复制构造函数未调用!

Question

我不明白为什么在这种情况下不会调用复制构造函数.有人可以解释一下吗？

#include <iostream>

class foo
{
    int* ptr;
    public:
    foo()
    {
        std::cout << "\n Constructor \n" ;
        ptr  = new int;
        *ptr = 10;
    }

    foo( const foo* &obj )  // Copy Constructor
    {
         std::cout << "\n Copy Constructor \n" ;
         ptr  = new int;
         *(this->ptr) = *(obj->ptr);
    }

    // Copy Assignment Operator

    ~foo()  // Destructor
    {
        delete ptr;
    }
};

int main()
{
    foo* objOne = new foo;
    foo* objTwo = objOne ;

    getchar();
    return 0;
}

Answer 1

因为你只是创建另一个指针到同一个对象,而不是一个新的对象:

foo* objOne = new foo;
foo* objTwo = objOne;
   ^
   |
   +-- these are pointers.

如果您想要一个新对象,请使用以下内容:

foo objTwo = objOne;

并修复您的复制构造函数:

foo (const foo &obj) ...

以下代码段显示了一种方法:

#include <iostream>

class foo {
    public:

    foo () {
        std::cout << "constructor" << std::endl;
        ptr  = new int;
        *ptr = 10;
    }

    foo (const foo &obj) {
        std::cout << "copy constructor" << std::endl;
        ptr  = new int;
        *(this->ptr) = *(obj.ptr);
    }

    ~foo () {
        delete ptr;
    }

    private:

    int* ptr;
};

int main()
{
    foo objOne;
    foo objTwo = objOne ;
    return 0;
}

这输出:

constructor
copy constructor

正如你所料.