构造函数的写法

最新推荐文章于 2025-10-08 12:23:23 发布

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#构造函数

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本文通过一个C++示例展示了构造函数、拷贝构造函数及赋值运算符的调用过程。通过对不同构造函数的地址输出，揭示了对象创建与复制时的内部机制。

猜一下输出是啥?

#include <iostream>

class ConstructorChecker
{
  public:
    ConstructorChecker(int m) : _m(m)
    {
        std::cout << "this is construct in addr: " << (unsigned long)this << std::endl;
        std::cout << "******************************" << std::endl;
    };

    ConstructorChecker(const ConstructorChecker &other)
    {
        _m = other._m;
        std::cout << "this is construct in addr: " << (unsigned long)this << " from other " << (unsigned long)&other << std::endl;
        std::cout << "now value is " << _m << std::endl;
        std::cout << "******************************" << std::endl;
    };

    ConstructorChecker &operator=(const ConstructorChecker &other)
    {
        _m = other._m;
        std::cout << "assignment operator..." << std::endl;
        return *this;//这个return *this 是必须的,否则将会有未定义行为
        std::cout << "******************************" << std::endl;
    };

  private:
  public:
  private:
    int _m;
};

int main()
{
    ConstructorChecker firstConstructorChecker(100);
    ConstructorChecker secondConstructorChecker = firstConstructorChecker;
    ConstructorChecker thirdConstructorChecker(1234);
    secondConstructorChecker = thirdConstructorChecker;
}

this is construct in addr: 140732886930616
******************************
this is construct in addr: 140732886930608 from other 140732886930616
now value is 100
******************************
this is construct in addr: 140732886930600
******************************
assignment operator...