Question

I’m trying to use is_member_pointer from the type_traits header, with the following syntax, for example:

cout << is_member_pointer<decltype(&vector<int>::member)>::value;

In the case of vectors, I get a “template argument invalid” and a wordy “type of … is unknown” message for all iterator functions and all modifier functions except for clear. There are similar faults for other container functions. I have mingw g++ 4.6.2.

Is there a way to help this?

Answer 1

The problem probably is that you checked the type of overloaded methods. That is not possible, since expressions like &std::vector<int>::begin have no type (there are two overloads). It is only after casting to the desired type, that it becomes a member function pointer. The cast would look like this:

std::cout << std::is_member_pointer<decltype((std::vector<int>::iterator(std::vector<int>::*)())&std::vector<int>::begin)>::value;

not very aesthetically pleasing.

With non-overloaded methods, it works.

std::cout << std::is_member_pointer<decltype(&std::vector<int>::reserve)>::value;

BTW with gcc-4.7, you even get a clearer error message:

test.cpp:6:70: error: decltype cannot resolve address of overloaded function