override specifier (since C++11)

 

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override specifier (C++11)

final specifier (C++11)

 

Specifies that a virtual function overrides another virtual function.

Syntax

The identifier override, if used, appears immediately after the declarator in the syntax of a member function declaration or a member function definition inside a class definition.

declarator virt-specifier-seq (optional) pure-specifier (optional)	(1)
declarator virt-specifier-seq (optional) function-body	(2)

1) In a member function declaration, override may appear in virt-specifier-seq immediately after the declarator, and before the pure-specifier, if used.

2) In a member function definition inside a class definition, override may appear in virt-specifier-seq immediately after the declarator and just before function-body.

In both cases, virt-specifier-seq, if used, is either override or final, or final override or override final.

Explanation

In a member function declaration or definition, override specifier ensures that the function is virtual and is overriding a virtual function from a base class. The program is ill-formed (a compile-time error is generated) if this is not true.

override is an identifier with a special meaning when used after member function declarators: it's not a reserved keyword otherwise.

Example

Run this code

#include <iostream>
 
struct A
{
    virtual void foo();
    void bar();
    virtual ~A();
};
 
// member functions definitions of struct A:
void A::foo() { std::cout << "A::foo();\n"; }
A::~A() { std::cout << "A::~A();\n"; }
 
struct B : A
{
//  void foo() const override; // Error: B::foo does not override A::foo
                               // (signature mismatch)
    void foo() override; // OK: B::foo overrides A::foo
//  void bar() override; // Error: A::bar is not virtual
    ~B() override; // OK: `override` can also be applied to virtual
                   // special member functions, e.g. destructors
    void override(); // OK, member function name, not a reserved keyword
};
 
// member functions definitions of struct B:
void B::foo() { std::cout << "B::foo();\n"; }
B::~B() { std::cout << "B::~B();\n"; }
void B::override() { std::cout << "B::override();\n"; }
 
int main()
{
    B b;
    b.foo();
    b.override(); // OK, invokes the member function `override()`
    int override{42}; // OK, defines an integer variable
    std::cout << "override: " << override << '\n';
}

Output:

B::foo();
B::override();
override: 42
B::~B();
A::~A();

See also

final specifier(C++11)

declares that a method cannot be overridden