C :: How To Apply Mutex Lock On Shared Memory

I was trying to put mutex lock on shared memory but my code is not working. What I want is that if some process is putting something on shared memory segment, other process should not be able to access that segment. For testing , I create a server program which put data in shared memory and client program which access the data.

To test it, I put break point after:

pthread_mutex_lock(&(init_lock));

But I see that client program was able to access shared memory.

Below is code:

Server: Code: pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
main()
{
char c;

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