Design Pattern

Design Pattern in c++

1. Creational Patterns

• 1.1 Singleton
• 1.2 Builder

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1. Creational Patterns

Ceational design patterns are design patterns that deal with object creation mechanisms.

1.1 Singleton

A class of which only a single instance can exist. The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance. It is named after the singleton set, which is defined to be a set containing one element. This is useful when exactly one object is needed to coordinate actions across the system.

Ex:

class SingleTon
{
public:
	static SingleTon* GetObj()
	{
		if (obj == nullptr)
			obj = new SingleTon;
		return obj;
	}
	void print()
	{
		cout << count << endl;
	}
private:
	static SingleTon *obj ;
	static int count;
	SingleTon(){}
};
int SingleTon::count = 0;
SingleTon *SingleTon::obj = nullptr;
int main()
{
	SingleTon *obj;
	obj = SingleTon::GetObj();
	obj->print();
	SingleTon *obj1;
	obj1 = SingleTon::GetObj();
	obj1->print();
	_getch();
	return 0;
}

1.2 Builder Pattern

Separates object construction from its representation. The Builder Pattern is used to separate the construction of a complex object from its representation so that the same construction process can create different objects representations.