Programming

int closen(int *fd, int len)
{
        while((--len) >= 0) close(fd[len]);
}

int main(void)
{
        pid_t proca, procb, scanner;
        int pipes[8];
        int from_proca, to_proca, from_procb, to_procb;
        pipe(pipes); pipe(pipes+2); pipe(pipes+4); pipe(pipes+6);

        proca=fork();
        if(proca == 0)
        {
                 dup2(pipes[(0*2)+0], STDIN_FILENO);
                 dup2(pipes[(1*2)+1], STDOUT_FILENO);

                 closeall(pipes, 8);
                 exec(...);
                 exit(1);
        }

        procb=fork();
        if(procb == 0)
        {
                 dup2(pipes[(2*2)+0], STDIN_FILENO);
                 dup2(pipes[(3*2)+1], STDOUT_FILENO);
                 closeall(pipes, 8);
                 exec(...);
                 exit(1);
        }

        from_proca=pipes[(1*2)+0;
        to_proca=pipes[(0*2)+1];
        from_procb=pipes[(3*2)+0;
        to_procb=pipes[(2*2)+1];

        scanner=fork();
        if(scanner == 0)
        {
                dup2(pipes[(1*2)+0], 10); // From proca
                dup2(pipes[(0*2)+1], 11); // To proca
                dup2(pipes[(3*2)+0], 12); // From procb
                dup2(pipes[(2*2)+1], 13); // To procb
                closen(pipes, 8);
                // You will have to tell the scanner process which FD's to use somehow
                exec(...);
                exit(1);
        }

        closen(pipes, 8);
}