Trouble with pipe function

From: Craig Bumpstead (cbumpste_at_yahoo.com.au)
Date: 10/31/04 

Date: Sun, 31 Oct 2004 12:32:26 +1100

Hi,

I am having trouble with the pipe function.
Currently I can list the contents of a directory via readdir(), but
trying to get the pipe to work is difficult.

It just doesn't return anything?

I am not sure what I am doing wrong.

What is also difficult is debugging a multiprocess program. Any hints
would be great.
The target OS is unix, so that cuts out MS debuggers.

Cheers,
Craig

#include <dirent.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
#include <sys/types.h>
#include <wait.h>
#include <fcntl.h>
#include <signal.h>

int main()
{

int cmdPipe = 1;
int pipePos = 1;

char *cmdVarTwo = "sort";
char *cmdVarThree;
struct dirent *dirLIST;
DIR *userDIR;
char *currentDIR = ".";

int pipeDes[2];
int status = 0;
char *cmdSwitch[2];

pid_t pid1, pid2;

if( cmdPipe == 1 )
{
  if( pipePos == 1 )
    {
    if( pipe( pipeDes ) == -1 )
      {
        perror("Error creating pipe.\n");
        return 0;
      }
        
      switch( pid1 = fork() )
        {
        case -1:
           perror("Error creatign the fork");

        case 0:
           break;

        default:
           wait( &status);
           return 0;
        }
                
         pid2 = fork();
                
        switch( pid2 )
           {
            case -1:
                perror("Unable to fork the process.\n");
                exit(1);

            case 0:
                dup2( pipeDes[1], 1 );
                close( pipeDes[0] );
                close( pipeDes[1] );
                        
                 if((userDIR = opendir( currentDIR )) == NULL )
                   return (-1);

                while( (dirLIST = readdir(userDIR)))
                     {
                        if( dirLIST->d_ino != 0)
                          {
                              printf("%s\n", dirLIST->d_name);
                          }
                    }
                exit(1);

            default:
                dup2( pipeDes[0], 0 );
                                
                close( pipeDes[0] );
                close( pipeDes[1] );
                cmdSwitch[0] = cmdVarThree;
                                
                execvp( cmdVarTwo, cmdSwitch );
                wait(( int *)0 );
                /*perror("Parent exiting:");*/
                exit(1);
                /*return 0;*/

           }
        }
}

return 0;
}

Relevant Pages