Thread: [Dev-C++] undefined reference to ...

Anyone know why this doesn't work... I cut the problem to this simple
form, only one source file (main.cpp).  I'm getting an undefined
reference to foo::m_instance.  If m_instance were not defined as static
all would be ok.

I'm using Dev-cpp ver 4.9.8.3

Help appreciated...


#include <iostream>
#include <stdlib.h>

using namespace std;

class foo {
private:
  static foo* m_instance;
public:
  static foo* Instance();
};

foo* foo::Instance()
{
  if (m_instance == NULL) 
    m_instance = new foo;
  return m_instance;
}


int main(int argc, char *argv[])
{
  
  system("PAUSE");	
  return 0;
}
-- 
Philippe Parent 
Programmer Analyst 
Integrated Technology Services 
University of New Brunswick 
PO Box 4400 
Fredericton, NB, Canada, E3B 5A3 
Phone (506) 453 3563 
Fax (506) 453 3590

Philippe Parent wrote:

> class foo {
> private:
>   static foo* m_instance;
     ^^^^^^^^^^^^^^^^^^^^^^^
this is only declaration, you have to define it also somewhere, e.g.:

class foo {
    static foo* m_instance;  // declaration
};
foo* foo::m_instance = 0;   // definition