Как подменить дочернему процессу стандартные потоки ввода/вывода?

// crt_pipe.c
/* This program uses the _pipe function to pass streams of
 * text to spawned processes.
 */
 
#include <stdlib.h>
#include <stdio.h>
#include <io.h>
#include <fcntl.h>
#include <process.h>
#include <math.h>
 
enum PIPES { READ, WRITE }; /* Constants 0 and 1 for READ and WRITE */
#define NUMPROBLEM 8
 
int main( int argc, char *argv[] )
{
 
   int fdpipe[2];
   char hstr[20];
   int pid, problem, c;
   int termstat;
 
   /* If no arguments, this is the spawning process */
   if( argc == 1 )
   {
 
      setvbuf( stdout, NULL, _IONBF, 0 );
 
      /* Open a set of pipes */
      if( _pipe( fdpipe, 256, O_BINARY ) == -1 )
          exit( 1 );
 
 
      /* Convert pipe read descriptor to string and pass as argument 
       * to spawned program. Program spawns itself (argv[0]).
       */
      itoa( fdpipe[READ], hstr, 10 );
      if( ( pid = spawnl( P_NOWAIT, argv[0], argv[0], 
            hstr, NULL ) ) == -1 )
          printf( "Spawn failed" );
 
      /* Put problem in write pipe. Since spawned program is 
       * running simultaneously, first solutions may be done 
       * before last problem is given.
       */
      for( problem = 1000; problem <= NUMPROBLEM * 1000; problem += 1000)
      {
 
         printf( "Son, what is the square root of %d?\n", problem );
         write( fdpipe[WRITE], (char *)&problem, sizeof( int ) );
 
      }
 
      /* Wait until spawned program is done processing. */
      _cwait( &termstat, pid, WAIT_CHILD );
      if( termstat & 0x0 )
         printf( "Child failed\n" );
 
 
      close( fdpipe[READ] );
      close( fdpipe[WRITE] );
 
   }
 
   /* If there is an argument, this must be the spawned process. */
   else
   {
 
      /* Convert passed string descriptor to integer descriptor. */
      fdpipe[READ] = atoi( argv[1] );
 
      /* Read problem from pipe and calculate solution. */
      for( c = 0; c < NUMPROBLEM; c++ )
      {
 
        read( fdpipe[READ], (char *)&problem, sizeof( int ) );
        printf( "Dad, the square root of %d is %3.2f.\n",
                 problem, sqrt( ( double )problem ) );
 
      }
   }
}