Thread: Trying to add an array of Integers to a POSIX Shared memory Object

Greetings all, I am really new to C and have been using it for about 1 month now at most. I am attempting to store an array from a function into a shared memory object, but I am unsure of how do so.

I know how to do it with Strings, but not really with an array of integers. The code is supposed to generate a collatz sequence of integers and add it to the shared memory object for another process/program to access it. Here is the code:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <sys/mman.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>

int *calcCollatz(int n) {
    int solution;

    int *collatzSeq = malloc(sizeof(int));
    int j = 0;
    while (n != 1) {
        if (n % 2 == 0) {
            solution = n / 2;
            n = solution;
            collatzSeq[j] = n;
            j++;
            return collatzSeq;
        } else {
            solution = (3 * n) + 1;
            n = solution;
            collatzSeq[j] = n;
            j++;
            return collatzSeq;
        }
    }


}

int main(int argc, char *argv[])
{
    const int SIZE = 4096; //size in bytes of Shared Memory Object
    const char *sharedObj = "Shm"; //name of the Shared memory Object
    int shm_fd; //Shared memory file descriptor
    void *ptrShm; //Pointer to shared memory object
    shm_fd = shm_open(sharedObj, O_CREAT | O_RDWR, 0666); //Create Shared Memory Object
    ftruncate(shm_fd, SIZE); //configure the size of the shared memory object
    ptrShm = mmap(0, SIZE, PROT_WRITE, MAP_SHARED, shm_fd, 0); //Map the shared memory object in the space of the process

    if (ptrShm == MAP_FAILED) {
        printf("Map Failed\n");
        return -1;
    }

    sprintf(ptrShm, argv[1]);
    ptrShm += strlen(argv[1]);

    sprintf(ptrShm, calcCollatz(atoi(argv[1])));
    ptrShm += sizeof(calcCollatz(atoi(argv[1])));


    printf("Writing the sequence to a shared memory object!\n");
    return 0;
}

The int * collatz sequence method generates a sequence of integers per a collatz sequence until the value reaches 1. Please let me know if you need a clearer explanation.