x                  The character written to the file. Indicates
                       success.
    WEOF               Indicates an output error. The function sets
                       errno to the following:

                       o  EILSEQ - Invalid wide-character code
                          detected.

                       The function can also set errno to the
                       following as a result of errors returned from
                       the I/O subsystem:

                       o  EBADF - The file descriptor is not valid.

                       o  EIO - I/O error.

                       o  ENOSPC - No free space on the device
                          containing the file.

                       o  ENXIO - Device does not exist.

                       o  EPIPE - Broken pipe.

                       o  ESPIPE - Illegal seek in a file opened for
                          append.

                       o  EVMSERR - Nontranslatable OpenVMS error.
                          vaxc$errno contains the OpenVMS error code.
                          This indicates that an I/O error occurred
                          for which there is no equivalent C error
                          code.