C ++ - object-oriented (IX)

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Friend

• Friend and friend functions including friend class
• If the function A (non-member function) declared as class C of friend function, then the function A can directly access all the members of the class C object
• If the class is declared as a friend class A class C, so all members of the class A functions have direct access to all members of the class C object
• Friends violate encapsulation of object-oriented, but in some places frequently visited member variables can improve performance

#include <iostream>
using namespace std;

class Point {
	// friend Point add(const Point &, const Point &);
	friend class Math;
private:
	int m_x;
	int m_y;
public:
	int getX() const { return this->m_x; };
	int getY() const { return this->m_y; };
	Point(int x, int y) :m_x(x), m_y(y) { }
};

class Math {
public:
	Point add(const Point &point1, const Point &point2) {
		return Point(point1.m_x + point2.m_x, point1.m_y + point2.m_y);
	}
};

//Point add(const Point &point1, const Point &point2) {
//	return Point(point1.m_x + point2.m_x, point1.m_y + point2.m_y);
//}

int main() {
	Point point1(10, 20);
	Point point2(20, 30);


	Point point = add(point1, point2);

	cout << endl;

	getchar();
	return 0;
}

Inner classes

• If the class A is defined within the class C, then A class is a class internal (nested classes)
• Features inner class
  • Support public, protected, private rights
  • All members of its functions can be accessed directly outside the class object (vice-versa)
  • Member function directly without the class name, the object name to access static members of its outer class
  • It will not affect the memory layout of the outer class
  • May be defined outside of the outer class from outside the class declaration inside

#include <iostream>
using namespace std;

// Person
class Person {
private:
	static int ms_legs;
	static void other() {

	}
	int m_age;
	void walk() {

	}

	// Car
	class Car {
		int m_price;
	public:
		Car() {
			cout << "Car()" << endl;
		}

		void run() {
			Person person;
			person.m_age = 10;
			person.walk();

			ms_legs = 10;
			other();
		}
	};
public:
	Person() {
		cout << "Person()" << endl;

		Car car;
	}

	
};


int Person::ms_legs = 2;

class Point {
	class Math {
		void test();
	};
};

void Point::Math::test() {

}

int main() {
	cout << sizeof(Person) << endl;
	Person person;

	Person::Car car;

	getchar();
	return 0;
}

Local class

• In a class of functions defined inside, called local class
• Features local class
  • Scope is limited to the internal function resides
  • All its members must be defined within the class, does not allow the definition of static member variables
  • Member functions of local variables can not directly access functions (except static variable)

#include <iostream>
using namespace std;

int g_age = 20;

void test() {
	int age = 10;
	static int s_age = 30;

	// 局部类
	class Person {
	public:
		static void run() {
			g_age = 30;
			s_age = 40;

			cout << "run()" << endl;
		}
	};

	Person person;
	Person::run();
}

int main() {
	test();

	getchar();
	return 0;
}

Type Conversion

• C ++ is proposed using the C ++ style casting substituted C style cast
• C ++, there are four types of conversion specifier: static_cast, dynamic_cast, reinterpret_cast, const_cast