c++ programming:

[T-Wave]

Hi,

when I compile the code below, I get the following error messages:

[linker error] undefined reference to `sample_class::UsingFile'
ld returned 1 exit status
[Build Error]  ["Class] Error 1 


How do I solve this problem? Thanks.

Code: [Select]

class sample_class
{
   
    public:
        sample_class()
        {
            UsingFile = 0;
        }
       
        ~sample_class()
        {
          --UsingFile;
        }
       
        static bool IsFileInUse();
       
               
    private:
        static int UsingFile;
       
};



bool sample_class::IsFileInUse()
{
           if(UsingFile != 0)
           {
              cout << "File in use" << endl << endl;
              return (true);
           }

}


int main(int argc, char *argv[])
{

     
    system("PAUSE");
    return EXIT_SUCCESS;
}