作者:非妃是公主
专栏:《笔记》《C++》
个性签:顺境不惰,逆境不馁,以心制境,万事可成。——曾国藩
构造函数调用顺序为:先按照继承关系中基类的声明顺序调用基类构造函数,再按照,本类成员的声明顺序进行构造。
而虚继承是其中的一个反例。
无虚继承的代码:
#include<iostream>
using namespace std;
class B1 {
public:
B1(int i) { cout << "constructing B1 " << i << endl; }
~B1() { cout << "destructing B1 " << endl; }
};
class B2 {
public:
B2() { cout << "constructing B3 * " << endl; }
~B2() { cout << "destructing B3" << endl; }
};
class C :public B2, public B1 {//此处采用普通继承
int j;
public:
C(int a, int b, int c) :B1(a), memberB1(b), j(c) {}
private:
B1 memberB1;
B2 memberB2;
};
int main() {
C obj(1, 2, 3);
}
执行结果:
constructing B3 *
constructing B1 1
constructing B1 2
constructing B3 *
destructing B3
destructing B1
destructing B1
destructing B3
有虚继承代码:
#include<iostream>
using namespace std;
class B1 {
public:
B1(int i) { cout << "constructing B1 " << i << endl; }
~B1() { cout << "destructing B1 " << endl; }
};
class B2 {
public:
B2() { cout << "constructing B3 * " << endl; }
~B2() { cout << "destructing B3" << endl; }
};
class C :public B2, virtual public B1 {//此处改为虚继承
int j;
public:
C(int a, int b, int c) :B1(a), memberB1(b), j(c) {}
private:
B1 memberB1;
B2 memberB2;
};
int main() {
C obj(1, 2, 3);
}
执行结果:
constructing B1 1
constructing B3 *
constructing B1 2
constructing B3 *
destructing B3
destructing B1
destructing B3
destructing B1
结论:虚基类构造函数优先执行。
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