Move Constructor in C++ with example - Cyborg Coding

A move constructor in C++ is a special constructor that is used to create a new object by moving resources from an existing object. The move constructor typically leaves the original object in a valid but unspecified state. Move semantics is a way to optimize the performance of your program by avoiding unnecessary copies and exploiting the resources of the original object to create a new one.

A move constructor is defined with a single parameter, which is an rvalue reference to an object of the same class. For example:

class MyString {

private:

    char* data;

    size_t size;

public:

    MyString(const char* str) {

        size = strlen(str);

        data = new char[size + 1];

        strcpy(data, str);

    }

    MyString(MyString&& other) {

        data = other.data;

        size = other.size;

        other.data = nullptr;

        other.size = 0;

    }

    ~MyString() { delete[] data; }

};

In this example, "MyString" has a constructor that takes a const char* as parameter, and a move constructor that takes an rvalue reference to an object of the same class as its parameter. The move constructor transfers ownership of the resources (data and size) from the other object to the new object and set the other object's resource pointers to null.

MyString myString1("Hello");

MyString myString2 = std::move(myString1);

In this example, myString1 is created with the constructor that takes a const char* as parameter and myString2 is created with the move constructor. The move constructor transfers ownership of the resources (data and size) from myString1 to myString2 and set myString1's resource pointers to null.

It is important to note that move constructors are called when an object is passed as an rvalue, for example when using std::move function. The move constructor is also called when an object is initialized with an rvalue, for example when using the move assignment operator.

In summary, a move constructor in C++ is a special constructor that is used to create a new object by moving resources from an existing object. The move constructor typically leaves the original object in a valid but unspecified state. Move semantics is a way to optimize the performance of your program by avoiding unnecessary copies and exploiting the resources of the original object to create a new one. A move constructor is defined with a single parameter, which is an rvalue reference.