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//二义性
#include <iostream>
using namespace std;
class Base{
public:
Base(){
cout << "Base called..." << endl;
}
void print() {
cout << "Base ::print()" << endl;
}
};
class Sub{
public:
Sub(){
cout << "Sub called..." << endl;
}
void print(){
cout << "Sub print...." << endl;
}
};
class Child: public Base, public Sub{
public:
Child(){
cout << "Child called..." << endl;
}
};
int main(void){
Child c;
//c.print();报错,这里c类中的有两个print()函数,它们的地位相同
c.Base::print();
c.Sub::print();
return 0;
}//砖石继承,二义性
#include <iostream>
using namespace std;
int gFlag = 0;
class Base{
public:
Base(){
cout << "Base::Base()" <<++gFlag << endl;
}
void print(){
cout << "Base::print()" << endl;
}
};
class Mid1:public Base{
public:
Mid1(){
cout << "Mid1:Mid1()" << endl;
}
};
class Mid2:public Base{
public:
Mid2(){
cout << "Mid2:Mid2()" << endl;
}
};
class Child:public Mid1,public Mid2{
public:
Child(){
cout << "Child:Child()" << endl;
}
};
int main(void){
Child d;
//d.print() << endl;报错,这样使用会产生二义性
d.Mid1::print();//ok
d.Mid2::print();//ok
return 0;
}Base::Base()1
Mid1::Mid1()
Base::Base()2
Mid2::Mid2()
Child::Child()
在实例化,Child对象时,先会调用Mid1和Mid2构造函数,Mid1和Mid2分别继承与Base,所以
Base最终被调用了两次.
虚继承
#include <iostream>
using namespace std;
int gFlag = 0;
class Base{
public:
Base(){
cout << "Base::Base()"<<++gFlag << endl;
}
void print(){
cout << "Base::print()" << endl;
}
};
class Mid1:virtual public Base{
public:
Mid1(){
cout << "Mid1::Mid1()" << endl;
}
};
class Mid2:virtual public Base{
public:
Mid2(){
cout << "Mid2::Mid2()" << endl;
}
};
class Child:public Mid1,public Mid2{
public:
Child(){
cout << "Child::Child()" << endl;
}
};
int main(void){
Child d;
d.print();
return 0;
}Base::Base()1
Mid1::Mid1()
Mid2::Mid2()
Child::Child()
Base::print()
虚继承,会共享子类通过虚继承的基类的内存,Mid1调用实例化了一次Base,Mid2构造时,就没有再次
实例化Base,Mid1和Mid2共享基类Base的内存.
虚继承,解决了二义性问题,也节省了内存.
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