SETBUF

Section: C Library Functions (3)
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BSD mandoc
BSD 4

NAME

setbuf setbuffer setlinebuf setvbuf - stream buffering operations

SYNOPSIS

Fd #include <stdio.h> Ft void Fn setbuf FILE *stream char *buf Ft void Fn setbuffer FILE *stream char *buf size_t size Ft int Fn setlinebuf FILE *stream Ft int Fn setvbuf FILE *stream char *buf int mode size_t size

DESCRIPTION

The three types of buffering available are 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 output or input is read from any stream attached to a terminal device (typically stdin). 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 always unbuffered.

The Fn setvbuf function may be used to alter the buffering behavior of a stream. The Fa mode parameter must be one of the following three macros:

_IONBF: unbuffered
_IOLBF: line buffered
_IOFBF: fully buffered

The Fa 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 Fa buf argument should point to a buffer at least Fa size bytes long; this buffer will be used instead of the current buffer. (If the Fa size argument is not zero but Fa 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 Fn 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 Fn setvbuf . Except for the lack of a return value, the Fn setbuf function is exactly equivalent to the call

"setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);"

The Fn 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 Fn setlinebuf function is exactly equivalent to the call:

"setvbuf(stream, (char *)NULL, _IOLBF, 0);"

RETURN VALUES

The Fn 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 Fn setlinebuf function returns what the equivalent Fn setvbuf would have returned.

STANDARDS

The Fn setbuf and Fn setvbuf functions conform to St -ansiC .

BUGS

The Fn setbuffer and Fn setlinebuf functions are not portable to versions of BSD before BSD 4.2 On BSD 4.2 and BSD 4.3 systems, Fn setbuf always uses a suboptimal buffer size and should be avoided.

This document was created by man2html, using the manual pages.
Time: 19:41:58 GMT, December 25, 2022