My test program from learning "move constructor", "move assignment". For personal memo purpose.-优快云博客

本文深入探讨了C++中类成员赋值操作的原理，详细解析了拷贝构造函数、赋值运算符的实现方式，并对比了深拷贝与浅拷贝的区别，通过实例代码展示了如何正确地进行赋值操作。

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#include <iostream>
#include <string>

/*
When it comes to move assignment, we cannot just use std::swap(*this, rhs);
It is because std::swap combines with three std::move commands: one is a move
constructor, the other two are move assignments. So it will result in endless
recursion from call move assignment within move assignment.
*/

using std::cin; using std::cout; using std::endl;

class MetaData
{
public:
    MetaData (int size, const std::string& name)
        : _name( name )
        , _size( size )
    {
    	cout << "MetaData initialiser!" << endl;
    }
 
    // copy constructor
    MetaData (const MetaData& other)
        : _name( other._name )
        , _size( other._size )
    {
    	cout << "MetaData copy constructor!" << endl;
    }
 
    // move constructor
    MetaData (MetaData&& other)
        : _name( std::move(other._name) )
        , _size( other._size )
    {
    	cout << "MetaData move constructor!" << endl;
    }
	
	MetaData &operator= (MetaData &other)
	{
		if(this != &other)
		{
			_name = other._name;
			_size = other._size;
		}

		cout << "MetaData copy assignment!" << endl;
		return *this;
	}
 
 	MetaData &operator= (MetaData &&other)
	{
		if(this != &other)
		{
			_name = other._name;
			_size = other._size;
			other._name = "";
			other._size = 0;
		}
		
		cout << "MetaData move assignment!" << endl;
		return *this;		
	}
 
    std::string getName () const { return _name; }
    int getSize () const { return _size; }

private:
    std::string _name;
    int _size;
};



class ArrayWrapper
{
public:
    // default constructor produces a moderately sized array
    ArrayWrapper ()
        : _p_vals( new int[ 64 ] )
        , _metadata( 64, "ArrayWrapper" )
    {}
 
    ArrayWrapper (int n)
        : _p_vals( new int[ n ] )
        , _metadata( n, "ArrayWrapper" )
    {}
 
    // move constructor
    ArrayWrapper (ArrayWrapper&& other)
        : _p_vals( other._p_vals  )
        , _metadata( std::move(other._metadata) )
    {
        cout << "ArrayWrapper move constructor!" << endl;
		other._p_vals = NULL;
    }
 
    // copy constructor
    ArrayWrapper (const ArrayWrapper& other)
        : _p_vals( new int[ other._metadata.getSize() ] )
        , _metadata( other._metadata )
    {
        for ( int i = 0; i < _metadata.getSize(); ++i )
        {
            _p_vals[ i ] = other._p_vals[ i ];
        }
    }
    ~ArrayWrapper ()
    {
        delete [] _p_vals;
    }
private:
    int *_p_vals;
    MetaData _metadata;
};



class Integer
{
public:
	Integer(int n, std::string s):elem(n),str(s)
	{
		cout << "Integer initialiser!" << endl;
	}
	
	Integer(const Integer &val):elem(val.elem)
	{
		str = "COPY";
		cout << "Integer copy constructor!" << endl;
	}
	Integer(Integer &&val):elem(val.elem)
	{
		str = "MOVE";
		cout << "Integer move constructor!" << endl;
	}
	Integer &operator=(const Integer &val)
	{
		cout << "****** Integer copy assignment begins! ******" << endl;
		// if(this != &val)
		// {
		// 	elem = val.elem;
		// 	str = val.str;
		// 	cout << "Integer copy assignment!" << endl;
		// }
		Integer copy = val;
		std::swap(*this, copy);
		cout << "********* Integer copy assignment ends *******" << endl;
		return *this;
	}
	Integer &operator=(Integer &&val)
	{
		cout << "******* Integer move assignment begins! *******" << endl;
		std::swap(elem, val.elem);
		std::swap(str, val.str);
		cout << "******* Integer move assignment ends! *******" << endl;
		return *this;
	}
	
	std::string getVal()
	{
		return str;
	}
private:
	int elem;
	std::string str;
};

Integer ret()
{
	Integer tmp(100, "tmp");
	return tmp;
}

int main()
{
	// ArrayWrapper aw1;
	// ArrayWrapper aw3(aw1);

	Integer i1(99,"i1");
	Integer i2(100,"i2");
	// cout << i2.getVal() << endl;
	i2 = {1, "haha"};
	cout << endl;
	i2= i1;
	cout << i2.getVal() << endl;
	return 0;
}