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`setbuf'--specify full buffering for a file or stream

     #include <stdio.h>
     void setbuf(FILE *FP, char *BUF);
`setbuf' specifies that output to the file or stream identified by FP
should be fully buffered.  All output for this file will go to a buffer
(of size `BUFSIZ', specified in ``stdio.h'').  Output will be passed on
to the host system only when the buffer is full, or when an input
operation intervenes.
   You may, if you wish, supply your own buffer by passing a pointer to
it as the argument BUF.  It must have size `BUFSIZ'.  You can also use
`NULL' as the value of BUF, to signal that the `setbuf' function is to
allocate the buffer.
You may only use `setbuf' before performing any file operation other
than opening the file.
   If you supply a non-null BUF, you must ensure that the associated
storage continues to be available until you close the stream identified
by FP.
`setbuf' does not return a result.
Both ANSI C and the System V Interface Definition (Issue 2) require
`setbuf'.  However, they differ on the meaning of a `NULL' buffer
pointer: the SVID issue 2 specification says that a `NULL' buffer
pointer requests unbuffered output.  For maximum portability, avoid
`NULL' buffer pointers.
   Supporting OS subroutines required: `close', `fstat', `isatty',
`lseek', `read', `sbrk', `write'.