SETBUF(3)                           Linux Programmer's Manual                           SETBUF(3)



NAME
       setbuf, setbuffer, setlinebuf, setvbuf - stream buffering operations

SYNOPSIS
       #include <stdio.h>

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

       void setbuffer(FILE *stream, char *buf, size_t size);

       void setlinebuf(FILE *stream);

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

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setbuffer(), setlinebuf(): _BSD_SOURCE

DESCRIPTION
       The  three types of buffering available are unbuffered, block buffered, and line buffered.
       When an output stream is unbuffered, information appears on the destination file or termi-
       nal as soon as written; when it is block buffered many characters are saved up and written
       as a block; when it is line buffered characters are saved up until a newline is output  or
       input  is read from any stream attached to a terminal device (typically stdin).  The func-
       tion fflush(3) may be used to force the block out early.  (See fclose(3).)   Normally  all
       files  are  block  buffered.   When the first I/O operation occurs on a file, malloc(3) is
       called, and a buffer is obtained.  If a stream refers to a terminal  (as  stdout  normally
       does)  it  is  line  buffered.   The  standard error stream stderr is always unbuffered by
       default.

       The setvbuf() function may be used on any open stream to  change  its  buffer.   The  mode
       argument must be one of the following three macros:

              _IONBF unbuffered

              _IOLBF line buffered

              _IOFBF fully buffered

       Except for unbuffered files, the buf argument should point to a buffer at least size bytes
       long; this buffer will be used instead of the current buffer.   If  the  argument  buf  is
       NULL,  only the mode is affected; a new buffer will be allocated on the next read or write
       operation.  The setvbuf() function may be used only after opening a stream and before  any
       other operations have been performed on it.

       The other three calls are, in effect, simply aliases for calls to setvbuf().  The setbuf()
       function is exactly equivalent to the call

           setvbuf(stream, buf, buf ? _IOFBF : _IONBF, BUFSIZ);

       The setbuffer() function is the same, except that the size of the  buffer  is  up  to  the
       caller,  rather than being determined by the default BUFSIZ.  The setlinebuf() function is
       exactly equivalent to the call:

           setvbuf(stream, NULL, _IOLBF, 0);

RETURN VALUE
       The function setvbuf() returns 0 on success.  It  returns  nonzero  on  failure  (mode  is
       invalid or the request cannot be honored).  It may set errno on failure.

       The other functions do not return a value.

CONFORMING TO
       The setbuf() and setvbuf() functions conform to C89 and C99.

BUGS
       The  setbuffer()  and  setlinebuf()  functions  are not portable to versions of BSD before
       4.2BSD, and are available under Linux since libc 4.5.21.  On 4.2BSD  and  4.3BSD  systems,
       setbuf() always uses a suboptimal buffer size and should be avoided.

       You  must  make  sure that the space that buf points to still exists by the time stream is
       closed, which also happens at program termination.  For example, the following is invalid:

       #include <stdio.h>

       int
       main(void)
       {
           char buf[BUFSIZ];
           setbuf(stdin, buf);
           printf("Hello, world!\n");
           return 0;
       }

SEE ALSO
       fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)

COLOPHON
       This page is part of release 3.53 of the Linux man-pages project.  A  description  of  the
       project,     and    information    about    reporting    bugs,    can    be    found    at
       http://www.kernel.org/doc/man-pages/.



Linux                                       2012-08-03                                  SETBUF(3)