cpp/CPPlusV6/Chapter 18/stdmove.cpp

// stdmove.cpp -- using std::move()
#include <iostream>
#include <utility>
// use the following for g++4.5
// #define nullptr 0
// interface
class Useless
{
private:
    int n;          // number of elements
    char * pc;      // pointer to data
    static int ct;  // number of objects
    void ShowObject() const;
public:
    Useless();
    explicit Useless(int k);
    Useless(int k, char ch);
    Useless(const Useless & f); // regular copy constructor
    Useless(Useless && f);      // move constructor
    ~Useless();
    Useless operator+(const Useless & f)const;
    Useless & operator=(const Useless & f); // copy assignment
    Useless & operator=(Useless && f);      // move assignment 
    void ShowData() const;
};

// implementation
int Useless::ct = 0;

Useless::Useless()
{
    ++ct;
    n = 0;
    pc = nullptr;
 }

Useless::Useless(int k) : n(k)
{
    ++ct; 
    pc = new char[n];
}

Useless::Useless(int k, char ch) : n(k)
{
    ++ct;
    pc = new char[n];
    for (int i = 0; i < n; i++)
        pc[i] = ch;
}

Useless::Useless(const Useless & f): n(f.n) 
{
    ++ct;
    pc = new char[n];
    for (int i = 0; i < n; i++)
        pc[i] = f.pc[i];
}

Useless::Useless(Useless && f): n(f.n) 
{
    ++ct;
    pc = f.pc;       // steal address
    f.pc = nullptr;  // give old object nothing in return
    f.n = 0;
}

Useless::~Useless()
{
    delete [] pc;
}

Useless & Useless::operator=(const Useless & f)  // copy assignment
{
    std::cout << "copy assignment operator called:\n";
    if (this == &f)
        return *this;
    delete [] pc;
    n = f.n;
    pc = new char[n];
    for (int i = 0; i < n; i++)
        pc[i] = f.pc[i];
    return *this;
}

Useless & Useless::operator=(Useless && f)       // move assignment
{
    std::cout << "move assignment operator called:\n";
    if (this == &f)
        return *this;
    delete [] pc;
    n = f.n;
    pc = f.pc;
    f.n = 0;
    f.pc = nullptr;
    return *this;
}

Useless Useless::operator+(const Useless & f)const
{
    Useless temp = Useless(n + f.n);
    for (int i = 0; i < n; i++)
        temp.pc[i] = pc[i];
    for (int i = n; i < temp.n; i++)
        temp.pc[i] = f.pc[i - n];
    return temp;
}

void Useless::ShowObject() const
{ 
    std::cout << "Number of elements: " << n;
    std::cout << " Data address: " << (void *) pc << std::endl;
}

void Useless::ShowData() const
{
    if (n == 0)
        std::cout << "(object empty)";
    else
        for (int i = 0; i < n; i++)
            std::cout << pc[i];
    std::cout << std::endl;
}

// application
int main()
{
    using std::cout;
    {
        Useless one(10, 'x');
        Useless two = one +one;   // calls move constructor
        cout << "object one: ";
        one.ShowData();
        cout << "object two: ";
        two.ShowData();
        Useless three, four;
        cout << "three = one\n";
        three = one;              // automatic copy assignment
        cout << "now object three = ";
        three.ShowData();
        cout << "and object one = ";
        one.ShowData();
        cout << "four = one + two\n";
        four = one + two;         // automatic move assignment
        cout << "now object four = ";
        four.ShowData();
        cout << "four = move(one)\n";
        four = std::move(one);    // forced move assignment
        cout << "now object four = ";
        four.ShowData();
        cout << "and object one = ";
        one.ShowData();
    }
     std::cin.get();
}