Question

Possible Duplicate:
static members and LNK error in C++
What does it mean to have an undefined reference to a static member?

I have this class:

class A_GItem  
{
public:        
void create_item();    
private:
  static int static_index;  
}

The create_item function is as simply as:

void create_item() { static_index++; }

When compile (after a clean, trying to solve the problem ) I have :
error LNK2001: unresolved external symbol “private: static int A_GItem::static_index

Any idea ? Thanks

Answer 1

Member static variables require initialization. You are merely declaring your variable in your header, but not defining it:

//A_GItem.h
class A_GItem  
{
public:        
void create_item();    
private:
  static int static_index;  
}

//A_GItem.cpp
int A_GItem::static_index = 0;