Accessing a variable using namespace and a template class

Question

I can't access the variable width .

The Ah file:

namespace AN{
    template <typename T> class A{
    public:
        unsigned int width; #The variable
        ...
    }
}

The B.cpp file:

#include "A.h"
using namespace AN;
namespace BN{
    bool something(){
        unsigned int * w = AN::&width;
    }
}

I tried also AN::A::&width but it doesn't work as well.

Answer 1

This has nothing to do with templates. It's about classes and objects. The address of width is determined by the object that it's a part of; without an object, there is no width.

However, without an object you can create a pointer-to-member; it's not an ordinary pointer (if it was, it would be called "pointer"). Like this:

class A {
public:
    int width;
};

int A::*w = &A::width;

You use it to access that variable when you create an object:

A a;
a.*w = 3;
A aa;
aa.*w = 4;

If you really only want one value of width for every object of your type, yes, you can make it a static member:

class A {
public:
    static int width;
};
int A::width;

Now you can create a pointer to that member as an ordinary pointer:

int* w = &A::width;

and you can use w as an ordinary pointer:

*w = 3;