Move constructor not working with const string

Question

Hi all

Please refer below code :
https://code.sololearn.com/cEyO8r8PktRr/?ref=app

I can see that code works perfectly fine if string s is not declared const... Here , s being non const , I can observe s get deleted and prints nothing where as it print proper value for S2

Issue is in case of string s declared as const... Why move constructor is not giving compile time error? Does move not need non const objects ?

Answer 1

It's because std::string's move constructor does not take a const rvalue.
A move constructor requires the modification of the original object and since that object is const you cannot move so it calls the copy constructor instead.

Answer 2

// C++ program with declaring the

// move constructor

#include <iostream>

#include <vector>

using namespace std;

// Move Class

class Move {

private:

    // Declare the raw pointer as

    // the data member of class

    int* data;

public:

    // Constructor

    Move(int d)

    {

        // Declare object in the heap

        data = new int;

        *data = d;

        cout << "Constructor is called for "

             << d << endl;

    };

    // Copy Constructor

    Move(const Move& source)

        : Move{ *source.data }

    {

        // Copying the data by making

        // deep copy

        cout << "Copy Constructor is called -"

             << "Deep copy for "

             << *source.data

             << endl;

    }

    // Move Constructor

    Move(Move&& source)

        : data{ source.data }

    {

        cout << "Move Constructor for "

             << *source.data << endl;

        source.data = nullptr;

    }