Why Doesn't the Visual Studio 2010 Debugger See static const Class Members?

Question

This question is closely related to a subsequently asked question here.

The method of defining in-class constants is described here by Stroustrup.

When I follow Stroustrup's method I see the expected results. However, in Visual Studio 2010, the debugger cannot resolve a static const class member within that class's scope. Here is what I mean:

#include <iostream>

class Foo {
   public:
    static const int A = 50;
    char arr[A];
    void showA();
};

void Foo::showA() {
    std::cout << "showA = " << A << "\n";
}

int main() {
    Foo f;
    f.showA();
}

When the debugger is in showA() the "watch" window reports:

Error: Symbol "Foo::A" not found

I'd like to emphasize that the program does behave as expected i.e. the output is:

showA = 50

and the program returns 0.

Can anyone else reproduce this with Visual Studio 2010? Is this a bug in the debugger?

Answer 1

You could add a definition for your static data member at global namespace scope:

const int Foo::A;

Adding the static data member definition, which is not necessary but allowed, seems to solve your problem.

I tested this on a debug build with VS2010, and the value of A is correctly displayed in the debug window when the definition is present (while an error message is reported when the definition is missing, consistently with what you mention).

Answer 2

This isn't a bug. The compiler can (and almost always will) optimize out static constant basic types. Instead of allocating storage for A, the compiler is just inlining the value of A into the compiled instructions.

Because A isn't stored anywhere, it has no address, so the debugger cannot view it.