c ++模板似乎打破了访问说明符

Question

The following code doesn't compile for obvious reasons, namely that Foo is trying to access a private member of Bar. However if you uncomment/comment the lines marked, making Foo a template, it does compile and outputs 42. What am I missing here? Why does this work? Seems to me it shouldn't.

Thanks for your help.

#include <iostream>

class Bar {
    private:
    static const int x = 42;
};

//template <int>   // uncomment me
struct Foo {
    static const int i = Bar::x;
};

int main(int argc, char* argv[]) {

    std::cout << Foo::i    << std::endl;   // comment me
    //std::cout << Foo<0>::i << std::endl;   // uncomment me
}

Answer 1

If you are seeing this behavior, it is a compiler bug.

Both Comeau Online and Visual C++ 2010 reject the code as invalid because Bar::x is inaccessible. g++ 4.1.2 incorrectly accepts the invalid code (someone would need to test with a later version to see if it's been fixed; that's the only version I have on this laptop).

Answer 2

This seems like GCC bug 40843 . It is listed as UNCONFIRMED, but I can reproduce it on g++ (Ubuntu 4.4.3-4ubuntu5) 4.4.3 as well.

Answer 3

VisualStudio 2010说“错误C2248：'Bar :: x'[...]由于平台没有规定，我已经评估了几乎在Windows VC9上的假设是假的。