I am trying to find out how I can send output of one process into a child process. I have gone down a journey learning of file descriptors and pipes. I think I am almost there but am missing a key component.
This is what I have so far:
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <string.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
int fd[2];
pid_t sort_pid;
/* Create the pipe */
if(pipe(fd) == -1) {
fprintf(stderr, "Pipe failed\n");
exit(EXIT_FAILURE);
}
/* create child process that will sort */
sort_pid = fork();
if(sort_pid < 0) { // failed to fork
fprintf(stderr, "Child Fork failed\n");
exit(EXIT_FAILURE);
}
else if(sort_pid == 0) { // child process
close(0); // close stdin
dup2(fd[0], 0); // make stdin same as fd[0]
close(fd[1]); // don't need this end of the pipe
execlp("D:/Cygwin/bin/sort", "sort", NULL);
}
else { // parent process
close(1); // close stdout
dup2(fd[1], 1); // make stdout same as fd[1]
close(fd[0]); // don't need this end of the pipe
printf("Hello\n");
printf("Bye\n");
printf("Hi\n");
printf("G'day\n");
printf("It Works!\n");
wait(NULL);
}
return EXIT_SUCCESS;
}
This doesn't work, as it seems to go into an endless loop or something. I tried combinations of the wait() but that doesnt help either.
I am doing this to learn how to apply this idea in my actual program. In my actual program I read files, parse them line by line and save the processed data to a static array of structs. I want to be able to then generate output based on these results and use the fork() and execv() syscalls to sort the output.
This is ultimately for a project in uni.
These are similar examples which I dissected to get to the stage I am at so far:
- pipe() and fork() in c
- How to call UNIX sort command on data in pipe
- Using dup,pipe,fifo to communicate with the child process
Furthermore I read the manual pages on the relevant syscalls to try and understand them. I will admit my knowledge of pipes and using them is still basically nothing, as this is my first every try with them.
Any help is appreciated, even further sources of information I could look into myself. I seem to have exhausted most of the useful stuff a google search give me.
