Help with piping program Post: 302112801

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Top Forums Programming Help with piping program Post 302112801 by PuppyHusher on Friday 30th of March 2007 12:26:31 PM

03-30-2007

Registered User

Never mind, I figured it out after some more searching and trying different things. Here's the working code, it can easily be changed to add more processes.

Code:

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>

void run_pipe(char **path, int read_fd, int write_fd);

int main (int argc, char **argv){
	
	int i;
	int pipe_count = 2;
	int proc_count = 3;
	int (*pipes)[2] = malloc(sizeof(*pipes) * pipe_count);

	char *cmd1 [] = {"cat",  "test2.c",    NULL};
	char *cmd2 [] = {"grep", "printf",     NULL};
	char *cmd3 [] = {"cut",  "-b", "1-6",  NULL};
       
	for (i = 0; i < pipe_count; i++)	pipe(pipes[i]);
        
    for (i = 0; i < proc_count; i++) {
		
		if (i == 0){						
            run_pipe(cmd1, 0, pipes[i][1]);
        }else if (i < proc_count - 1){		
           run_pipe(cmd2,	 pipes[i-1][0], pipes[i][1]);
        }else{								
             run_pipe(cmd3,	 pipes[i-1][0], 0);}
    }
}

void run_pipe(char **path, int read_fd, int write_fd){
        
	int pid = fork();

    if (pid){		//parent
		if (read_fd)	close(read_fd);
        if (write_fd)	close(write_fd);
        return;
    }

    if (read_fd)		dup2(read_fd , 0);
    if (write_fd)		dup2(write_fd, 1);

    execvp(*path, path);
}

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ares_process

ARES_PROCESS(3) 					     Library Functions Manual						   ARES_PROCESS(3)

NAME

       ares_process - Process events for name resolution

SYNOPSIS

       #include <ares.h>

       void ares_process(ares_channel channel, fd_set *read_fds,
       fd_set *write_fds)

       void ares_process_fd(ares_channel channel, ares_socket_t read_fd, ares_socket_t write_fd)

DESCRIPTION

       The  ares_process(3)  function handles input/output events and timeouts associated with queries pending on the name service channel identi-
       fied by channel.  The file descriptor sets pointed to by read_fds and write_fds should have file  descriptors  set  in  them  according	to
       whether the file descriptors specified by ares_fds(3) are ready for reading and writing.  (The easiest way to determine this information is
       to invoke select with a timeout no greater than the timeout given by ares_timeout(3) ).

       The ares_process function will invoke callbacks for pending queries if they complete successfully or fail.

       ares_process_fd(3) works the same way but acts and operates only on the specific file descriptors (sockets) you pass in	to  the  function.
       Use  ARES_SOCKET_BAD  for  "no action". This function is of course provided to allow users of c-ares to void select() in their applications
       and within c-ares.

   EXAMPLE
       The following code fragment waits for all pending queries on a channel to complete:

	      int nfds, count;
	      fd_set readers, writers;
	      struct timeval tv, *tvp;

	      while (1)
		{
		  FD_ZERO(&readers);
		  FD_ZERO(&writers);
		  nfds = ares_fds(channel, &readers, &writers);
		  if (nfds == 0)
		    break;
		  tvp = ares_timeout(channel, NULL, &tv);
		  count = select(nfds, &readers, &writers, NULL, tvp);
		  ares_process(channel, &readers, &writers);
		}

SEE ALSO

       ares_fds(3), ares_timeout(3)

AUTHOR

       Greg Hudson, MIT Information Systems
       Copyright 1998 by the Massachusetts Institute of Technology.

								   25 July 1998 						   ARES_PROCESS(3)

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