c++ - Undefined reference Linker error to a variable already in the same file -

I am making the code for linked lists and when I try to compile with G ++, Getting a strange error.

  /cygdrive/c/Users/Blas/AppData/Local/Temp/ccEcixjp.o: In function `node ': /cygdrive/c/Users/Blas/Documents/blas.borde/ Trunk / cs170 / lab6 / list.h: 50: 'CS170 :: ListLab :: node :: node_elive' /cygdrive/c/Users/Blas/Documents/blas.borde/trunk/Cs170/Lab6/List.h Undefined Reference: 50: 'undefined reference to' CS170 :: ListLab :: node :: node_elive '/cygdrive/c/Users/Blas/Documents/blas.borde/trunk/Cs170/Lab6/List.h.5 Undefined reference:: ListLab :: ~ Node :: nodes_alive ' 

And this is my code

  named place CS 170 {namespace listlab {struct node { Int number; // data part node * next; // Fixed int node_live for the next node in the indicator list; // The number of nodes is still / around / non-default constructor node (int value) {number = value; Next = 0; Nodes_alive ++; // a node was created} // destroyer ~ node () {nodes_alive--; // one node was destroyed}}; The strange thing is that I'm already defining node_alive, so I do not know that the linker says that the variable is not defined. Perhaps something is clear that I am missing. Please, I need help.   
 
 
 It seems that you have only declared static data member node_live in class definition, it is defined outside of orbit In some modules in the global namespace  
  int CS170 :: ListLab :: Node :: nodes_alive;  
 
 or 
 
  Namespace CS 170 {Namespace list label {int node :: node_alive; }}  
 
 Although it will be initially initialized from zero, you can explicitly specify as the initiator in your definition.