setbuf(S)

setbuf, setvbuf -- assign buffering to a stream

Syntax

cc . . . -lc

#include  <stdio.h>

void setbuf (stream, buf)
FILE *stream;
char *buf;

int setvbuf (stream, buf, type, size)
FILE *stream;
char *buf;
int type;
size_t size;

Description

setbuf- assign buffer to a stream

setvbuf- assign buffer after a stream has been opened

The setbuf function may be used after a stream has been opened but before it is read or written. It causes the array pointed to by buf to be used instead of an automatically allocated buffer. If buf is the NULL pointer, input/output is completely unbuffered.

A constant BUFSIZ, defined in the <stdio.h> header file, tells how big an array is needed:

   char buf[BUFSIZ];

setvbuf may be used after a stream has been opened but before it is read or written. type determines how stream is buffered. Legal values for type (defined in <stdio.h>) are:

_IOFBF: causes input/output to be fully buffered.
_IOLBF: causes output to be line buffered; the buffer is flushed when a new line is written, the buffer is full, or input is requested.
_IONBF: causes input/output to be completely unbuffered.

If buf is not the NULL pointer, the array it points to is used for buffering, instead of an automatically allocated buffer. size specifies the size of the buffer to be used. The constant BUFSIZ in <stdio.h> is suggested as a good buffer size. If input/output is unbuffered, buf and size are ignored.

By default, output to a terminal is line-buffered and all other input/output is fully buffered.

Return value

If an illegal value for type or size is provided, setvbuf returns a non-zero value. Otherwise, the value returned is zero.

Diagnostics

The setvbuf may fail if:

[EBADF]: The file descriptor underlying stream is not valid.

Notes

A common source of error is allocating buffer space as an ``automatic'' variable in a code block, and then failing to close the stream in the same block.

The parameter order of the setvbuf function is altered by the -compat option of the cc(CP) command.

Standards conformance

setbuf is conformant with:

X/Open Portability Guide, Issue 3, 1989 ;
ANSI X3.159-1989 Programming Language -- C ;
Intel386 Binary Compatibility Specification, Edition 2 (iBCSe2) ;
IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C Language] (ISO/IEC 9945-1) ; and NIST FIPS 151-1 .

setvbuf is conformant with:

X/Open Portability Guide, Issue 3, 1989 ; and
ANSI X3.159-1989 Programming Language -- C .