C++ 复制/移动构造函数和赋值运算符

Question

想了解C++的copy/move构造函数和赋值运算符，先举个代码例子:

标题:

class Person
{
public:
    Person();
    Person(const char * name, int age);
    Person(const Person &person);
    Person(Person&&) noexcept;

    virtual ~Person();

    Person &operator=(const Person & other);
    Person &operator=(Person &&other) noexcept;

    char *getName() const;
    int getAge() const;

private:
    char *name;
    int age = 0;
};

来源:

Person::Person() : age(0)
{
    this->name = new char[100];
    memset(this->name, 0, sizeof(char)*100);
}

Person::Person(const char * name, int age) : Person()
{
    std::strcpy(this->name, name);
    this->age = age;
}

Person::Person(const Person &person)
{
    if(this == &person)
    {
        return;
    }
    //delete[](name);
    this->name = new char[100];
    memset(this->name, 0, sizeof(char)*100);
    std::strcpy(name, person.name);
    age = person.age;
}

Person::Person(Person &&other) noexcept
{
    if(this == &other)
    {
        return;
    }
    //delete[](name);
    name = other.name;
    age = other.age;
    other.name = nullptr;
    other.age = 0;
}

Person &Person::operator=(const Person &other)
{
    if(this == &other)
    {
        return *this;
    }
    delete[](name);
    name = new char[100];
    memset(name, 0, sizeof(char)*100);
    std::strcpy(name, other.name);
    age = other.age;
    return *this;
}

Person &Person::operator=(Person &&other) noexcept
{
    if(this == &other)
    {
        return *this;
    }
    delete[](name);
    name = other.name;
    age = other.age;
    other.name = nullptr;
    other.age = 0;
    return *this;
}

Person::~Person() {
    delete[](name);
    name = nullptr;
}

现在的问题是:如果 this= =&其他？因为它是一个构造函数，不可能与其他的相等。并且是否需要在 copy 和 move 构造函数中我们delete(释放)内存？因为内存还没有分配，那为什么要删除呢？我这样说是因为我在很多C++教程中看到他们删除内存并检查是否相等。

所以如果我是对的，那么copy和move构造函数可以这样写:

Person::Person(const Person &person) : Person()
{
    std::strcpy(name, person.name);
    age = person.age;
}
Person::Person(Person &&other) noexcept
{
    name = other.name;
    age = other.age;
    other.name = nullptr;
    other.age = 0;
}

还有如何检查移动赋值中的相等性？

Person &Person::operator=(Person &&other) noexcept

谢谢!

Answer 1

I want to know about C++ copy/move constructor and equal operator...

我认为您指的是赋值运算符 operator=。等于运算符将是 operator==。

Does it really need in the copy and move constructors that we check for equality if this==&other?

不，您已经说过不需要这个。

Does it need that in the copy and move constructors we delete (free) the memory?

您将在移动和复制分配中需要它，因为您必须释放旧内存才能复制(或仅设置指针)另一个Person 的内存。您的构造函数不需要删除。

So if I am right, then the copy and move constructor can be written like this

是的，这些都是正确的。您确定要为每个人固定 100 个字节吗？

And also how about checking for equality in move assignment?

我不会检查移动分配中的相等性，因为移动是一种非常便宜的操作，而且您不太可能分配相同的对象。