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

       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 .