setvbuf(3C)

NAME

     setbuf, setvbuf - assign buffering to a stream

SYNOPSIS

     #include <stdio.h>

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

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

DESCRIPTION

     The setbuf() function may be used after the  stream  pointed
     to  by stream (see intro(3)) is 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.
     The constant  BUFSIZ, defined in the <stdio.h> header, indi-
     cates the size of the array pointed to by buf.

     The setvbuf() function may be used after a stream is  opened
     but  before it is read or written.  The type argument deter-
     mines how  stream will be buffered. Legal values  for   type
     (defined in <stdio.h>) are:

     _IOFBF
           Input/output to be fully buffered.

     _IOLBF
           Output to  be  line  buffered;   the  buffer  will  be
           flushed when a NEWLINE is written, the buffer is full,
           or input is requested.

     _IONBF
           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.  The size argument specifies the size of the  buffer
     to  be  used.  If input/output is unbuffered,  buf and  size
     are ignored.

     For a further discussion of buffering, see stdio(3C).

RETURN VALUES

     If an illegal value for  type is provided, setvbuf() returns
     a non-zero value.   Otherwise, it returns 0.

USAGE

     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.

     When using setbuf(), buf should always be sized  using  BUF-
     SIZ. If the array pointed to by buf is larger than BUFSIZ, a
     portion of buf will not be used.  If  buf  is  smaller  than
     BUFSIZ, other memory may be unexpectedly overwritten.

     Parts of buf will be used for internal  bookkeeping  of  the
     stream and, therefore, buf will contain less than size bytes
     when full. It is recommended that  stdio(3C) be used to han-
     dle buffer allocation when using setvbuf().

ATTRIBUTES

     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    |_____________________________|_____________________________|
    | MT-Level                    | MT-Safe                     |
    |_____________________________|_____________________________|

SEE ALSO

     fopen(3C), getc(3C), malloc(3C), putc(3C), stdio(3C), attri-
     butes(5)