C++ Constructor initialization list strangeness

Question

I have always been a good boy when writing my classes, prefixing all member variables with m_:

class Test {
    int m_int1;
    int m_int2;
public:
    Test(int int1, int int2) : m_int1(int1), m_int2(int2) {}
};

int main() {
    Test t(10, 20); // Just an example
}

However, recently I forgot to do that and ended up writing:

class Test {
    int int1;
    int int2;
public:
    // Very questionable, but of course I meant to assign ::int1 to this->int1!
    Test(int int1, int int2) : int1(int1), int2(int2) {}
};

Believe it or not, the code compiled with no errors/warnings and the assignments took place correctly! It was only when doing the final check before checking in my code when I realised what I had done.

My question is: why did my code compile? Is something like that allowed in the C++ standard, or is it simply a case of the compiler being clever? In case you were wondering, I was using Visual Studio 2008

Answer 1

Yes, it's valid. The names in the member initializer list are looked up in the context of the constructor's class so int1 finds the name of member variable.

The initializer expression is looked up in the context of the constructor itself so int1 finds the parameter which masks the member variables.