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What is the best way to declare a global variable?

In C ++, say you want to declare a global variable that will be used by many. How do you do this?

I usually use declare and define in the cpp file and then use extern in another cpp file (and not in the headers).

I do not like this approach, and I am considering something in this direction:

In the header file:

some_file.h

Class MYGlobalClass
{

};


MyGlobalClass& MyGlobalClassInstance()
{
   static MYGlobalClass instance; 
   return  instance;

}

Edit

Consider the following contexts:

  • can be used in multi-threaded applications
  • namespace pollution
  • Can NOT be single line, as many instances of this can be created

What are your thoughts, suggestions, new ideas?

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8 answers

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+2

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+1

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// MyClass.h
class MyClass { ... };
extern MyClass myGlobalInstance;

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MyClass myGlobalInstance;

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1:

// MyClass.h
class MyClass
{
private:  // or protected, if you want it accessible by subclasses
    static MyClass myGlobalInstance;
};

2:

// MyClass.cpp
void someFunction()
{
    // it global, but only accessible inside this function
    static MyClass myGlobalInstance;
    ...
}

3:

// MyClass.cpp
namespace
{
    MyClass myGlobalInstance;
}

// it now only accessible in this file
+1

extern MyGlobalClass MyGlobalClassInstance;

: > . <

0

singleton?

-1

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