libc.info: setvbuf

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`setvbuf'--specify file or stream buffering

*Synopsis*
     #include <stdio.h>
     int setvbuf(FILE *FP, char *BUF,
         int MODE, size_t SIZE);
   *Description*
Use `setvbuf' to specify what kind of buffering you want for the file
or stream identified by FP, by using one of the following values (from
`stdio.h') as the MODE argument:
`_IONBF'
     Do not use a buffer: send output directly to the host system for
     the file or stream identified by FP.
`_IOFBF'
     Use full output buffering: output will be passed on to the host
     system only when the buffer is full, or when an input operation
     intervenes.
`_IOLBF'
     Use line buffering: pass on output to the host system at every
     newline, as well as when the buffer is full, or when an input
     operation intervenes.
   Use the SIZE argument to specify how large a buffer you wish.  You
can supply the buffer itself, if you wish, by passing a pointer to a
suitable area of memory as BUF.  Otherwise, you may pass `NULL' as the
BUF argument, and `setvbuf' will allocate the buffer.
*Warnings*
You may only use `setvbuf' 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.
*Returns*
A `0' result indicates success, `EOF' failure (invalid MODE or SIZE can
cause failure).
*Portability*
Both ANSI C and the System V Interface Definition (Issue 2) require
`setvbuf'. 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.
   Both specifications describe the result on failure only as a nonzero
value.
   Supporting OS subroutines required: `close', `fstat', `isatty',
`lseek', `read', `sbrk', `write'.