拷贝赋值：两个对象之间的拷贝
默认拷贝赋值导致错误
#include <iostream>
class A {
public:
A(int i=10){
m_pi = new int(i);
ii = i;
}
A(const A& that) {
std::cout << "深拷贝构造函数" << std::endl;
m_pi = new int;
*m_pi = *that.m_pi;
}
void print(void) {
std::cout << ii << std::endl;
}
~A(void) {
std::cout << "xigouhansu："<<this << std::endl;
delete m_pi;
}
private:
int* m_pi;
int ii;
};
int main()
{
A a(100);
A b;
b.print();
//b.operator=(a);
b = a;//拷贝赋值；与b.operator=(a)等价
//拷贝赋值：两个对象已经存在
//编译器其实执行函数：b.operator=(a);
//如果程序没写这个函数，会执行默认的，在执行析构函数时导致程序中断
//中断原因:默认的拷贝赋值是直接拷贝各个成员变量值；由于m_pi是指针，a和b指向同一个堆区数据，不能delete两次
//所以当存在指针类型的成员变量时，要自己写b.operator=(a)函数
b.print();
}
自写拷贝赋值函数
#include <iostream>
class A {
public:
A(int i=10){
m_pi = new int(i);
ii = i;
}
A(const A& that) {
std::cout << "senkaobei" << std::endl;
m_pi = new int;
*m_pi = *that.m_pi;
}
A& operator=(const A&that) { //自写拷贝赋值函数
if (&that != this) { //防止自赋值
*m_pi = *that.m_pi; //拷贝指针的数据
ii = that.ii;
}
return *this; //返回自身引用
}
void print(void) {
std::cout << ii << std::endl;
std::cout << *m_pi << std::endl;
}
~A(void) {
std::cout << "xigouhansu："<<this << std::endl;
delete m_pi;
}
private:
int* m_pi;
int ii;
};
int main()
{
A a(100);
A b;
b.print();
b = a; //拷贝赋值
std::cout << &a << std::endl;
std::cout << &b << std::endl;
b.print();
}
