dup2()
Duplicate a file descriptor, specifying the new descriptor number
Synopsis:
#include <unistd.h>
int dup2( int filedes,
int filedes2 );
Arguments:
- filedes
- The file descriptor that you want to duplicate.
- filedes2
- The number that you want to use for the new file descriptor.
Library:
libc
Use the -l c option to qcc to link against this library. This library is usually included automatically.
Description:
The dup2() function duplicates the file descriptor specified by filedes and returns the new file descriptor. The number of this new descriptor is filedes2 and it refers to the same open file description as the original and shares any locks. If a file already is opened with this descriptor number, the file is closed before the duplication is attempted, unless filedes2 is the same as filedes, in which case dup2() returns filedes2 without closing the file.
- references the same file or device
- has the same open mode (read and/or write)
- has an identical file position to the original (changing the position with one descriptor results in a changed position in the other)
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 value of filedes2 for success, or -1 if an error occurs (errno is set).
Errors:
- EBADF
- The filedes argument isn't a valid open file descriptor, or filedes2 is out of range.
- EINTR
- The function was interrupted by a signal.
- EMFILE
- All file descriptors available to the process are currently open.
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 = 4;
if( dup2( filedes, dup_filedes ) != -1 ) {
/* process file */
/* ... */
close( dup_filedes );
}
close( filedes );
return EXIT_SUCCESS;
}
return EXIT_FAILURE;
}
Classification:
| Safety: | |
|---|---|
| Cancellation point | No |
| Signal handler | Yes |
| Thread | Yes |