派生类构造函数与析构函数的结构规则
派生类构造函数与析构函数的构造规则
1.派生类的构造函数可以不显示式的写出基类的构造函数。例如:
Third()
{e=0;}
此时,系统自动调用基类的无参构造函数(没有,则为默认的构造函数)。也可显示式的指出调用基类的哪一个构造函数。例如:
Third(int x,int y,int z):Second(x,y)
{
e=z;
}
2.要调用的基类构造函数的参数可在派生类的构造函数中明确给出。例如:
Third(int x,int y,int z):Second(x,y)
{
e=z;
}
也可不给出:
Second():First(1,1)
{
c=0;
d=0;
}
还可以对派生类构造函数的参数进行一些交换,再传递给要调用的基类的构造函数,例如:
Second(int x,int y):First(x+1,y+1)
{
c=x;
d=y;
}
一个完整的例子如下:
#include<iostream> using namespace std; class First{ public: First() { a=0; b=0; } First(int x,int y) {a=x; b=y; } ~First() { cout<<"destructing First"<<endl; } void show() { cout<<"\n a="<<a<<"\n b="<<b<<endl; } private: int a; int b; }; class Second:public First{ public: Second():First(1,1) { c=0; d=0; } Second(int x,int y):First(x+1,y+1) { c=x; d=y; } Second(int x,int y,int m,int n):First(m,n) { c=x; d=y; } ~Second() { cout<<"destructing Second"<<endl; } void show() { First::show(); cout<<"c="<<c<<"d="<<d<<endl; } private: int c,d; }; class Third:public Second{ public: Third() {e=0;} Third(int x,int y,int z):Second(x,y) { e=z; } Third(int x,int y,int z,int m,int n):Second(x,y,m,n) { e=z; } ~Third() { cout<<"destructing Third"<<endl; } void show() { Second::show(); cout<<"e="<<e<<endl; } private: int e; }; int main() { First f; f.show(); cout<<"======================"<<endl; Second d1; d1.show(); cout<<"======================"<<endl; Second d2(10,20,30,40); d2.show(); cout<<"====================="<<endl; Second d3(12,13); d3.show(); cout<<"======================="<<endl; Third t; t.show(); cout<<"======================"<<endl; Third t1(14,15,16); t1.show(); cout<<"======================="<<endl; Third t2(50,60,70,80,90); t2.show(); return 0; }