New to IPC, can't get my pipe to work - c

Question

Sorry for the length of this post... I've encountered about a zillion problems in this. Up front I'll say I'm a student and my professor is a worthless resource. So, all I want to to do is have producer fork, then the parent producer will count some stuff in a file and send two ints to consumer, which was launched by the child process. I've tested everything, the fork and the file stuff works and I have printf statements all over the place so I know what is being done and where the code is at.
When I added the
if (pipe(pipefd) == -1) {
perror("pipe");
}
it caused my parent to just terminate. It reaches "parent pipe open" but then it dies. I checked with $ ps to see if it was just hung, but it's not there; it just dies. If I take that snippet out, it runs to the end but I presume if that code isn't there, then it's not actually aware that pipefd is a pipe... right?
I did search on this site and found another example of this and followed what he did as well as the answer and mine just refuses to work. I'm pretty sure it's a trivially easy thing to fix but I've run out of ideas of what to try :(
I don't really want to post all my code because it'll be a huge wall of text but I don't want to accidentally cut something out that turns out to be important either.
producer.c
#include <stdio.h> /* printf, stderr, fprintf */
#include <sys/types.h> /* pid_t */
#include <unistd.h> /* _exit, fork, execl */
#include <stdlib.h> /* exit */
#include <errno.h> /* errno */
#include <string.h> /* strlen */
#include <sys/wait.h> /* wait */
#define SLEEP_TIME 8
int main (int argc, char *argv[]){
//PID
pid_t local_pid;
local_pid = fork();
//Logic to determine if the process running is the parent or the child
if (local_pid == -1) {
/* Error:
* When fork() returns -1, an error happened
* (for example, number of processes reached the limit).
*/
fprintf(stderr, "can't fork, error %d\n", errno);
exit(EXIT_FAILURE);
} else if (local_pid == 0) {
//Child specific code
int child;
char *temp[] = {NULL};
printf("Child PID found\n");
child = execv("./consumer", temp);
_exit(0);
} else {
//Parent specific code
printf("Parent running\n");
//open file
FILE * randStrings;
randStrings = fopen("randStrings.txt", "r");
int file_length;
int num_of_e = 0;
int c; //using this as a char
//until eof
while (feof(randStrings) == 0) {
c = fgetc(randStrings);
//calculate length of file
file_length++;
//count e chars
if (c == 'e') {
num_of_e++;
}
}
//close file
fclose(randStrings);
//send bundle to child
int a[2];
a[0] = num_of_e;
a[1] = file_length;
printf("num of e = %i\n", a[0]);
printf("len = %i\n", a[1]);
//set up parent pipe
int pipefd[2];
if (pipe(pipefd) == -1) {
perror("pipe");
printf("x\n");
}
printf("parent pipe open\n");
close(pipefd[0]); //close the read end
write(pipefd[1], &a[0], sizeof(int));
write(pipefd[1], &a[1], sizeof(int));
close(pipefd[1]);
printf("parent pipe closed\n");
//wait for child to finish running
wait(NULL);
printf("parent out\n");
//terminate
}
}
and consumer.c
#include <stdio.h> /* printf, stderr, fprintf */
#include <sys/types.h> /* pid_t */
#include <unistd.h> /* _exit, fork, execl */
#include <stdlib.h> /* exit */
#include <errno.h> /* errno */
#define SLEEP_TIME 5
int main (int argc, char *argv[]){
sleep(SLEEP_TIME);
printf("Child program launched\n");
//receive bundle
int pipefd[2];
int buf[2];
if (pipe(pipefd) == -1) {
perror("pipe");
printf("child x\n");
}
close(pipefd[1]); //child closes write end
buf[0] = 0;
buf[1] = 0;
/*int i = 0; // i dont like this
while (read(pipefd[0], &buf[i], sizeof(int)) > 0) {
i++;
}*/
printf("child reading pipe\n");
read(pipefd[0], &buf[0], sizeof(int));
read(pipefd[0], &buf[1], sizeof(int));
close(pipefd[0]);
//buf should have the stuff in it
int num_of_e = buf[0];
int file_length = buf[1];
printf("child num of e = %i\n", num_of_e);
printf("child len = %i\n", file_length);
//open file
FILE * resultStrings;
resultStrings = fopen("resultStrings.txt", "w");
for (int i = 0; i < num_of_e; i++) {
//write num_of_e e chars
fputc('e', resultStrings);
}
//or if no e chars, write - chars
if (num_of_e == 0) {
for (int i = 0; i < file_length; i++) {
//write file_length '-' chars
fputc('-', resultStrings);
}
}
//close file
fclose(resultStrings);
printf("child out\n");
}
if you're still here after all that, you deserve a thank you just due to the length of this.

Answer 1

You're doing it wrong. The whole mechanism works because a child process inherits the parent's open file descriptors.
It should go like this:
Open the pipe with pipe(pipefd)
fork()
Parent (producer):
closes the read side (pipefd[0])
writes to the write side (pipefd[1])
Child (consumer):
closes the write side (pipefd[1])
reads from the read side (pipefd[0]) or calls exec
You are opening distinct pipes in both the parent and child process (after you've forked.) It needs to happen before you fork.
Now since you're execing, the new process needs to be aware of read-only pipe. There are a couple ways you could do this:
Pass it the file descriptor number (pipefd[0]) on the command line
dup2(1, fd) it to be the stdin of the newly exec'd process