setbuf(3S)              (BSD Compatibility Package)              setbuf(3S)


   NAME
         setbuf, setbuffer, setlinebuf, setvbuf - assign buffering to a stream

   SYNOPSIS
         cc [ flag... ] file ... -lucb

         #include <stdio.h>

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

         setbuffer(stream, buf, size)
         FILE *stream;
         char *buf;
         int size;

         setlinebuf(stream)
         FILE *stream;

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

   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 encountered or input is read from stdin.  fflush
         (see fclose(3S)) may be used to force the block out early.  Normally
         all files are block buffered.  A buffer is obtained from malloc(3C)
         upon the first getc or putc(3S) on the file.  If the standard stream
         stdout refers to a terminal it is line buffered.  The standard stream
         stderr is unbuffered by default.

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

               char buf[BUFSIZ];

         setbuffer, an alternate form of setbuf, can be used after a stream
         has been opened but before it is read or written.  It uses the
         character array buf whose size is determined by the size argument
         instead of an automatically allocated buffer.  If buf is the NULL


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   setbuf(3S)              (BSD Compatibility Package)              setbuf(3S)


         pointer, input/output will be completely unbuffered.

         setvbuf can 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
                 fully buffers the input/output.

            _IOLBF
                 line buffers the output; the buffer will be flushed when a
                 NEWLINE is written, the buffer is full, or input is
                 requested.

            _IONBF
                 completely unbuffers the input/output.

         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.

         setlinebuf is used to change the buffering on a stream from block
         buffered or unbuffered to line buffered.  Unlike setbuf, setbuffer,
         and setvbuf, it can be used at any time that the file descriptor is
         active.

         A file can be changed from unbuffered or line buffered to block
         buffered by using freopen (see fopen(3S)).  A file can be changed
         from block buffered or line buffered to unbuffered by using freopen
         followed by setbuf with a buffer argument of NULL.

   NOTE
         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.

   SEE ALSO
         fclose(3S), fopen(3S), fread(3S), getc(3S), malloc(3C), printf(3S),
         putc(3S), puts(3S), setbuf(3S) in the Programmer's Reference Manual.

   RETURN VALUE
         If an illegal value for type or size is provided, setvbuf returns a
         non-zero value.  Otherwise, the value returned will be zero.










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