Move Assignment Operator in C++ 11

Last Updated : 26 Aug, 2025

Move assignment is a way to transfer resources (like memory, files, etc) from one object to another without copying them.

Example:

C++ 
#include <iostream>
#include <vector>
// for std::move
#include <utility> 

int main() {
    std::vector<int> a = {1, 2, 3, 4};
    std::vector<int> b;
    // move assignment!
    b = std::move(a);  
    // a is now empty
    std::cout << "a.size() = " << a.size() << "\n";
    // b has the data
    std::cout << "b.size() = " << b.size() << "\n";  
}

Output
a.size() = 0
b.size() = 4

Move Assignment Operator

It is a special function that lets an object take ownership of resources from another object without copying.

User-Defined Move Assignment Operator

The programmer can define the move assignment operator .

Example:

C++ 
#include <iostream>
#include <cstring>

class MyString {
    char* data;

public:
    // Constructor
    MyString(const char* str = "") {
        data = new char[strlen(str) + 1];
        strcpy(data, str);
    }

    // User-defined move assignment operator
    MyString& operator=(MyString&& other) {
        std::cout << "Move assignment called\n";

        if (this != &other) {
            // Free old memory
            delete[] data;
            // Steal the pointer
            data = other.data;
            // Set source to null
            other.data = nullptr; 
        }

        return *this;
    }

    // Destructor
    ~MyString() {
        delete[] data;
    }

    void print() const {
        if (data)
            std::cout << data << "\n";
        else
            std::cout << "[empty]\n";
    }
};
int main() {
    MyString a("Hello");
    MyString b("World");

    b = std::move(a);  

    b.print();  
    a.print();  
}

Output
Move assignment called
Hello
[empty]

Need of Move Assignment Operator

  • Improves performance - Move assignment transfers resource instead of copying them, which is much faster, especially for large objects.
  • Reduces memory usage - It avoids creating unnecessary duplicates in memory by reusing existing resources.
  • Handles temporary objects efficiently - Move assignment allows objects to take ownership of data from temporary values without expensive copying.
Comment

Explore