I/O buffering

Names specified here
Name	Description			Source	Availability
`_IOFBF`	Full-buffering flag	M		`<stdio.h>`	C89	C90	C95	C99	C11
`_IOLBF`	Line-buffering flag	M		`<stdio.h>`	C89	C90	C95	C99	C11
`_IONBF`	No-buffering flag	M		`<stdio.h>`	C89	C90	C95	C99	C11
`BUFSIZ`	Built-in buffer size for I/O	M		`<stdio.h>`	C89	C90	C95	C99	C11
`setbuf()`	Set stream buffer		(·)	`<stdio.h>`	C89	C90	C95	C99	C11
`setvbuf()`	Set stream buffer		(·)	`<stdio.h>`	C89	C90	C95	C99	C11

#include <stdio.h>
void setbuf(FILE *str,
            char *buf);
int setvbuf(FILE *str,
            char *buf,
            int mode,
            size_t sz);

setvbuf and setbuf set the buffering on a stream str that has just been opened. mode can have the following values:

Value of `mode`	Buffering mode
`_IOFBF`	full buffering
`_IOLBF`	line buffering
`_IONBF`	no buffering

buf may point to a buffer of sz bytes to be used, or it may be NULL, indicating that the function should allocate a buffer internally. setvbuf returns non-zero if mode is invalid, or it cannot otherwise change the stream's buffering.

BUFSIZ is the buffer size that setbuf assumes (lacking a parameter sz). setbuf(str, buf) is equivalent to setvbuf(str, NULL, _IONBF, BUFSIZ) if buf is NULL, or to setvbuf(str, buf, _IOFBF, BUFSIZ) otherwise. It also discards the return value. BUFSIZ is at least 256.