Problem with shared memory

I'm trying to use shared memory. So far I have

Code:

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#include <sys/ipc.h>
#include <sys/shm.h>
#include <sys/types.h>
#include <unistd.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_PATH_LEN 1024
#define ARRAY_SIZE 50

typedef struct _task{
        char path [MAX_PATH_LEN];
        char thread_id[MAX_PATH_LEN];
        char op;
        int index;
}task;

typedef struct _sharedMem{
        int lastIn;
        int numTasks;
        sem_t mutex;
        int size;
        task array [ARRAY_SIZE];
}sharedMem;

int main(void){
        int i;
        int id = shmget(1234, sizeof(sharedMem), IPC_CREAT|0777);
        sharedMem* shMem = shmat(id, NULL, 0);
        printf("init 1\n");
        shMem->lastIn = 0;
        printf("init 2\n");
        shMem->numTasks = 0;
        printf("init 3\n");
        sem_init(&(shMem->mutex), 0, 1);
        printf("init 4\n");
        shMem->size = ARRAY_SIZE;
        for(i = 0; i < shMem->size; i++){
                strcpy(shMem->array[i].path, " ");
        }
        return 1;
}

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The output for this is

Code:

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init 1
Segmentation fault

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I have no idea why. Do we have to do something to the structure before start using it?
If so what?

You should check all the system calls status, are you sure your shm object is correctly created and attached? no.

PS: you should use ftok() to create a key_t typed object instead of '1234', because some values are reserved

For reference:
ftok() gets you a key_t value - to then pass to semget() for a valid shmid - which can then be passed to shmat().

The other Posix API for shared memory is shm_open(), mmap(), and shm_unlink().

Do yourself a big favor and get into the habit of always checking return values and error codes.

gg