• 重载：overload
• 重写：override
• 重定义：redefine

final

Specifies that a virtual function cannot be overridden in a derived class or that a class cannot be derived from.

#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';
}

override

Specifies that a virtual function overrides another virtual function.

#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';
}