Singleton Design Pattern using C++

Why would we want to use a Singleton? In some programs you would want a single instance of a class, for example a db connection. If you have multiple connections you may have fall into update race proplems or lockups from multiple connections trying to gain access the same db.
An implementation of the singleton pattern must:

• ensure that only one instance of the singleton class ever exists; and
• provide global access to that instance.

Typically, this is done by declaring all constructors of the class to be private; and providing a static method that returns a reference to the instance. We start with createing a 'Singleton' class, a .cpp file.

#include <string>

class Singleton
{
    static Singleton* s;
    std::string onlyOne;
    Singleton();
public:

    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;
    ~Singleton();
    static Singleton* getInstance();
    void setSingleton(const std::string &st);
    std::string getSingelton();
};

You need to disable the copy constructor.
Now let's create the .h Singleton header file.

#include <string>
class Singleton
{
    static Singleton* s;
    std::string onlyOne;
    Singleton();
public:
    Singleton(const Singleton&) = delete;
    Singleton& operator=(const Singleton&) = delete;
    ~Singleton();
    static Singleton* getInstance();
    void setSingleton(const std::string &st);
    std::string getSingelton();
};

Now let's put this all together in main method in the main.cpp file

#include <iostream>
#include "Singleton.h"

using std::cout;
using std::endl;

int main(int argc, char* argv[] ) {

    cout << "The Ray Code is AWESOME!!" << endl;

    cout << "The value is the " << Singleton::getInstance()->getSingelton() << endl;

    Singleton::getInstance()->setSingleton("Changed Value");
    cout <<"The value is the " << Singleton::getInstance()->getSingelton() << endl;

    return 0;
}

Let's compile and run:

The value is the Original Value
The value is the Changed Value

The Ray Code is AWESOME!!!
wikipedia

Find Ray on:

facebook
youtube
The Ray Code
Ray Andrade