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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
       terminal  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 function 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 only be used 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, (char *) 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 3.35 of the Linux man-pages project.  A  description  of  the
       project,  and information about reporting bugs, can be found at http://man7.org/linux/man-
       pages/.