【c++】动态绑定

C++的函数调用默认不使用动态绑定。要触发动态绑定，必须满足两个条件：

只有指定为虚函数的成员函数才能进行动态绑定
必须通过基类类型的引用或指针进行函数调用

因为每个派生类对象中都拥有基类部分，所以可以使用基类类型的指针或引用来引用派生类对象

示例

#include <iostream>

#include <string>

using namespace std;

struct base

{

    base(string str = "Base") : basename(str) {}

    virtual void print() { cout << basename << endl; }

    private:

        string basename;

};

struct derived : public base

{

    derived(string str = "Derived") : derivedname(str) {}

    void print() { cout << derivedname << endl; }

    private:

        string  derivedname;

};

int main()

{

    base b;

    derived d;

    cout << "b.print(), d.print()" << endl;

    b.print();

    d.print();

    base *pb = &b;

    base *pd = &d;

    cout << "pb->print(), pd->print()" << endl;

    pb->print();

    pd->print();

    base &yb = b;

    base &yd = d;

    cout << "yb.print(), yd.print()" << endl;

    yb.print();

    yd.print();

}

结果

分析

可以看出基类类型的指针或引用来引用派生类对象时，调用的是重定义的虚函数。要想覆盖虚函数机制，调用基函数的版本，可以使用强制措施。例：

代码

#include <iostream>

#include <string>

using namespace std;

struct base

{

    base(string str = "Base") : basename(str) {}

    virtual void print() { cout << basename << endl; }

    private:

        string basename;

};

struct derived : public base

{

    derived(string str = "Derived") : derivedname(str) {}

    void print() { cout << derivedname << endl; }

    private:

        string  derivedname;

};

int main()

{

    base b;

    derived d;

    cout << "b.print(), d.print()" << endl;

    b.print();

    d.base::print();

    base *pb = &b;

    base *pd = &d;

    cout << "pb->print(), pd->print()" << endl;

    pb->print();

    pd->base::print();

    base &yb = b;

    base &yd = d;

    cout << "yb.print(), yd.print()" << endl;

    yb.print();

    yd.base::print();

}

结果

巴特西

【c++】动态绑定

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