SETBUF(3S)                           SysV                           SETBUF(3S)



NAME
     setbuf, setvbuf - assign buffering to a stream

SYNOPSIS
     #include <stdio.h>

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

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

DESCRIPTION
     setbuf may be used after a stream has been opened but before it is read
     or written.  It causes the array pointed to by buf to be used instead of
     an automatically allocated buffer.  If buf is the NULL pointer
     input/output will be completely unbuffered.

     A constant BUFSIZ, defined in the <stdio.h> header file, tells how big an
     array is needed:

          char buf[BUFSIZ];

     Except that it returns no value, the function call:

          setbuf(stream, buf);

     is equivalent to

          setvbuf(stream, buf,_IOFBF, BUFSIZ);

     if buf is not a null pointer, or to

          setvbuf(stream, buf,_IONBF, BUFSIZ);

     if buf is a null pointer.

     setvbuf may be used after a stream has been opened but before it is read
     or written.  type determines how stream will be buffered.  Legal values
     for type (defined in stdio.h) are:

     _IOFBF  causes input/output to be fully buffered.

     _IOLBF  causes output to be line buffered; the buffer will be flushed
             when a newline is written, the buffer is full, or input is
             requested.

     _IONBF  causes input/output to be completely unbuffered.

     If buf is not the NULL pointer, the array it points to will be used for
     buffering, instead of an automatically allocated buffer.  size specifies
     the size of the buffer to be used.  The constant BUFSIZ in <stdio.h> is
     suggested as a good buffer size.  If input/output is unbuffered, buf and
     size are ignored.

     By default, output to a terminal is line buffered and all other
     input/output is fully buffered.

SEE ALSO
     fopen(3S), getc(3S), malloc(3C), putc(3S), stdio(3S).

DIAGNOSTICS
     If an illegal value for type or size is provided, setvbuf returns a
     nonzero value. Otherwise, the value returned will be zero.

NOTES
     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.