Shared memory example

shm.c

#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>
#include <sys/shm.h>
#include <stdio.h>
#include <string.h>

int main(void)
{
    /* shared memory segment */
    int shmid = shmget(IPC_PRIVATE, sizeof(int), IPC_CREAT | 0666);
    if (shmid == -1) {
        perror("shmget");
        return EXIT_FAILURE;
    }
    int *state = shmat(shmid, NULL, 0);
    if (*state == -1) {
        perror("shmat");
        return EXIT_FAILURE;
    }

    *state = 0;

    pid_t pid = fork();
    if (pid == 0) {
        int *temp = shmat(shmid, NULL, 0);
        *temp = 42;
        shmdt(temp);
    } else {
        int stat_loc = 0;
        waitpid(pid, &stat_loc, 0);
        char *sig_str = strsignal(WTERMSIG(stat_loc));
        printf("{\"state\": %d, \"stat_loc\": %d, \"signal\": \"%s\"}\n", *state, stat_loc, sig_str);
        free(sig_str);
        if (shmdt(state) == -1) {
            perror("shmdt");
            return EXIT_FAILURE;
        }
        if (shmctl(shmid, IPC_RMID, NULL) == -1) {
            perror("shmctl");
            return EXIT_FAILURE;
        }
    }

    return EXIT_SUCCESS;
}