C++；构造函数调用 我在C++中编写了这个小代码片段，输出也附上了。 我无法理解为什么构造函数只被调用一次，而我可以看到对析构函数进行了两次调用

据我所知，应该在第28行调用默认构造函数和重载赋值运算符

有人能解释一下吗：

  1 #include <iostream>
  2 using namespace std;
  3 
  4 class ABC {
  5   char c;
  6   public:
  7     ABC() {
  8       cout << "default" << endl;
  9     }
 10     ABC(char c) {
 11       this->c = c;
 12       cout << c << endl;
 13     }
 14     ~ABC() {
 15       cout << hex << this << " destructor " << c << endl;
 16     }
 17     void method() {
 18       cout << "method" << endl;
 19     }
 20     void operator= (const ABC& a) {
 21       cout << "operator" << endl;
 22     }
 23
 24 };
 25 
 26 int main() {
 27   ABC b('b');
 28   ABC a = b;
 29 }

这是一个复制构造函数而不是赋值运算符！您可以这样重新定义它，您拥有的是编译器生成的一个：

ABC(const ABC& other)
{
 c = other.c;
 cout << c << " copy constructor" << endl;
}

---

刚才调用复制构造函数的代码，定义如下：

ABC(const ABC& a):c(a.c){
    cout << "copying " << hex << &a << endl;
}

如果要调用默认构造函数，然后调用赋值运算符，则必须使用两个单独的语句：

  ABC b('b');
  ABC a;
  a = b;

---

请查看您的系统的修改代码

#include <iostream>
using namespace std;
class ABC {
    char c;
public:

    ABC() {
        cout << "default" << endl;
    }
        ABC(char c)
        {
            cout<<"parameterized constructor called\n";/////overloaded constructor called for the first line in main
            this->c = c;
            cout << c << endl;
        }
        ABC(ABC &c)
        {
            cout<<"Copy cons\n";//copy constructor is called for the second line in main
        }


        ~ABC() {
            cout << hex << this << " destructor " << c << endl;
        }
        void method() {
            cout << "method" << endl;
        }
        void operator= (const ABC& a) {

        }


    };


int main()
{
        ABC b('b');//////here parameterized constructor is called i.e <ABC(char c)>
        ABC a = b;/////////Here the copy constructor is called not the default one.(total 2 object created so the destructor is called twice!)
}

现在让我们解释一下原因 在3种情况下调用复制构造函数 1.初始化中的对象时 2.当对象作为参数传递给函数时 3.从函数返回对象时

如果您没有指定自己的复制构造函数，那么编译器将实现自己的复制构造函数，它将逐位复制对象。您没有指定自己的复制构造函数，因此无法跟踪从代码创建的两个对象。

---

谢谢

更好的是，你可以使用一个初始化列表。是的，就像现在一样，复制构造函数在你的代码中包含一个对

c

赋值操作符的调用确保你不做转换操作符，我提到它只是为了好玩，不是为了这个例子：）构造函数标记有什么问题？

ABC(const ABC& a):c(a.c){
    cout << "copying " << hex << &a << endl;
}

b
copying 0x7fffebc0e02f
0x7fffebc0e02e destructor b
0x7fffebc0e02f destructor b

  ABC b('b');
  ABC a;
  a = b;

#include <iostream>
using namespace std;
class ABC {
    char c;
public:

    ABC() {
        cout << "default" << endl;
    }
        ABC(char c)
        {
            cout<<"parameterized constructor called\n";/////overloaded constructor called for the first line in main
            this->c = c;
            cout << c << endl;
        }
        ABC(ABC &c)
        {
            cout<<"Copy cons\n";//copy constructor is called for the second line in main
        }


        ~ABC() {
            cout << hex << this << " destructor " << c << endl;
        }
        void method() {
            cout << "method" << endl;
        }
        void operator= (const ABC& a) {

        }


    };


int main()
{
        ABC b('b');//////here parameterized constructor is called i.e <ABC(char c)>
        ABC a = b;/////////Here the copy constructor is called not the default one.(total 2 object created so the destructor is called twice!)
}

parameterized constructor called
b
Copy cons
0x7fff5fbff820 destructor �
0x7fff5fbff828 destructor b