dup()

Arguments:

filedes

The file descriptor that you want to duplicate.

Library:

libc

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

Description:

The dup() function duplicates the file descriptor specified by filedes and returns the new file descriptor. The number of this new descriptor is the lowest available (i.e., not already open) file descriptor and it refers to the same open file description as the original and shares any locks.

dup_filedes = dup( filedes );

dup_filedes = fcntl( filedes, F_DUPFD, 0 );

The two file descriptors do not share file descriptor flags, so the close-on-exec flag (FD_CLOEXEC) for the duplicate descriptor is off.

Returns:

The new file descriptor for success, or -1 if an error occurs (errno is set).

Errors:

EBADF

The file descriptor, filedes, isn't a valid open file descriptor.

EMFILE

All file descriptors available to the process are currently open.

ENOSYS

The dup() function isn't implemented for the filesystem specified by filedes.

Examples:

#include <fcntl.h>
#include <unistd.h>
#include <sys/stat.h>
#include <stdlib.h>

int main( void )
{
    int filedes, dup_filedes;

    filedes = open( "file",
        O_WRONLY | O_CREAT | O_TRUNC,
        S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP );

    if( filedes != -1 ) {
        dup_filedes = dup( filedes );
        if( dup_filedes != -1 ) {
            /* process file */
            /* ... */

            close( dup_filedes );
        }
        close( filedes );
        
        return EXIT_SUCCESS;
    }
    
    return EXIT_FAILURE;
}

Classification:

POSIX 1003.1