Creating a Singleton Class - C++ Design Pattern

C++ examples for Design Pattern:Singleton

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Description

Creating a Singleton Class

Demo Code

#include <iostream>

using namespace std;

class Singleton {
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   // This is how clients can access the single instance
   static Singleton* getInstance();

   void setValue(int val) {value_ = val;}
   int  getValue()        {return(value_);}

protected:
   int value_;

private:
   static Singleton* inst_;   // The one, single instance
   Singleton() : value_(0) {} // private constructor
   Singleton(const Singleton&);
   Singleton& operator=(const Singleton&);
};

// Define the static Singleton pointer
Singleton* Singleton::inst_ = NULL;

Singleton* Singleton::getInstance() {
   if (inst_ == NULL) {
      inst_ = new Singleton();
   }
   return(inst_);
}

int main() {

   Singleton* p1 = Singleton::getInstance();

   p1->setValue(10);

   Singleton* p2 = Singleton::getInstance();

   cout << "Value = " << p2->getValue() << '\n';
}

Result


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