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How to write a singleton class in C++?
Singleton design pattern is a software design principle that is used to restrict the instantiation of a class to one object. This is useful when exactly one object is needed to coordinate actions across the system. For example, if you are using a logger, that writes logs to a file, you can use a singleton class to create such a logger. You can create a singleton class using the following code.
Example
#include <iostream> using namespace std; class Singleton { static Singleton *instance; int data; // Private constructor so that no objects can be created. Singleton() { data = 0; } public: static Singleton *getInstance() { if (!instance) instance = new Singleton; return instance; } int getData() { return this -> data; } void setData(int data) { this -> data = data; } }; //Initialize pointer to zero so that it can be initialized in first call to getInstance Singleton *Singleton::instance = 0; int main(){ Singleton *s = s->getInstance(); cout << s->getData() << endl; s->setData(100); cout << s->getData() << endl; return 0; }
Output
0 100
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