Accessing static fields by using decltype [duplicate]

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Closed 7 years ago.

Possible Duplicate:
C++0x decltype and the scope resolution operator

Compiling next example using g++ 4.6.1:

#include <iostream>

struct A
{
    static const int v = 1;
};

int main()
{
    A a;
    std::cout << decltype(a)::v << std::endl;
}

will produce next compiling errors:

error: expected primary-expression before 'decltype'
error: expected ';' before 'decltype'

Is this according to the standard? Or, is it a g++'s quirk?

Answer 1

It looks as if the compiler isn't recognizing the decltype keyword.

G++ 4.6.1 is new enough to include the decltype keyword. Did you enable C++11 mode with -std=gnu++0x or -std=c++0x?

The C++ grammar does permit a decltype-specifier to appear before :: in a qualified-id, so the code will be accepted by a conforming compiler. The error message is wrong, decltype(a)::v is a valid qualified-id, which is a primary-expression.

As a workaround, you can use a typedef. Example: http://ideone.com/clone/7FKUJ

Answer 2

It is Standard, or at least, it certainly was. I believe that there was a DR filed about this, and it might have been fixed in the final Standard but it might be due for a fix in the next Standard. It is as simple as that a decltype is not a valid grammatical production before ::.