How do I forward a declared template class in C++?

4 Answers. This is how you would do it: template class Mappings; template class Mappings { public: Type valueFor(const IDType& id) { // return value } };

Can you forward declare templates?

It’s simply wrong. std::string is not a class, but a typedef to std::basic_string . And no, you can’t simply add a forward declaration to template class basic_string; because that’s not all there is to it, either. Don’t be tempted to forward declare those classes and templates, either.

Can you forward declare an enum class?

You can forward-declare an enum in C++11, so long as you declare its storage type at the same time.

How do I forward a typedef declaration?

To “fwd declare a typedef” you need to fwd declare a class or a struct and then you can typedef declared type. Multiple identical typedefs are acceptable by compiler. Because to declare a type, its size needs to be known. You can forward declare a pointer to the type, or typedef a pointer to the type.

Can a template be a forward declaration in C + +?

And no, you can’t simply add a forward declaration to template class basic_string ; because that’s not all there is to it, either. There surely are things in other libraries that are easier to provide forward declarations for, right?

Which is an example of a forward declaration?

If, however, you happen to be on the other side and write libraries yourself, consider to provide headers that contain forwarding declarations for your classes and templates. An example is the standard header that provides forward declarations for things related to iostreams and the like.

How does class declaration work in cppreference.com?

Declares a class type which will be defined later in this scope. Until the definition appears, this class name has incomplete type. This allows classes that refer to each other: and if a particular source file only uses pointers and references to the class, this makes it possible to reduce #include dependencies:

What happens if forward declaration appears in local scope?

If forward declaration appears in local scope, it hides previously declared class, variable, function, and all other declarations of the same name that may appear in enclosing scopes: