在 C++ 中使用指向对象的指针和 operator new 来定义对象

Question

关于使用指向对象的指针定义对象的简单示例。我们定义一个对象 A *a = new A(123.4); 然后另一个对象 A *b = new A(*a);

我不明白的是，这对 b（指向）对象究竟是如何工作的？复制构造函数如何在这里启动并将值初始化为与对象 a 相同的值？我认为为了让它起作用，我们应该在 class.

中声明一个自定义复制构造函数

#include <iostream>
using namespace std;

class A {
public:
    A(float v) { A::v = v; }
    float v;
    float set(float v) {
        A::v = v;
        return v;
    }
    float get(float v) {
        return A::v;
    }
};

int main() {
    A *a = new A(123.4);
    A *b = new A(*a);

    cout << a->v << endl;
    cout << b->v << endl;

    a->v = 0.0;
    cout << a->v << endl;
    cout << b->v << endl;

    b->v = 1.0;
    cout << a->v << endl;
    cout << b->v << endl;

    return 0;
}

程序的输出是：

提前致谢。

Answer 1

编译器为您生成了复制构造函数。它将执行成员变量的浅拷贝，这对你的情况来说已经足够了。

来自Wikipedia：

Special member functions in C++ are functions which the compiler will automatically generate if they are used, but not declared explicitly by the programmer. The special member functions are:

Default constructor (if no other constructor is explicitly declared)

Copy constructor if no move constructor or move assignment operator is explicitly declared. If a destructor is declared, generation of a copy constructor is deprecated.

Move constructor if no copy constructor, move assignment operator or destructor is explicitly declared.

Copy assignment operator if no move constructor or move assignment operator is explicitly declared. If a destructor is declared, generation of a copy assignment operator is deprecated.

Move assignment operator if no copy constructor, copy assignment operator or destructor is explicitly declared.

Destructor

在 C++ 中使用指向对象的指针和 operator new 来定义对象

Defining an object with a pointer to an object and operator new in c++

c++

polymorphism

object