_IOFBF
setvbuf(stdout, buffer, _IOFBF, sizeof buffer);
setvbuf(stdout, obuf, _IOFBF, sizeof obuf);
setvbuf(stdout, outbuf, _IOFBF, sizeof outbuf);
(void) setvbuf(fp, buf, buf ? _IOFBF : _IONBF, BUFSIZ);
(void)setvbuf(fp, buf, buf ? _IOFBF : _IONBF, size);
if ((mode != _IOFBF && mode != _IOLBF) || size > INT_MAX)
(void) setvbuf(ofp, buf_ptr, buf_len, buf_len ? _IOFBF : _IOLBF);
(void) setvbuf(ofp, buf_ptr, buf_len ? _IOFBF : _IOLBF, buf_len);
errors += dotest(_IOFBF, iobuf, sizeof(iobuf));
case _IOFBF:
TEST_UNCHANGED(setvbuf(f, buffer, _IOFBF, BUFSIZ));
TEST_UNCHANGED(setvbuf(f, NULL, _IOFBF, 0));
setvbuf(stdin, iobuf, _IOFBF, iobufsiz);
setvbuf(stdout, stdoutbuf, _IOFBF, sizeof stdoutbuf);
(void)setvbuf(stdout, NULL, _IOFBF, 0);
setvbuf(stdout, NULL, _IOFBF, 0);
setvbuf(stderr, NULL, _IOFBF, 0);
setvbuf(fp, filebuf, _IOFBF, BUFSIZ);