1/* DUP.C: This program uses the variable old to save
2 * the original stdout. It then opens a new file named
3 * new and forces stdout to refer to it. Finally, it
4 * restores stdout to its original state.
5 */
6 
7#include <io.h>
8#include <stdlib.h>
9#include <stdio.h>
10 
11void main( void )
12{
13   int old;
14   FILE *new;
15 
16   old = dup( 1 );   /* "old" now refers to "stdout" */
17                      /* Note:  file handle 1 == "stdout" */
18   if( old == -1 )
19   {
20      perror( "dup( 1 ) failure" );
21      exit( 1 );
22   }
23   write( old, "This goes to stdout first\r\n", 27 );
24   if( ( new = fopen( "data", "w" ) ) == NULL )
25   {
26      puts( "Can't open file 'data'\n" );
27      exit( 1 );
28   }
29 
30   /* stdout now refers to file "data" */
31   if( -1 == dup2(fileno( new ), 1 ) )
32   {
33      perror( "Can't dup2 stdout" );
34      exit( 1 );
35   }
36   puts( "This goes to file 'data'\r\n" );
37 
38   /* Flush stdout stream buffer so it goes to correct file */
39   fflush( stdout );
40   fclose( new );
41 
42   /* Restore original stdout */
43   dup2( old, 1 );
44   puts( "This goes to stdout\n" );
45   puts( "The file 'data' contains:" );
46   system( "type data" );
47}
48