SETBUF(3S)                           BSD                            SETBUF(3S)



NAME
     setbuf, setbuffer, setlinebuf, setvbuf - 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;

     int setvbuf(stream, buf, type, size)
     FILE *stream;
     char *buf;
     int mode;
     size_t 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)) can be
     used to force the block out early.  Normally all files are block
     buffered.  A buffer is obtained from malloc(3) 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:

          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 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.

     setvbuf may be used only after the stream pointed to by stream has been
     associated with an open file and before any other operation is performed

     on the stream.  mode determines how stream is buffered:

     _IOFBF   causes input/output to be fully buffered.

     _IOLBF   causes input/output to be line buffered.

     _IONBF   causes input/output to be unbuffered.

     If buf is not a null pointer, the array it points to may be used instead
     of a buffer allocated by setvbuf.  size specifies the size of the array.
     Its contents at any time are indeterminate.

SEE ALSO
     fopen(3S), getc(3S), putc(3S), malloc(3), fclose(3S), puts(3S),
     printf(3S), fread(3S)

DIAGNOSTICS
     setvbuf returns zero on success, or nonzero if an invalid value is given
     for mode or if the request cannot be honored.

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

     The setbuffer and setlinebuf functions are not portable to non-4.2BSD
     versions of the UNIX operating system.  On 4.2BSD and 4.3BSD systems,
     setbuf always uses a suboptimal buffer size and should be avoided.
     setbuffer is not usually needed as the default file I/O buffer sizes are
     optimal.