Thread: Shared Memory...

Hello people,

I am writing a program in C that is supposed to read from a shared memory segment and print the data on the screen. The shared memory segment is organized as an array of 23 objects, where an object is a complex datatype defined in a separate .h file.

Now, a couple things am not sure of...the SIZE parameter of shmget is based on what? I know it's the size of the mem segment in bytes, but in my program, how can I figure that out?

Here's my code:
****************************************

Code:

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

int main()
{
        int  shmid;
        int  m_key;
        char *data;
        int  size;

        m_key = 123456789;
        size  = 23*sizeof(int);
        shmid = shmget(m_key, size, 0444);
        data  = shmat(shmid, NULL, SHM_RDONLY);
        printf("Segment contains: \n%s\n", data);
        if (shmdt(data) == -1)
        {
                perror("shmdt");
                exit(1);
        }
        return 0;
}

****************************************
This code compiles, yet it only outputs a string out and exits. I initially had data[0],data[1], etc to be outputted...yet, that resulted in a segmentation fault!

Please, I'd appreciate any comment on how to go about this. I read several documents on shared memory, and it's not supposed to be hard at all, but I guess I am having a hard time implementing that.

Thank you!