SETBUF(3P)

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.1-2017 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.1-2017, <stdio.h>

COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 .