为什么析构函数在这里被调用两次？

Question

我无法理解为什么第二个对象d2的析构函数被调用两次.我知道过去曾问过这类问题,但每一个问题都有一些与我相关的差异.任何帮助将不胜感激.谢谢.

#include <iostream>
using namespace std;

class data{
char s1[50];
static int j;
public:
    data(char s[50]){
        for(int i = 0; i < 50; i++){
            s1[i] = s[i];
        }
    }
    void show(){
        cout <<"Data " << ++j <<"=" << s1 << endl;
    }
    void compare(data d){
        for(int i = 0; i < 50; i++){
            if(d.s1[i] != s1[i]){
                cout << "Both Objects have different text." << endl;
                break;
            }
        }
    }
    ~data(){
        cout << "Release memory allocated to " << s1 << endl;
    }
};
int data::j;
int main(){
    char str[50],str1[50];
    cin>>str;
    cin>>str1;

    data d1(str);
    data d2(str1);

    d1.show();
    d2.show();

    d1.compare(d2);

    return 0;

}

此代码运行时的输出是:

 Data 1=object1
 Data 2=object2
 Both Objects have different text.
 Release memory allocated to object2
 Release memory allocated to object2
 Release memory allocated to object1    

Answer 1

因为您将输入参数传递给compare值而不是引用.