Using pipes to communicate between a parent and a child - c

Question

In an attempt to better understand how pipes work in C, I decided to create a simple program. It is supposed to do the following: Firstly, I fork the program. The parent then reads from the standard input and writes everything into a pipe until EOF is reached. The child then reads from that pipe and writes the content back into another pipe, which is then supposed to be read by the parent process and written into the standard output.
Yes, the program isn't very "useful", but I'm just trying to familiarize myself with pipes and how to use them. This is my code:
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/wait.h>
int main(int argc, char **argv) {
char buf;
int pipe_one[2];
int pipe_two[2];
pid_t child;
if(pipe(pipe_one) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
if(pipe(pipe_two) == -1) {
perror("pipe");
exit(EXIT_FAILURE);
}
child = fork();
switch (child) {
case -1:
fprintf(stderr, "Error while forking.\n");
break;
case 0:
// child
// close unnecessary ends
close(pipe_one[1]);
close(pipe_two[0]);
// read input from parent and write it into pipe
while(read(pipe_one[0], &buf, 1) > 0) {
write(pipe_two[1], &buf, 1);
}
write(pipe_two[1], "\n", 1);
close(pipe_one[0]);
close(pipe_two[1]);
break;
default:
// parent
// close unnecessary ends
close(pipe_one[0]);
close(pipe_two[1]);
// read from standard input and write it into pipe
while(read(STDIN_FILENO, &buf, 1) > 0) {
write(pipe_one[1], &buf, 1);
}
write(pipe_one[1], "\n", 1);
close(pipe_one[1]);
// wait for child process to finish
wait(NULL);
// read from pipe that child wrote into
while(read(pipe_two[0], &buf, 1) > 0) {
write(STDOUT_FILENO, &buf, 1);
}
write(STDOUT_FILENO, "\n", 1);
close(pipe_two[0]);
break;
}
exit(EXIT_SUCCESS);
}
Expected behavior: In the beginning, the program reads user input until EOF is reached and then it outputs everything again into the standard output.
Actual behavior: The program reads the whole input, but once EOF is reached it just terminates (succesfully) without writing anything into the standard output. What am I doing wrong? I'd be happy if someone could look over it and help me out.

Answer 1

You close pipes for your parent in your child.
while(read(pipe_one[0], &buf, 1) > 0) {
write(pipe_two[1], &buf, 1);
}
write(pipe_two[1], "\n", 1);
close(pipe_one[0]); // Here you close pipes
close(pipe_two[1]); // for your parent
So the parent can't receive anything. Just remove those two lines and it will work.