CODEWITHSUNDEEP
c++templates
Alok
Alok

Reputation: 127

Function return type for template class inside template class

I am using c++ templates and created a template class inside a template class.

the situation is like this:

template <typename T>
class C {
    public:
    class N {
        T v;
    };

    template <typename D>
    N *fun(D d);
};

template <typename T>
template <typename D>
N *C<T>::fun(D d) {
}

int main() {
    C<int> obj;
    obj.fun('c');
}

Now compiler is giving error as:

main.cpp:14:1: error: ‘N’ does not name a type

If I use the function prototype outside class as C<T>::N *C<T>::fun(D d), compiler gives error:

main.cpp:14:1: error: need ‘typename’ before ‘C::N’ because ‘C’ is a dependent scope

If I define definition inside the class then it works fine. But I don't want to make it inline, how should I do it?

Upvotes: 4

Views: 533

Answers (2)

eike
eike

Reputation: 1334

As the compile error suggests, use typename

template <typename T>
template <typename D>
typename C<T>::N *C<T>::fun(D d) {
}

Upvotes: 8

Jarod42
Jarod42

Reputation: 217265

As alternative, you might use trailing return type:

template <typename T>
template <typename D>
auto C<T>::fun(D d) -> N*
{
    return nullptr;
}

Upvotes: 2

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