构造函数和析构函数 <三>

/****** 1.构造函数初始化列表******/#include<iostream>using namespace std;class Test{public:   Test():p(new int[size]),size(10)//初始化列表初始化变量size和指针p，注意顺序    {    cout<<"new obj creat succes!"<<endl;    for(int i=1;i<=size;i++)        p[i]=i;        cout<<"size = "<<size<<endl;        for(int i=1;i<=size;i++)     cout<<p[i]<<" ";cout<<endl;    }     ~Test()    {        cout<<"obj has been destoryed!"<<endl;    }private:        //这里若是先定义*P后定义size好像对程序运行没影响    int size;   //因为如果先定义*p，那new运算符就不知道该为*p分配多少空间了    int *p;     //这点我很好奇。};int main(){  Test a;    return 0;}

程序结果：

 

利用构造函数初始化列表初始化了size和指针*p，然后对指针p所指的区域赋值，最后打印并撤销对象。

/****** 2.构造函数初始化列表与静态变量******/#include<iostream>using namespace std;int a=8;int b=6;int c=7;class Test{public:   Test():p(&a)//让p指向a    {    cout<<"new obj creat succes!"<<endl;    for(int i=0;i<3;i++)        p[i]=i;//对指针所指区域赋值        for(int i=0;i<3;i++)     cout<<p[i]<<" ";cout<<endl;    }     ~Test()    {        cout<<"obj has been destoryed!"<<endl;    }private:    int size;    int *p;};int main(){  Test s;  cout<<"a= "<<a<<" and,a address is "<<&a<<endl;//打印a,b,c的值和地址  cout<<"b= "<<b<<" and,b address is "<<&b<<endl;  cout<<"c= "<<c<<" and,c address is "<<&c<<endl;    return 0;}

程序结果：

这里a,b,c是静态变量，他们在分配时的地址是连续的，初始化*p时让p指向a，让后修改p指向的内容，程序运行结果可以看到

a,b,c的值发生了改变，但地址是连续的。

/****** 3.对象成员初始化顺序******/#include<iostream>using namespace std;class Test1{public:   Test1()    {    cout<<"Test1 obj creat succes!"<<endl;    }     ~Test1()    {        cout<<"Test1 obj has destoryed!"<<endl;    }private:    int size;};class Test2{public:   Test2()    {        cout<<"Test2 obj creat succes!"<<endl;    }     ~Test2()    {        cout<<"Test2 obj has destoryed!"<<endl;    }private:    Test1 num;//Test2对象的私有成员是Test1的一个对象};int main(){  Test2 s;  return 0;}

程序运行结果：

 

创建对象Test2 s时，对象s的私有成员num被创建，然而num是Test1的一个对象，所以Test1的构造函数先被调用

然后Test2的构造函数被调用，析构恰好与之相反。

/*********4.多对象的构造函数、析构函数顺序***/#include<iostream>using namespace std;class Test1{public:   Test1(int nu):num(nu)    {        cout<<"num = "<<num<<endl;    cout<<num<<" creat success!"<<endl;    }     ~Test1()    {        cout<<num<<" has destoryed!"<<endl;    }private:    int num;};class Test2{public:   Test2():obj2(13),obj1(12)//带参数初始化Test1的两个对象    {        cout<<"Test2 obj creat succes!"<<endl;    }     ~Test2()    {        cout<<"Test2 obj has destoryed!"<<endl;    }private:    Test1 obj1;//Test2对象的私有成员是Test1的对象    Test1 obj2;//构造函数的顺序与定义顺序有关，与初始化无关};int main(){  Test2 s;  return 0;}

程序运行结果：

可以看出，Test1的obj1先被创建，obj2后被创建；

/*******5.对象的构造按定义的顺序，与初始化顺序无关****/#include<iostream>using namespace std;class Test1{public:   Test1(int nu):num(nu)    {        cout<<"num = "<<num<<endl;    cout<<num<<" creat success!"<<endl;    }     ~Test1()    {        cout<<num<<" has destoryed!"<<endl;    }private:    int num;};class Test2{public:   Test2(int n,int p):obj2(p),obj1(n)    {        cout<<"Test2 obj creat succes!"<<endl;    }     ~Test2()    {        cout<<"Test2 obj has destoryed!"<<endl;    }private:    Test1 obj1;//Test2对象的私有成员是Test1的一个对象    Test1 obj2;//注意定义的顺序，对象的构造按定义的顺序，与初始化顺序无关};int main(){  Test2 s(35,36);  return 0;}

运行结果：

/******6.对象中常量的初始化只能在初始化列表中******/#include<iostream>using namespace std;class Test1{public:   Test1()    {        num=14;//常量的赋值不是以初始化列表形式，不被允许        cout<<"num = "<<num<<endl;    cout<<num<<" creat success!"<<endl;    }     ~Test1()    {        cout<<num<<" has destoryed!"<<endl;    }private:    const int num;};int main(){  Test1 s;  return 0;}

程序运行结果：

 

程序编译不通过

/****** 7.对象中常量的初始化只能在初始化列表中******/#include<iostream>using namespace std;class Test1{public:   Test1():num(14)//初始化列表初始化const常量    {        cout<<"num = "<<num<<endl;    cout<<num<<" creat success!"<<endl;    }     ~Test1()    {        cout<<num<<" has destoryed!"<<endl;    }private:    const int num;//const变量num};int main(){  Test1 s;  return 0;}

运行结果：

/****** 8..对象中引用成员的初始化也只能在初始化列表中******/#include<iostream>using namespace std;class Test1{public:   Test1():num(14)    {    nu=num;//非初始化列表赋值引用型变量，不允许    cout<<"num = "<<num<<endl;    cout<<num<<" creat success!"<<endl;    cout<<"nu = "<<nu<<endl;    cout<<nu<<" creat success!"<<endl;    }     ~Test1()    {        cout<<num<<" has destoryed!"<<endl;    }private:     int num;    int& nu;};int main(){  Test1 s;  return 0;}

编译出错：

/******9. 对象中引用成员的初始化也只能在初始化列表中******/#include<iostream>using namespace std;class Test1{public:   Test1():num(14),nu(num)//初始化列表初始化引用变量    {    //nu=num;    cout<<"num = "<<num<<endl;    cout<<num<<" creat success!"<<endl;    cout<<"nu = "<<nu<<endl;    cout<<nu<<" creat success!"<<endl;    }     ~Test1()    {        cout<<num<<" has destoryed!"<<endl;    }private:     //const int num;编译报错，不能将常量赋值给引用，纳闷   Int num; int& nu;};int main(){  Test1 s;  return 0;}

运行结果：

可以看到，程序中用初始化列表定义了num变量，然后将num变量赋值给引用型变量nu,值得注意的是

如果num声明为const，编译不通过，即不允许这样的赋值操作。