C++ How do you set an array of pointers to null in an initialiser list like way?

In order to set an array of pointers to nulls in constructor initializer list, you can use the () initializer

struct S {
  int *a[100];

  S() : a() {
    // `a` contains null pointers 
  }
};

Unfortunately, in the current version of the language the () initializer is the only initializer that you can use with an array member in the constructor initializer list. But apparently this is what you need in your case.

The () has the same effect on arrays allocated with new[]

int **a = new int*[100]();
// `a[i]` contains null pointers 

In other contexts you can use the {} aggregate initializer to achieve the same effect

int *a[100] = {};
// `a` contains null pointers 

Note that there’s absolutely no need to squeeze a 0 or a NULL between the {}. The empty pair of {} will do just fine.