| SETBUF(3) | Library Functions Manual | SETBUF(3) | 
setbuf, setbuffer,
  setlinebuf, setvbuf —
#include <stdio.h>
void
  
  setbuf(FILE
    * restrict stream, char *
    restrict buf);
void
  
  setbuffer(FILE
    *stream, char *buf,
    size_t size);
int
  
  setlinebuf(FILE
    *stream);
int
  
  setvbuf(FILE
    * restrict stream, char *
    restrict buf, int
    mode, size_t
  size);
The default buffer settings can be overwritten per descriptor
    (STDBUFn, where
    n is the numeric value of the file descriptor
    represented by the stream), or for all descriptors
    (STDBUF). The environment variable value is a letter
    followed by an optional numeric value indicating the size of the buffer.
    Valid sizes range from 0B to 1MB. Valid letters are:
The function fflush(3) may be used to force the block out early. (See fclose(3).)
Normally all files are block buffered. When the first I/O operation occurs on a file, malloc(3) is called, and an optimally-sized buffer is obtained. If a stream refers to a terminal (as stdout normally does) it is line buffered. The standard error stream stderr is initially unbuffered.
The setvbuf() function may be used to
    alter the buffering behavior of a stream. The mode
    parameter must be one of the following three macros:
The size parameter may be given as zero to
    obtain deferred optimal-size buffer allocation as usual. If it is not zero,
    then except for unbuffered files, the buf argument
    should point to a buffer at least size bytes long;
    this buffer will be used instead of the current buffer. (If the
    size argument is not zero but
    buf is NULL, a buffer of the
    given size will be allocated immediately, and released on close. This is an
    extension to ANSI C; portable code should use a size of 0 with any
    NULL buffer.)
The setvbuf() function may be used at any
    time, but may have peculiar side effects (such as discarding input or
    flushing output) if the stream is ``active''. Portable applications should
    call it only once on any given stream, and before any I/O is performed.
The other three calls are, in effect, simply aliases for calls to
    setvbuf(). Except for the lack of a return value,
    the setbuf() function is exactly equivalent to the
    call
setvbuf(stream, buf, buf ? _IOFBF :
  _IONBF, BUFSIZ);The setbuffer() function is the same,
    except that the size of the buffer is up to the caller, rather than being
    determined by the default BUFSIZ. The
    setlinebuf() function is exactly equivalent to the
    call:
setvbuf(stream, (char *)NULL, _IOLBF,
  0);setvbuf() function returns 0 on success, or
  EOF if the request cannot be honored (note that the
  stream is still functional in this case).
The setlinebuf() function returns what the
    equivalent setvbuf() would have returned.
setbuf() and setvbuf()
  functions conform to ANSI X3.159-1989
  (“ANSI C89”).
setbuf() function first appeared in
  Version 7 AT&T UNIX. The
  setbuffer() function first appeared in
  4.1cBSD. The setlinebuf()
  function first appeared in 4.2BSD. The
  setvbuf() function first appeared in
  4.4BSD.
setbuf() function usually uses a suboptimal buffer
  size and should be avoided.
| June 4, 1993 | NetBSD 9.3 |