typedef and using in c++11

Question

#include <iostream>

struct cls {
    using type = double;          //case 1
    // typedef double type;         //case 2
};

template<typename T>
void foo(typename T::type) {
    std::cout<<"T::type\n";
}

int main() {
    foo<cls>(22.2);
}

I believe using and be used instead of typedef. In the above code I'm getting error for case 1 but not for case 2.

error: expected nested-name-specifier before 'type'

Could someone please explain why??

I can't reproduce: http://ideone.com/4gD45z What compiler version and flags do you use? — stefan, Apr 20 '15 at 06:49

score 2 · Accepted Answer · edited May 23 '17 at 10:10

Your compiler either doesn't support C++11 type aliases, has limited support for them (MSVC used to incorrectly parse template types when not used) or hasn't the C++11 option active, make sure you're using a C++11 compatible (and enabled) one, i.e. upgrade your compiler.

struct cls {
    using type = double;         // Doesn't work on pre-C++11
    // typedef double type;      // Works on pre-C++11
};

I'm also recommending reading the difference between using and typedef in C++11

typedef and using in c++11

1 Answers1