Compile ok,Excute error,why???

This is a discussion on Compile ok,Excute error,why??? within the C++ Programming forums, part of the General Programming Boards category; Hi, I have a question here Code: #include<iostream> using namespace std; class Counted{ public: Counted():id(count++){ cout << id << endl; ...

  1. #1
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    Compile ok,Excute error,why???

    Hi, I have a question here

    Code:
    #include<iostream>
    using namespace std;
    
    class Counted{
    public:
    	Counted():id(count++){ cout << id << endl; }
    	~Counted();
    private:
    	static int count;
    	int id;
    	
    };
    
    Counted::~Counted()
    {
    	cout << "Being destroyed" << endl;
    }
    
    void main()
    {
    	Counted c;
    }
    When i compile it ,it's OK!
    When i excute it ,the following error message:
    Linking...
    HW_Ch13_1.obj : error LNK2001: unresolved external symbol "private: static int Counted::count" (?count@Counted@@0HA)
    Debug/HW_Ch13_1.exe : fatal error LNK1120: 1 unresolved externals
    Error executing link.exe.

    HW_Ch13_1.exe - 2 error(s), 0 warning(s)

    so, could anyone tell me why??thx~~~

  2. #2
    People Love Me
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    Jan 2003
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    412
    Usually that happens when you declare something in a class but never really define it. ...And... main() should return an int.

  3. #3
    C/C++Newbie Antigloss's Avatar
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    You forgot to initialize "static int count"

  4. #4
    Just Lurking Dave_Sinkula's Avatar
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    Oct 2002
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    5,006
    Quote Originally Posted by Lorin_sz
    When i compile it ,it's OK!
    When i excute it ,the following error message:
    Linking...
    HW_Ch13_1.obj : error LNK2001: unresolved external symbol "private: static int Counted::count" (?count@Counted@@0HA)
    Debug/HW_Ch13_1.exe : fatal error LNK1120: 1 unresolved externals
    Error executing link.exe.

    HW_Ch13_1.exe - 2 error(s), 0 warning(s)
    First, that's not execution, that's linking.

    Second, static data members need to be initialized like this.
    Code:
    #include<iostream>
    using namespace std;
    
    class Counted{
    public:
    	Counted():id(count++){ cout << id << endl; }
    	~Counted();
    private:
    	static int count;
    	int id;
    	
    };
    
    int Counted::count = 0;
    
    Counted::~Counted()
    {
    	cout << "Being destroyed" << endl;
    }
    
    int main()
    {
    	Counted c;
    }
    http://www.parashift.com/c++-faq-lit...html#faq-10.11
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  5. #5
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    thanks all

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