Print a list of which files have been opened, and whether they are open for reading, writing, or both.

  For example:

      freport ()

           -|  number  mode  arch       name
           -|  ------  ----  ----       ----
           -|     0     r    ieee-le    stdin
           -|     1     w    ieee-le    stdout
           -|     2     w    ieee-le    stderr
           -|     3     r    ieee-le    myfile

  See also: fopen, fclose, is_valid_file_id.