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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;
}
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//砖石继承,二义性
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#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;
}
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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
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#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;
}
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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.
本文转自神ge 51CTO博客，原文链接:http://blog.51cto.com/12218412/1867815
