setbuf(3S)             UNIX System V(C Development Set)              setbuf(3S)


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, sizet size);

DESCRIPTION
      setbuf may be used after a stream [see intro(3)] 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 will be completely unbuffered.

      While there is no limitation on the size of the buffer, the constant
      BUFSIZ, defined in the stdio.h header file, is typically a good buffer
      size:

            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.  Valid 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 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 is used for
      buffering, instead of an automatically allocated buffer.  size 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(3S).

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

DIAGNOSTICS
      If an invalid value for type is provided, setvbuf returns a non-zero
      value. Otherwise, it returns 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.


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setbuf(3S)             UNIX System V(C Development Set)              setbuf(3S)


      Parts of buf are used for internal bookkeeping of the stream and,
      therefore, buf contains less than size bytes when full.  It is
      recommended that the automatically allocated buffer is used when using
      setvbuf.


















































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