_xwrite
extern ssize_t _xwrite(FILE *iop, const void *buf, size_t nbytes);
if (_xwrite(iop, (char *)&uch, 1) != 1) {
while ((num_wrote = _xwrite(iop, base, (size_t)n)) != n) {
while ((num_wrote = _xwrite(iop, ptr, (size_t)count)) !=
while ((n = _xwrite(iop, data, (size_t)bytes)) !=
while ((n = _xwrite(iop, dptr, s)) != s) {