Return_Values

   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.