setvbuf()

Associate a buffer with a stream

Synopsis:

#include <stdio.h>

int setvbuf( FILE *fp,
             char *buf,
             int mode,
             size_t size );

Arguments:

fp

The stream that you want to associate with a buffer.

buffer

NULL, or a pointer to the buffer; see below.

mode

How you want the stream to be buffered:

_IOFBF — input and output are fully buffered.
_IOLBF — output is line buffered (i.e., the buffer is flushed when a newline character is written, when the buffer is full, or when input is requested).
_IONBF — input and output are completely unbuffered.

size

The size of the buffer.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The setvbuf() function associates a buffer with the stream designated by fp. If you want to call setvbuf(), you must call it after opening the stream, but before doing any reading, writing, or seeking.

If buf isn't NULL, the buffer it points to is used instead of an automatically allocated buffer.

Note: (QNX Neutrino 6.6 or later) As a QNX Neutrino extension, you can use the STDIO_DEFAULT_BUFSIZE environment variable to override BUFSIZ as the default buffer size for stream I/O. The value of STDIO_DEFAULT_BUFSIZE must be greater than that of BUFSIZ. For more information, see “Adjusting the buffer size” in the entry for fopen().

Returns:

0: Success.
EINVAL: The mode argument isn't valid.
ENOMEM: The buf argument is NULL, size isn't 0, and there isn't enough memory available to allocate a buffer.

Examples:

#include <stdio.h>
#include <stdlib.h>

int main( void )
{
    char *buf;
    FILE *fp;

    fp = fopen( "file", "r" );
    buf = malloc( 1024 );
    setvbuf( fp, buf, _IOFBF, 1024 );
    
    /* work with fp */
    ...
    
    fclose( fp );

    /* This is OUR buffer, so we have
     * to free it.  Do that AFTER
     * you've closed the file.
     */

    free( buf );
    return EXIT_SUCCESS;
}

Classification:

ANSI, POSIX 1003.1

Safety:
Cancellation point	No
Interrupt handler	No
Signal handler	No
Thread	Yes