4.55 setbuf—specify full buffering for a file or stream

Synopsis

#include <stdio.h>
void setbuf(FILE *fp, char *buf);

Description
setbuf specifies that output to the file or stream identified by fp should be fully buffered. All output for this file will go to a buffer (of size BUFSIZ, specified in ‘stdio.h’). Output will be passed on to the host system only when the buffer is full, or when an input operation intervenes.

You may, if you wish, supply your own buffer by passing a pointer to it as the argument buf. It must have size BUFSIZ. You can also use NULL as the value of buf, to signal that the setbuf function is to allocate the buffer.

Warnings
You may only use setbuf before performing any file operation other than opening the file.

If you supply a non-null buf, you must ensure that the associated storage continues to be available until you close the stream identified by fp.

Returns
setbuf does not return a result.

Portability
Both ANSI C and the System V Interface Definition (Issue 2) require setbuf. However, they differ on the meaning of a NULL buffer pointer: the SVID issue 2 specification says that a NULL buffer pointer requests unbuffered output. For maximum portability, avoid NULL buffer pointers.

Supporting OS subroutines required: close, fstat, isatty, lseek, read, sbrk, write.