setbuf(S)                      6 January 1993                      setbuf(S)


 Name

    setbuf, setvbuf - assign buffering to a stream

 Syntax


    cc  . . .  -lc


    #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

    The setbuf function 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 is 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 is 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 is flushed when a
              new line 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 is 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.

 Return value

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

 Diagnostics

    The setvbuf may fail if:

    [EBADF]   The file descriptor underlying stream is not valid.


 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.

    The parameter order of the setvbuf function is altered by the -compat
    option of the cc(CP) command.

 See also

    fopen(S), getc(S), malloc(S), putc(S), stdio(S)

 Standards conformance

    setbuf is conformant with:
    AT&T SVID Issue 2;
    X/Open Portability Guide, Issue 3, 1989;
    ANSI X3.159-1989 Programming Language -- C;
    Intel386 Binary Compatibility Specification, Edition 2 (iBCSe2);
    IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C
    Language] (ISO/IEC 9945-1); and NIST FIPS 151-1.

    setvbuf is conformant with:
    AT&T SVID Issue 2;
    X/Open Portability Guide, Issue 3, 1989; and
    ANSI X3.159-1989 Programming Language -- C.