Function return type specifiers

The result of a function is called its return value and the data type of the return value is called the return type.

Every function declaration and definition must specify a return type, whether or not it actually returns a value.

If a function declaration does not specify a return type, the compiler assumes an implicit return type of int. However, for conformance to C99, you should specify a return type for every function declaration and definition, whether or not the function returns int.

A function may be defined to return any type of value, except an array type or a function type; these exclusions must be handled by returning a pointer to the array or function. When a function does not return a value, void is the type specifier in the function declaration and definition.

A function cannot be declared as returning a data object having a volatile or const type, but it can return a pointer to a volatile or const object.

enum count {one, two, three};
enum count counter();

The user-defined type may also be defined within the function declaration. The user-defined type may not be defined within the function declaration.

enum count{one, two, three} counter();   // legal in C
enum count{one, two, three} counter();   // error in C++

References can also be used as return types for functions. The reference returns the lvalue of the object to which it refers.