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:
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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; }

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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!