SETBUF(3S)              COMMAND REFERENCE              SETBUF(3S)



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

SYNOPSIS
     #include <stdio.h>

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

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

     setlinebuf(stream)
     FILE *stream;

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 always
     unbuffered.

     Setbuf is used after a stream has been opened but before it
     is read or written.  The character array buf is used instead
     of an automatically allocated buffer.  If buf is the
     constant pointer NULL, input/output will be completely
     unbuffered.  A manifest constant BUFSIZ tells how big an
     array is needed.  For example:

          char buf[BUFSIZ];

     Setbuffer, an alternate form of setbuf, is used after a
     stream has been opened but before it is read or written.
     The character array buf whose size is determined by the size
     argument is used instead of an automatically allocated
     buffer.  If buf is the constant pointer NULL, input/output
     will be completely unbuffered.

     Setlinebuf is used to change stdout or stderr from block
     buffered or unbuffered to line buffered.  Unlike setbuf and
     setbuffer it can be used at any time that the file



Printed 3/13/89                                                 1

SETBUF(3S)              COMMAND REFERENCE              SETBUF(3S)



     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.

CAVEATS
     The standard error stream should be line buffered by
     default.

     The setbuffer and setlinebuf functions are portable to
     4.2BSD systems only.

SEE ALSO
     fopen(3s), getc(3s), putc(3s), malloc(3c), fclose(3s),
     puts(3s), printf(3s), and fread(3s).





































Printed 3/13/89                                                 2

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