GNU Octave: EOF and Errors

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#### 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.

Built-in Function: feof (fid)

  Return 1 if an end-of-file condition has been encountered for a given file and 0 otherwise. Note that it 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, fopen.

Built-in Function: [err, msg] = ferror (fid)
Built-in Function: [err, msg] = ferror (fid, "clear")

  Return 1 if an error condition has been encountered for the file ID fid and 0 otherwise. Note that it will only return 1 if an error has already been encountered, not if the next operation will result in an error condition.

  The second argument is optional. If it is supplied, also clear the error condition.

  See also: fclear, fopen.

Built-in Function: fclear (fid)

  Clear the stream state for the specified file.

  See also: fopen.

Built-in Function: 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  name
           -|
           -|       0     r  stdin
           -|       1     w  stdout
           -|       2     w  stderr
           -|       3     r  myfile

  See also: fopen, fclose.

Next: File Positioning, Previous: Temporary Files, Up: C-Style I/O Functions [Contents][Index]