What is the rule of three, five, and zero?

The Rule of Three, Five, and Zero in C++ is a crucial concept in understanding how to manage resources in classes. It primarily deals with resource management, ensuring there are no memory leaks, and defining how objects behave when copied or assigned.

Rule of Three

The Rule of Three states that if a class requires a user-defined destructor, copy constructor, or copy assignment operator, it probably requires all three. This is important for properly managing dynamically allocated memory.

Example of Rule of Three:


        class MyClass {
        private:
            int* data;
        public:
            MyClass(int value) {
                data = new int(value);
            }
            ~MyClass() {
                delete data;
            }
            MyClass(const MyClass& other) {
                data = new int(*other.data);
            }
            MyClass& operator=(const MyClass& other) {
                if (this != &other) {
                    delete data;
                    data = new int(*other.data);
                }
                return *this;
            }
        };

Rule of Five

The Rule of Five extends the Rule of Three by adding the move constructor and move assignment operator. If you define any of the three special member functions, you should also define these two, which help optimize resource management by allowing resources to be transferred rather than copied.

Example of Rule of Five:


        class MyClass {
        private:
            int* data;
        public:
            MyClass(int value) : data(new int(value)) {}

            ~MyClass() {
                delete data;
            }

            MyClass(const MyClass& other) {
                data = new int(*other.data);
            }

            MyClass& operator=(const MyClass& other) {
                if (this != &other) {
                    delete data;
                    data = new int(*other.data);
                }
                return *this;
            }

            MyClass(MyClass&& other) noexcept : data(other.data) {
                other.data = nullptr;
            }

            MyClass& operator=(MyClass&& other) noexcept {
                if (this != &other) {
                    delete data;
                    data = other.data;
                    other.data = nullptr;
                }
                return *this;
            }
        };

Rule of Zero

The Rule of Zero emphasizes that classes should manage their resources by using smart pointers or other resource-managing classes. By relying on these classes, you can avoid dealing with manual memory management altogether.

Example of Rule of Zero:


        #include <memory>

        class MyClass {
        private:
            std::shared_ptr data;
        public:
            MyClass(int value) : data(std::make_shared(value)) {}
            // No manual management needed
        };

What is the rule of three, five, and zero?

Rule of Three

Example of Rule of Three:

Rule of Five

Example of Rule of Five:

Rule of Zero

Example of Rule of Zero:

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What is the rule of three, five, and zero?

Rule of Three

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Rule of Five

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Rule of Zero

Example of Rule of Zero:

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