_IOFBF
(void)setvbuf(uf, NULL, _IOFBF,
(void) setvbuf(fp, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
(void)setvbuf(fp, buf, buf ? _IOFBF : _IONBF, (size_t)size);
if ((mode != _IOFBF && mode != _IOLBF) || size > INT_MAX)
_nonblock_eagain(_IOFBF);
mode = _IOFBF;
mode = _IOFBF;
(void)setvbuf(fp1, NULL, _IOFBF, 65536);
(void)setvbuf(fp2, NULL, _IOFBF, 65536);
setvbuf(f, NULL, _IOFBF, B_size);