Compiler Warning (level 3) C4686

'user-defined type' : possible change in behavior, change in UDT return calling convention

Remarks

A class template specialization wasn't defined before it was used in a return type. Anything that instantiates the class resolves C4686; declaring an instance or accessing a member (for example, C<int>::some_member) are also options.

This warning is off by default. For more information, see Compiler warnings that are off by default.

Example

Try the following instead:

// C4686.cpp
// compile with: /W3
#pragma warning (default : 4686)
template <class T>
class C;

template <class T>
C<T> f(T);

template <class T>
class C {};

int main() {
   f(1);   // C4686
}

template <class T>
C<T> f(T) {
   return C<int>();
}