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setbuf(3p)

IEEE/The Open Group
2013

man-pages

Linux kernel and C library user-space interface documentation

man-pages-posix

POSIX Manual Pages

PROLOG

This manual page is part of the POSIX Programmer’s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

setbuf — assign buffering to a stream

SYNOPSIS

#include <stdio.h>

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

DESCRIPTION

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.1-2008 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.
The following sections are informative.

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

Section 2.5, Standard I/O Streams, fopen(), setvbuf()
The Base Definitions volume of POSIX.1-2008, <stdio.h>

COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
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