# setbuf

## NAME



           setbuf, setbuffer, setlinebuf, setvbuf - stream buffering
           operations
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#include <stdio.h>**
    
           **int setvbuf(** size_t size;
                       **FILE *restrict** _stream_**, char** _buf_**[restrict** _size_**],**
                       **int** _mode_**, size_t** _size_**);**
    
           **void setbuf(FILE *restrict** _stream_**, char *restrict** _buf_**);**
           **void setbuffer(** size_t size;
                       **FILE *restrict** _stream_**, char** _buf_**[restrict** _size_**],**
                       **size_t** _size_**);**
           **void setlinebuf(FILE ***_stream_**);**
    
       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**(), **setlinebuf**(), │ Thread safety │ MT-Safe │
           │ **setvbuf**()                            │               │         │
           └──────────────────────────────────────┴───────────────┴─────────┘
    


## STANDARDS



           **setbuf**()
           **setvbuf**()
                  C11, POSIX.1-2008.
    


## CAVEATS



           POSIX notes that the value of _errno_ is unspecified after a call to
           **setbuf**() and further notes that, since the value of _errno_ is not
           required to be unchanged after a successful call to **setbuf**(),
           applications should instead use **setvbuf**() in order to detect
           errors.
    


## 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(stdout, buf);
               printf("Hello, world!\n");
               return 0;
           }
    


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