c - dup2 - Creating a piping program -

i write program replicate functionality of

program1 | program | programx

so redirect programx's output programx+1's input.

for sake of simplicity, start off 2 programs , single pipe.

in pseudocode, approach looks this:

1. create pipe communication between child1 , child2 2. fork parent create child1 , fork parent again create child2 3. close unneeded pipe ends in children 4. redirect output of execvp() child 1 write-end of pipe via dup2, child2 receives whatever program puts out 5. child2 reads pipe , receives output program of child1 6. execute execvp() received data 

so far good, here have:

#include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h>  #define read  0 #define write 1  int main(int argc, const char * argv[]) {      //create unidirectional pipe     int apipe[2];      if(pipe(apipe)){          perror("pipe call");         exit(exit_failure);      }      //create child 1 ("sender")     pid_t child_pid = fork();      if(child_pid < (pid_t)0)     {         perror("fork call failed");         exit(exit_failure);     }     else if(child_pid == (pid_t) 0){          //in child1         close(apipe[read]);          //get actual arguments argv array         const char **realargs = malloc(sizeof(char *) * (argc-1));          for(int i=1;i<argc;i++){              realargs[i-1] = argv[i];          }          //redirect standard output write-end of pipe         dup2(apipe[write], stdout_fileno);         close(apipe[write]);         execvp(argv[0], realargs);          //exec call failed         exit(exit_failure);        }       //parent     //create second child ("receiver")     pid_t child2_pid = fork();      if(child2_pid == (pid_t)0){          //close unneeded pipe end         close(apipe[write]);          char buffer[1024];         char **argv2 = malloc(sizeof(char *));          while (read(apipe[read], buffer, sizeof(buffer)) != 0)         {              argv2[0] = buffer;             printf("buffer = %s", buffer);             //execvp("sort", argv2);          }          close(apipe[read]);         exit(exit_success);      }      //close unneeded pipe ends, parent not need pipe     close(apipe[write]);     close(apipe[read]);      exit(exit_success);      return 0; } 

that achieves trying do, output in child2 seems write pipe again , results in writing own pipe. think, , may wrong here, (despite closing write end in child2) via printf writes own pipe (as redirected stdout write end of pipe) , reads again. output looks this

when run program parameters who , sort

myprog sort

i following output:

buffer = buffer = martine****** console apr 24 12:59

edit:

how set input sort command in execvp("sort", argsarr); ? sort takes in filename, how go ?