Can I forward declare an enum?

There is indeed no such thing as a forward declaration of enum. As an enum’s definition doesn’t contain any code that could depend on other code using the enum, it’s usually not a problem to define the enum completely when you’re first declaring it.

What are forward declarations in C?

A forward declaration tells the compiler about the existence of an entity before actually defining the entity. Forward declarations can also be used with other entity in C++, such as functions, variables and user-defined types.

What is typedef enum in CPP?

The typedef keyword allows us to rename a data type to a name that has more meaning to our program. The typedef statement may be specified by itself or as part of a enum or struct definition. The typedef defined new name is often the given the same name as the enum or struct definition.

What is function forward declaration?

A forward declaration allows us to tell the compiler about the existence of an identifier before actually defining the identifier. In the case of functions, this allows us to tell the compiler about the existence of a function before we define the function’s body.

How do I forward a declared nested class?

You cannot forward declare a nested structure outside the container. You can only forward declare it within the container. Create a common base class that can be both used in the function and implemented by the nested class.

Is a forward declaration Objective C?

In Objective-C, classes and protocols can be forward-declared if you only need to use them as part of an object pointer type, e.g. MyClass * or id. Forward declaration of a class or protocol is not sufficient if you need to subclass that class or implement that protocol.

Is forward declaration good?

Use forward declarations (as in your example) whenever possible. This reduces compile times, but more importantly minimizes header and library dependencies for code that doesn’t need to know and doesn’t care for implementation details.

Does C have enum?

Enumeration (or enum) is a user defined data type in C. It is mainly used to assign names to integral constants, the names make a program easy to read and maintain. The keyword ‘enum’ is used to declare new enumeration types in C and C++. …

Are C enums ints?

Yes. In C enum types are just int s under the covers. Typecast them to whatever you want.

When can you use forward declaration?

This is especially useful inside class definitions, e.g. if a class contains a member that is a pointer (or a reference) to another class. Forward-declaration is used to avoid unnecessary coupling which help reducing compilation time by reducing the number of header inclusion.

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 inner class have constructor?

5 Answers. You can observe the constructor chain for the inner class when you extend an inner class. so you can see that you are able to call the super constructor of your nested class passing to that constructor the MainClass , and calling . super on mainClass object instance.

How to forward declaration of a struct in C?

A struct (without a typedef) often needs to (or should) be with the keyword struct when used. struct A; // forward declaration void function ( struct A *a ); // using the ‘incomplete’ type only as pointer. If you typedef your struct you can leave out the struct keyword.

When to use a forward declaration in a typedef?

You never need to use a forward declaration that something else actually requires (unless it’s a typedef), because it has a forward declaration part of its own line. Being able to use an incomplete type allows the type to be completed later on, before it is used.

How to forward declare a function in C + +?

You can easily create forward declarations by using copy/paste on your function declaration. Don’t forget the semicolon on the end. New programmers often wonder what happens if they forward declare a function but do not define it. The answer is: it depends.

Why are forward declarations of a class called forward?

See (the end of) this answer for why a “forward declaration” of a class really is just a simple class declaration with a fancy name. In other words, the “forward” just adds ballast to the term, as any declaration can be seen as being forward in so far as it declares some identifier before it is used.