Serializing a static data member

 Is there any chance I can serialize a static data member ?

 Consider the following case.

 class CB:public CA
 {
   protected:
   static UINT m_number;

..... (more data menbers)


  public:

..... (some functions)

  Serialize (Carchive &ar);

....
 }

The function serialize is defined as follows:

void CB::Serialize(CArchive &ar)
{

   
    if (ar.IsStoring())
              ar <<m_number;
    else
             ar >>m_number;

  CA::Serialize(ar);
}


m_number is used to store the amount of  objects of the same class.

When linking the following error occurs:

rror LNK2001: unresolved external symbol "protected: static unsigned int  CB::m_number" (?m_number@CB@@1IA)


Any help ? thanks.