writefn
int (*writefn)(void *, const char *, int);
writefn = _fopencookie_write;
writefn = NULL;
fp = funopen(thunk, readfn, writefn, _fopencookie_seek,
int (*writefn)(void *, const char *, int),
if (writefn == NULL) { /* illegal */
if (writefn == NULL)
fp->_write = writefn;
ATF_REQUIRE((f = fwopen(&s, writefn)) != NULL);
ATF_REQUIRE((f = fwopen(&s, writefn)) != NULL);