Compiler Warning (level 3) C4686

 

For the latest documentation on Visual Studio 2017 RC, see Visual Studio 2017 RC Documentation.

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

A class template specialization was not is defined before it was used in a return type. Anything that instantiates the class will resolve C4686; declaring an instance or accessing a member (C<int>::anything) are also options.

This warning is the result of work to make the Visual C++ .NET 2003 compiler conform to the ISO C++ standard.

This warning is off by default. See Compiler Warnings That Are Off by Default for more information.

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>();  
}  

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