classes.md

title
Classes in C++

Classes

By default, all properties of a class are kept private, therefore not visble outside of the scope.

class Position {
  public:
    int x, y;
};

int main(int argc, const char * argv[]) {
  Position position;
  position.x = 10;
  position.y = 10;
}

We can call functions from classes, once we create an instance of it:

class Person {
  public:
    string getName() {
      return "Max";
    }
};

int main() {
  Person max;
  cout << max.getName() << endl;
  return 0;
}

Static methods

class Person {
  public:
    static void greet(string name) {
      cout << "Hello, " << name << endl;
    }
};

int main() {  
  Person::greet("Max");

  return 0;
}

Instead of writing instance.greet() we now address the name of the class, and call the function directly. Therefore, we no longer need an instance to call this function.
The same works for variables inside the class.

Creating objects

The constructor

The constructor is run when the object is created. By default, there is always a constructor, but the default one does nothing. Let's create a custom constructor:

class Person {
  public:
    Person() {
      cout << "Person object is created" << endl;
    }
};
// ......
Person max; 

Making the class static-only and not allowing creating instances:

class Log {
  private:
    Log();
  public:
    static void greet() {
      cout << "hello" << endl;
    }
};

Now, trying to create an instance of this class will always lead to an error.

The destructor

The destructor is create like the constructor, just with a "~" before the name. In this example, as the function creates the instance, once the function is done and removed from the stack, the object is deleted.

class Log {
  public:
    ~Log() {
      cout << "Object will be deleted" << endl;
    }
};

void createObject() {
  Log logger;
}

int main() {
  createObject()

  return 0;
}

Calling the destructor manually is possible, but not recommended and very rare:

logger.~Log();