C++学习笔记 lesson4 构造函数2

来源：互联网发布：淘宝工作室是怎么赚钱编辑：程序博客网时间：2024/05/16 16:08
#include<iostream> class ClassDemo{public:ClassDemo() {std::cout << "ClassDemo()...被调用" << _num << std::endl;};ClassDemo(int num):_num(num){std::cout << "ClassDemo("<< _num<<")...被调用" << std::endl;};~ClassDemo() {std::cout << "~ClassDemo()...被调用" << _num << std::endl;};ClassDemo & operator=(const ClassDemo&other){std::cout << " operator=(const ClassDemo&)...被调用" << _num << std::endl;_num = other._num;return *this;}ClassDemo(const ClassDemo&other)//拷贝构造函数 参数为引用{std::cout << "ClassDemo(ClassDemo&)...被调用" << _num << std::endl;_num = other._num;}//ClassDemo(const ClassDemo other) 无限递归，编译无法通过//将形参int GetNum() const{return _num;};private:int _num;};void F1(ClassDemo demo) //调用拷贝构造函数产生的临时对象{demo.GetNum(); //，使用的是临时对象//销毁了临时对象 }void F2(const ClassDemo&demo)  {demo.GetNum(); //只能调用const方法}int main(){ClassDemo demo = 10;//调用默认构造demo = 20; //==>demo.operator=(ClassDemo(20)) 打印出的_num是调用方的_num//调用默认构造temp//调用默认operator=(const ClassDemo&other)    //调用析构ClassDemo demo1 = demo;//ClassDemo(ClassDemo&)被调用ClassDemo   demo1(10);// ClassDemo(10)...被调用F1(demo1);   //产生了新的临时对象// ClassDemo(&)...被调用//~ClassDemo()...被调用10F2(demo1); //没有新的对象产生return 0;//~ClassDemo()...被调用10}  //空类中的方法class ClassDemo{  //默认无参构造// ClassDemo(){}  //默认析构// ~ClassDemo(){}  //默认拷贝构造// ClassDemo(const ClassDemo& other){}  //默认赋值// ClassDemo& operatot=(const CLassDemo other){}//如果有属性private:int _num;//默认拷贝构造// ClassDemo(const ClassDemo& other){num=other._num}//默认赋值// ClassDemo& operatot=(const CLassDemo other){num=other._num}};class MyString{public:MyString(){_len = 100;_str = new char[_len];}MyString(const char*str) :_len(strlen(str)){_str = new char[_len + sizeof(char)];strcpy(_str, str);}~MyString(){if (_str)delete[]_str;}MyString(const MyString & other){delete[]_str;_len = other._len;_str = new char[_len + sizeof(char)];strcpy(_str, other._str); //深拷贝 在对象中，维护了所有参数的生命周期，所有参数的生命周期和我的对象同步  //_str = other._str; //浅拷贝：直接对指针赋值 的行为,存在风险，指针的赋值被delete//_len = other._len; //没有维护参数的生命周期，给别人来维护了}char *GetString(){return _str;}private:char *_str; //有指针的情况int _len;};void test(){MyString  str("I love Mark");MyString sb = str;//拷贝构造std::cout << sb.GetString() << std::endl;sb = "I Need Mark!!";    // 产生临时对象，//对sb进行赋值 operator(MyString&)(sb._str=temp._str;_len=temp.len)//析构临时对象temp delete temp._str ==》等同于  delete sb._str(指向同一块区域，已经被释放了，野指针)std::cout << sb.GetString() << std::endl;}
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