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    <p>If you make it a global object, then everyone has access to it, and anyone can use it without calling <code>getInstance()</code>. If so, then what is the purpose of <code>getInstance()</code> then? First time, you will call it to create the instance, then you wouldn't be required to call <code>getInstance()</code>, since after the first call, you can directly use <code>instance</code>.</p> <p>A <code>private</code> <em>static</em> instance gives you more control how it can be accessed: only through by calling <code>getInstance()</code>. </p> <p>Now why you get <code>multiple definition of instance</code> error when compiling your code? Its because you've defined the global object in the header file itself, which is included in multiple <code>.cpp</code> files. This causes multiple definitions of the object, one definition in each translation unit (.<code>obj</code> file).</p> <p>What you actually should be doing is this:</p> <pre><code>//Singleton.h class Singleton { private : Singleton(); Singleton(const Singleton &amp;); ~Singleton(); static Singleton* instance; //declaration of static member! public: static Singleton* getInstance(); //.. }; </code></pre> <p>And then define the <code>static</code> member in the <code>.cpp</code> file as:</p> <pre><code>//Singleton.cpp Singleton *Singleton::instance = 0; //definition should go in .cpp file! Singleton::Singleton() {} Singleton* Singleton::getInstance() { if ( instance == 0 ) instance = new Singleton(); return instance; } //... </code></pre>
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    1. COI agree with your point. I am just asking why is it giving compilation error on including global object inside a static function...
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