[英]Overloading copy assignment operator
我最近一直在学习重载运算符,并很快来到重载复制运算符。 我尝试了一些示例,但无法真正理解其格式及其功能。 好吧,如果您可以用更简单的方式向我解释代码,这将很有帮助,因为因为我是C ++的初学者。 无论如何,这是我的代码:
#include <iostream>
using namespace std;
class Point{
private:
int* lobster;
public:
Point(const int somelobster){
lobster = new int;
*lobster = somelobster;
}
//deep copy
Point(const Point& cpy){ //copy of somelobster(just to make sure that it does not do shallow copy)
lobster = new int;
*lobster = *cpy.lobster;
}
//assingment operator
Point& operator=(const Point& cpy){ //used to copy value
lobster = new int; //same thing as the original overloaded constructor
*lobster = *cpy.lobster; //making sure that it does not makes a shallow copy when assigning value
return *this;
}
void display_ma_lobster(){ //display nunber
cout << "The number you stored is: " << *lobster << endl;
}
~Point(){ //deallocating memory
cout << "Deallocating memory" << endl;
delete lobster;
}
};
int main(){
Point pnt(125);
cout << "pnt: ";
pnt.display_ma_lobster();
cout << "assigning pnt value to tnp" << endl;
Point tnp(225);
tnp = pnt;
tnp.display_ma_lobster();
return 0;
}
但是真正需要解释的主要部分是:
//deep copy
Point(const Point& cpy){ //copy of somelobster(just to make sure that it does not do shallow copy)
lobster = new int;
*lobster = *cpy.lobster;
}
//assingment operator
Point& operator=(const Point& cpy){ //used to copy value
lobster = new int; //same thing as the original overloaded constructor
*lobster = *cpy.lobster; //making sure that it does not makes a shallow copy when assigning value
return *this;
}
感谢您的时间
副本分配运算符可以使用对象已拥有的现有资源。 它不像构造函数。 (您的副本构造函数是正确的。)
//assingment operator
Point& operator=(const Point& cpy){ //used to copy value
// Do not allocate anything here.
// If you were to allocate something, that would require deallocating yer shit too.
*crap = *cpy.crap; //making sure that it does not makes a shallow copy when assigning value
return *this;
}
关于该主题的不错的阅读是: 什么是复制和交换惯用法?
对象包含已分配的内存,因此,每次复制对象时,还需要执行新的内存分配,并复制分配的内容。 这就是为什么在复制构造函数中需要这些东西的原因。 当编译器尝试复制您的对象(例如跨函数调用)并将其放置在容器中时,将自动调用复制构造函数。
赋值运算符有缺陷,因为它需要做的更多或更少。 它用于
tnp = pnt;
因为它正在处理将一个对象分配给另一个对象,所以它需要使用现有的已分配内存,或者在复制pnt内存之前处理旧tnp对象中的内存释放。
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