CODEWITHSUNDEEP
c++
Brandon
Brandon

Reputation: 23500

Static Variable Undefined Reference

I'm trying to make sure that a module only loads exactly once but when I do it my way, the compiler spits out "Undefined reference to both my static class variables :S

class Text : public Parent
{
    private:
        static int Instances;
        static HMODULE Module;

    public:
        Text();
        Text(Text&& T); 
        Text(std::wstring T); 
        ~Text();

        virtual Text& operator = (Text&& T); 
};

Text::Text() : Parent() {}

Text::~Text()
{
    if (--Instances == 0)
        FreeLibrary(Module); // Only free the module when
                             // no longer in use by any instances.
}

Text::Text(Text&& T) : Parent(std::move(T)), Module(std::move(T.Module))

Text::Text(std::wstring T) : Parent(T)  // Module only loads when
                                        // this constructor is called.
{
    if (++Instances == 1)
    {
        Module = LoadLibrary(_T("Msftedit.dll"));
    }
}

Text& Text::operator = (Text&& T)
{
    Parent::operator = (std::move(T));
    std::swap(T.Module, this->Module);
    return *this;
}

Any ideas why it says undefined reference to BOTH variables (Instances & Module)?

Upvotes: 0

Views: 473

Answers (2)

gongzhitaao
gongzhitaao

Reputation: 6682

You should define your static variable in your before you can use it.

Add

int Text::Instancese = 0 // whatever value you need.

at top of your .cpp file.

Upvotes: 1

Pete Becker
Pete Becker

Reputation: 76235

The class definition declares two static data members, Text::Instances and Text::Module. You also have to define those data members if the code actually uses them. Just like void f(); declares a function, but you can't call it unless you also define it. So add:

int Text::Instances;
HMODULE Text::Module;

to your source code. (This has nothing to do with whether your current code is written entirely in a header or split into header and source; if you use it you have to define it)

Upvotes: 1

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