setbuf(3S)                                             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;

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, then 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];

     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.



January 1992                                                    1

setbuf(3S)                                             setbuf(3S)



STATUS MESSAGES AND VALUES
     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.

     setbuf allows assignment of a new I/O buffer after the
     stream has been read (written) and if unflushed data remains
     in the original buffer.  This could lead to a loss of data
     error.

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






































2                                                    January 1992