Question

If I have a

class A
{
private:
  Widget* widgets[5];
};

Is it guaranteed that all pointers are NULL, or do I need to initialize them in the constructor? Is it true for all compilers?

Thanks.

Answer 1

It depends on the platform and how you allocate or declare instances of A. If it’s on the stack or heap, you need to explicitly initialize it. If it’s with placement new and a custom allocator that initializes memory to zero or you declare an instance at file scope AND the platform has the null pointer constant be bitwise zero, you don’t. Otherwise, you should.

EDIT: I suppose I should have stated the obvious which was “don’t assume that this happens”.

Although in reality the answer is “it depends on the platform”. The standard only tells you what happens when you initialize explicitly or at file scope. Otherwise, it is easiest to assume that you are in an environment that will do the exact opposite of what you want it to do.

And if you really need to know (for educational or optimizational purposes), consult the documentation and figure out what you can rely on for that platform.