sem+pipe

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>

#include <string.h>
#include <sys/stat.h>
#include <sys/ipc.h>
#include <sys/sem.h>

#define N 5
#define LMES 15

int main() {
    char pathname[] = "c1.c";
    char msg[15] = "Hello, friend!";
    char resstring[15];

    int fd[2];
    int semid;

    key_t key;
    int resfork;
    int i = 0;
    ssize_t size;

    if ((key = ftok(pathname, 0)) < 0) { printf("e1\n"); exit(-1); }

    (void)umask(0000);
    if ((semid = semget(key, 1, 0666|IPC_CREAT)) < 0) { printf("e2\n"); exit(-1); }
    if (pipe(fd) < 0) { printf("e3\n"); exit(-1); }

    struct sembuf sembuf1;
    sembuf1.sem_flg = 0;
    sembuf1.sem_num = 0;

    resfork = fork();

    if (resfork < 0) {
        printf("e4\n");
        exit(-1);
    }

    else if (resfork == 0) {
        while (i < N) {
            if (write(fd[1], msg, LMES) != LMES) { printf("e5\n"); exit(-1); }
            sembuf1.sem_op = -1;
            if (semop(semid, &sembuf1, 1) < 0) { printf("e6\n"); exit(-1); }
            if ((read(fd[0], resstring, LMES) != LMES) || (strcmp(resstring, msg) != 0))
            { printf("e7\n"); exit(-1); }
            if (semop(semid, &sembuf1, 1) < 0) { printf("e8\n"); exit(-1); }
            ++i;
        }
        if (close(fd[0]) < 0) { printf("c1\n"); exit(-1); }
        if (close(fd[1]) < 0) { printf("c2\n"); exit(-1); }
    }

    else if (resfork > 0) {
        while (i < N) {
            if ((read(fd[0], resstring, LMES) != LMES) || (strcmp(resstring, msg) != 0))
            { printf("e9\n"); exit(-1); }
            if (write(fd[1], msg, LMES) != LMES) { printf("e10\n"); exit(-1); }
            sembuf1.sem_op = 2;
            if (semop(semid, &sembuf1, 1) < 0) { printf("e11\n"); exit(-1); }
            sembuf1.sem_op = 0;
            if (semop(semid, &sembuf1, 1) < 0) { printf("e12\n"); exit(-1); }
            ++i;
        }
        if (close(fd[0]) < 0) { printf("c3\n"); exit(-1); }
        if (close(fd[1]) < 0) { printf("c4\n"); exit(-1); }
    }

    return 0;
}