How to initialize static members?

This is a discussion on How to initialize static members? within the C++ Programming forums, part of the General Programming Boards category; I have to write a class with a static int member but I do not wish to initialize this member ...

  1. #1
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    How to initialize static members?

    I have to write a class with a static int member but I do not wish to initialize this member until I need to use it in one of my functions.


    Let say i have for example:
    private:
    static int x;

    I tried to initialize this by typing "int Classname::x=0; "in my function and it didn't work.

    So how do I do this??

    Thank you!

  2. #2
    End Of Line Hammer's Avatar
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    Code:
    #include <iostream>
    
    
    class X
    {
      private:
      static int i;
    
      public:
      void set(int j) { i = j;}
      int get() {return i;}
    
    };
    
    int X::i;
    
    int main(void)
    {
      X x1, x2;
      x1.set(10);
      x2.set(20);
      std::cout <<"x1: " <<x1.get() <<std::endl;
      std::cout <<"x2: " <<x2.get() <<std::endl;  
      
      return(0);
    }
    
    /* output:
    
    x1: 20
    x2: 20
    
    */
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  3. #3
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    so that initialization is never done within a function but just independently?

    Thank you so much btw!

  4. #4
    C++ Developer XSquared's Avatar
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    What is the purpose of this line: int X::i;
    Naturally I didn't feel inspired enough to read all the links for you, since I already slaved away for long hours under a blistering sun pressing the search button after typing four whole words! - Quzah

    You. Fetch me my copy of the Wall Street Journal. You two, fight to the death - Stewie

  5. #5
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    that line is used to initialize teh static member.

    But i don't see why it is written there

  6. #6
    Registered User jlou's Avatar
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    The static member must be instantiated somewhere. It is only declared inside the class, but must be instantiated once and only once somewhere outside the class. If your class declaration is in a header file, you usually put the instantiation of static variables in the source file. In Hammer's example the variable is not explicitly intialized, although you could initialize it like this:

    int X::i = 20;

  7. #7
    End Of Line Hammer's Avatar
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    >>In Hammer's example the variable is not explicitly intialized
    To clarify, it is implicitly initialised to zero, just like any other static variable, hence I omitted an explicit initialising statement.
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

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