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():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _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.  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.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────┬───────────────┬─────────┐
       │Interface               │ Attribute     │ Value   │
       ├────────────────────────┼───────────────┼─────────┤
       │setbuf(), setbuffer(),  │ Thread safety │ MT-Safe │
       │setlinebuf(), setvbuf() │               │         │
       └────────────────────────┴───────────────┴─────────┘

CONFORMING TO

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

BUGS

       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

       stdbuf(1), fclose(3), fflush(3), fopen(3), fread(3), malloc(3), printf(3), puts(3)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A  description  of  the
       project,  information  about  reporting  bugs, and the latest version of this page, can be
       found at https://www.kernel.org/doc/man-pages/.