c++ - how to set pointer to a memory to NULL using memset?

Question

I have a structure

typedef struct my_s {

   int x;
   ...
} my_T;

my_t * p_my_t;

I want to set the address of p_my_t to NULL and so far this is how I've tried to do this:

memset (&p_my_t, 0, sizeof(my_t*))

This doesn't not look right to me though. What is the correct way of doing this?

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Amendment to question - asking a radically more complex question:

Here is what I am trying to do:

• Two processes, A and B
• malloc p_my_t in A, B has N threads and can access it
• Start deleting in A but I can not simply free it since threads in B may still using it.
• So I call a function, pass address of p_my_t to B to set its address to NULL in B so no other threads in B can use anymore
• After call back from B, I then free memory in A

NB: there is no standard way to manage memory allocations via shared memory between processes. You will have to do some rather careful thinking about what is going on.

Answer 1

Don't use memset to initialize a null pointer as this will set the memory to all bits zero which is not guaranteed to be the representation of a null pointer, just do this:

p_my_t = NULL;

or the equivalent:

p_my_t = 0;