Question

I am trying to write a file with data into my shared memory segment. However everything I have tried seems just to give the error Segmentation fault. I have been searching the internet for help for more then one day.

int main(int argc, char *argv[]).
{
    int sm;
    char *data;
    int pid=atoi(argv[1]);
    int key=atoi(argv[2]);
    char (*d)[1025];
    data=(char*) malloc(1025);


    //put the data in the shared memory segment
    FILE *file=fopen(argv[3], "r"); //r for read
    if (file==0)
    {printf("Could not open file");}
    else
    {
        while(fgets(data, 1025, file)!=NULL)
        {
            fputs(data, file);
        //  puts(d);
        }       
        fclose(file);
    }

    //access shared memory 
    //S_IWUSR gives owner the write permession
    sm = shmget(key, 1024, S_IWUSR); 
    //create a pointer to the shared memory segment
    d =  shmat(sm, (void *)0, 0); //shared memory id, shmaddr, shmflg
    //for (int j=0; j<100; j++)
        strcpy(d[0], data);

    shmdt(d); //detach the shared memory segment
    //remove the shared memory segment
    shmctl(sm, IPC_RMID, NULL);
}

Any help would be greatly appreciated
Thanks in advance

EDIT: added malloc

EDIT2: maybe I should rephrase my question, my problem is to get the data into my shared memory

Answer 1

+1 about rjayavrp answer

And I can add that data is not allocated… This is just a pointer and not a array of chars..

Moreover what are you trying to do with

char (*d)[1025];

A quick and dirty example :

#include <stdio.h>
#include <stdlib.h>
#include <sys/ipc.h>
#include <sys/shm.h>

#define SIZE_SHARED_MEMORY  1024

int main(int argc, char *argv[])
{
    int sm = -1;
    char *d = NULL;
    FILE *file = NULL;
    key_t key = 0;
    int ret = 0;

    if (argc != 4)
    {
        return 1;
    }

    key = atoi(argv[2]);

    //access shared memory
    sm = shmget(key, SIZE_SHARED_MEMORY, IPC_CREAT | 0600);
    if (sm == -1)
    {
        perror("shmget : Failed");
        return 2;
    }

    //create a pointer to the shared memory segment
    d =  shmat(sm, (char *)0, 0);
    if (d == (void *)-1)
    {
        perror("shmat : Failed");
        return 3;
    }

    // Open the file
    file = fopen(argv[3], "r");
    if (file == NULL)
    {
        perror("fopen : Failed");
        ret  = 4;
    }
    else
    {
        if(fgets(d, SIZE_SHARED_MEMORY, file) == NULL)
        {
            perror("fgets : Failed");
            ret = 5;
        }
        fclose(file);
    }

    shmdt(d); //detach the shared memory segment

    // remove the shared memory segment ???
    // Don't understand why you are doing this
    shmctl(sm, IPC_RMID, NULL);

   return ret;
}