SETVBUF(3)                 POSIX Programmer's Manual                SETVBUF(3)



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

NAME
       setvbuf -- assign buffering to a stream

SYNOPSIS
       #include <stdio.h>

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

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.

       The setvbuf() function may be used after the stream pointed to by
       stream is associated with an open file but before any other operation
       (other than an unsuccessful call to setvbuf()) is performed on the
       stream. The argument type determines how stream shall be buffered, as
       follows:

        *  {_IOFBF} shall cause input/output to be fully buffered.

        *  {_IOLBF} shall cause input/output to be line buffered.

        *  {_IONBF} shall cause input/output to be unbuffered.

       If buf is not a null pointer, the array it points to may be used
       instead of a buffer allocated by setvbuf() and the argument size
       specifies the size of the array; otherwise, size may determine the size
       of a buffer allocated by the setvbuf() function. The contents of the
       array at any time are unspecified.

       For information about streams, see Section 2.5, Standard I/O Streams.

RETURN VALUE
       Upon successful completion, setvbuf() shall return 0. Otherwise, it
       shall return a non-zero value if an invalid value is given for type or
       if the request cannot be honored, and may set errno to indicate the
       error.

ERRORS
       The setvbuf() function may fail if:

       EBADF  The file descriptor underlying stream is not valid.

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

       Applications should note that many implementations only provide line
       buffering on input from terminal devices.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       Section 2.5, Standard I/O Streams, fopen(), setbuf()

       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 .



IEEE/The Open Group                  2017                           SETVBUF(3)
