merror tests the file access errors indicator

## Syntax

                err = merror([fd])
                [err, msg] = merror([fd])

## Arguments

fd

  a scalar: the `fd` parameter returned by the function `mopen` is used as a file descriptor (it's a positive integer). -1 stands for last opened file. The default value is -1.

err

  a scalar: an error status number of the most recent file I/O operation associated with the specified file.

  If the most recent I/O operation performed on the specified file was successful, the value of `msg` is empty and `merror` returns an `err` value of 0.

msg

  a string: an error string message.

## Description

The function `merror` is used to test the file access errors indicator returning non-zero if it is set. The error indicator can only be reset by the `mclearerr` function.

A nonzero `err` indicates that an error occurred in the most recent file I/O operation. The value of message is a string that can contain information about the nature of the error. If the message is not helpful, consult the C run-time library manual for your host operating system for further details.

## Examples

    fd = mopen(TMPDIR +'/filetxt.txt','wt');
    [err,msg] = merror(fd)
    if (err <> 0) then
      mprintf('Problem\n');
    end
    mclose(fd);

## See also

- mclearerr
- mclose
- mopen
- mput
- mget
- mgetstr
- mputstr
- meof
- mseek
- mtell