NAME

setbuf — assign buffering to a stream

SYNOPSIS

#include <stdio.h>

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


DESCRIPTION

^[CX] The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2024 defers to the ISO C standard.

Except that it returns no value, the function call:

setbuf(stream, buf)

shall be equivalent to:

setvbuf(stream, buf, _IOFBF, BUFSIZ)

if buf is not a null pointer, or to:

setvbuf(stream, buf, _IONBF, BUFSIZ)

if buf is a null pointer.

RETURN VALUE

The setbuf() function shall not return a value.

ERRORS

Although the setvbuf() interface may set errno in defined ways, the value of errno after a call to setbuf() is unspecified.

EXAMPLES

None.

APPLICATION USAGE

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.

With setbuf(), allocating a buffer of BUFSIZ bytes does not necessarily imply that all of BUFSIZ bytes are used for the buffer area.

Since errno is not required to be unchanged on success, in order to correctly detect and possibly recover from errors, applications should use setvbuf() instead of setbuf().

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

2.5 Standard I/O Streams, fopen, setvbuf

XBD <stdio.h>

CHANGE HISTORY

First released in Issue 1. Derived from Issue 1 of the SVID.

Issue 6

The prototype for setbuf() is updated for alignment with the ISO/IEC 9899:1999 standard.

Issue 7

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0546 [397], XSH/TC1-2008/0547 [397], and XSH/TC1-2008/0548 [14] are applied.