What Is A Move Constructor In Modern C++?
In a modern C++ code editor, there are a number of features which help you learn, master, and remember the various features and functions of the C++ language. One such feature of modern C++ is the move constructor that allows you to move the resources from one object to another without copying them. In this post, we explain what the move constructor is in Modern C++. First, let’s remember what are the classes and objects in C++. What are classes and objects in C++? Classes are defined in C++ using keyword class followed by the name of the class. Classes are the blueprint for the objects, and they are user-defined data types that we can use in our program, and they work as an object constructor. Objects are an instantiation of a class. In C++ programming, most of the commands are associated with classes and objects, along with their attributes and methods. Here is a simple class example below. class Tmyclass { public: std::string str; }; Then we can create our objects with this Type of myclass as shown below: Now, lets see what is move constructor, What is move constructor in modern C++? The move constructor is a constructor that allows you to move the resources from one object to another object without copying them. The move constructor allows you to move the resources from an rvalue object into to an lvalue object. The move constructor is used to move data of one object to the new one, it is a kind of to make a new pointer to the members of an old object and transfers the resources to the heap memory. When you move a member, if the data member is a pointer, you should also set the value of the member of the old object to a NULL value. When you use the move constructor, you don’t use unnecessary data copying in the memory. This allows you to create objects faster. Mostly, if your class/object has a move constructor, you can use other move methods of other features of C++, for example, std::vector, std::array, std::map, etc. For example, you can create a vector with your class type then you can use the push_back() method that runs your move constructor. Here is the most common syntax for the move constructor in C++. class_name ( class_name && ) and this is how you can create a move constructor in a class. class Tx { public: Tx() = default; // Default Constructor Tx(Tx&& other) // A Typical Declaration of a Move Constructor { } } As shown above, if you have a move constructor, you should define a Constructor too, otherwise you will have “No matching constructor for initialization of class” error in compilation. In modern C++, a simple class as below has all five special members (copy constructor, copy assignment, move constructor, move assignment, destructor) If you have any of them you should define all five of them ((Rule of Five) including move constructor too. Is there a simple example of a move constructor in modern C++? Here is a simple example of a move constructor. class Tx { public: std::string str; Tx() // Constructor { } Tx(Tx&& other) noexcept: str( std::move(other.str)) // Move Constructor { } }; We can use move […]
