请支持原创~~
1. 功能
用在类中成员函数声明的地方,用以标记一个virtual function 是重写另一个 virtual function;
2. 语法
- 只声明时,override 紧跟参数的右括号,如果是纯虚函数,override 会出现在 = 0 之前;
- 类中定义时,override 在 函数体之前;
3. 举例
#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';
}
重写的函数加上override,那么该成员函数需要满足:
- 成员函数为 虚函数;
- 成员函数从父类继承,在子类重写;
另外,如同 关键字 final, 只是一个标识,在使用成员函数时有特殊的意义。而在其他情况下可以作为一个对象名、函数名、类名使用。
结果:
B::foo();
B::override();
override: 42
B::~B();
A::~A();
4. 原文摘录
Specifies that a virtual function overrides another virtual function.
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.
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.
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.