NAME

setbuf, setbuffer, setlinebuf − assign buffering to a stream

USAGE

#include <stdio.h>
 
setbuf(stream, buf) FILE *stream; char *buf;
 
setbuffer(stream, buf, size) FILE *stream; char *buf; int size;
 
setlinebuf(stream) FILE *stream;

DESCRIPTION

Three types of buffering are available: unbuffered, block-buffered, and line-buffered.  When an output stream is unbuffered, information appears on the destination file or terminal as soon as written; when it is block-buffered, many characters are saved up and written as a block; when it is line-buffered, characters are saved up until a newline is encountered or input is read from stdin.  Fflush (see fclose(3S)) may be used to force the block out early.  Normally, all files are block-buffered.  A buffer is obtained from malloc(3) upon the first getc(3S) or putc(3S) call on a file.  If the standard stream stdout refers to a terminal, the output is line-buffered.  The standard stream stderr is always unbuffered. 

Setbuf is used after a stream has been opened, but before it is read or written.  The character array buf is used instead of an automatically allocated buffer.  If buf is the constant pointer NULL, input/output will be completely unbuffered.  A manifest constant BUFSIZ tells how big an array is needed, as shown here.  char buf[BUFSIZ]; Setbuffer, an alternate form of setbuf, is used after a stream has been opened, but before it is read or written.  The character array buf whose size is determined by the size argument is used instead of an automatically allocated buffer.  If buf is the constant pointer NULL, input/output will be completely unbuffered. 

Setlinebuf is used to change stdout or stderr from block-buffered or unbuffered to line-buffered.  Unlike setbuf and setbuffer, it can be used at any time that the file descriptor is active. 

A file can be changed from unbuffered or line-buffered to block-buffered by using freopen (see fopen(3S)).  A file can be changed from block-buffered or line-buffered to unbuffered by using freopen followed by setbuf with a buffer argument of NULL. 

RELATED INFORMATION

fopen(3S), getc(3S), putc(3S), malloc(3), fclose(3S), puts(3S), printf(3S), fread(3S)