how memory allocation is done

Question

I am expecting NULL pointer exception but I am getting output 222. How is this working.

int main()
{
    int *p = (int*)malloc(0);
    *p = 222;
    cout << *p;
    return 0;
}

It's implementation-defined if [`malloc`](http://en.cppreference.com/w/c/memory/malloc) returns a null pointer or not when allocating zero bytes. Just don't do it. — Some programmer dude, Sep 21 '18 at 10:57
@Downvoter: this is an "edge case" in the language standards. — Bathsheba, Sep 21 '18 at 11:00

score 2 · Accepted Answer · answered Sep 21 '18 at 10:59

The behaviour of your program is undefined.

The behaviour of malloc with 0 passed is implementation defined: it can return 0 or a pointer. If it returns a pointer, then you must pass that pointer to free, but you must not deference that pointer.

C and C++ do not differ in this respect.

score 0 · Answer 2 · answered Sep 21 '18 at 11:01

I am expecting NULL pointer exception

Your expectation is misguided.

Firstly, malloc is not guaranteed to retrurn a null pointer when allocating 0 size.

Secondly, indirecting a null pointer (or any pointer returned by malloc(0)) is not guaranteed to cause an exception. Instead the behaviour is undefined.

how memory allocation is done

2 Answers2