why compiler gives undefined references on static members???

Hano · 06-25-2002, 09:46 PM

Heya,

Im getting this weirds undefined references at link-time when compiling a class with static members, any one may know why?

class AMRMesh {
...
static int Dim;
...
static AMRMesh* root;
....

then the errors i get from the member functions that access the static members are from the following kind.:

/tmp/ccqH023E.o(.AMRMesh::gnu.linkonce.t.Neighbour(int, int, AMRMesh *(*)(AMRMesh *, int, int))+0x192): undefined reference to `AMRMesh::RootGrid'
/tmp/ccqH023E.o(.AMRMesh::gnu.linkonce.t.Neighbour(int, int, AMRMesh *(*)(AMRMesh *, int, int))+0x1f3): undefined reference to `AMRMesh:: Dim'

... and lot others which refer to either AMRMesh:: Dim or AMRMesh::RootGrid, which are the only two static members of AMRMesh

Its there some kind of restriction on members functions accessing static members?

why god why?

crabboy · 06-25-2002, 10:08 PM

What is the version on your compiler and linker?

Code:

g++ --version
ld -version

Hano · 06-25-2002, 10:11 PM

g++/gcc 2.96

GNU ld 2.11.90.0.8

crabboy · 06-25-2002, 10:21 PM

I tried writing a test program with static members and I had no problems linking. Can you post the smallest example possible where you can get the error?

Hano · 06-25-2002, 10:28 PM

------------------test.h------------------------------
#include <iostream.h>

class test {
public:
int a;
static int b;

test() {};
~test() {};

void STb() {
cout << b << endl;
};
};

-------------test.cpp

#include "test.h"

int main() {

test* inst;
inst = new (test);

inst->a=3;
inst->b=5;
// test::b=5; neither works

test::STb();
// neither inst->STb() changes nothing
};

crabboy · 06-25-2002, 11:14 PM

Static variables must be initialized in file scope:

test.cpp

Code:

#include "test.h"

int test::b = 0;

int main() 
{

   test* inst;
   inst = new (test);

   inst->a=3;
   inst->b=5;
   // test::b=5; neither works

   test::STb();
   // neither inst->STb() changes nothing
};

crabboy · 06-25-2002, 11:16 PM

I also had to change the member function STb to be static to call it without an object. I'm assuming that was just a typo when creating the example.

Hano · 06-25-2002, 11:52 PM

yes, it was a typo because i tried both forms, sorry bout that :^)

... but if a static member has to be intialized outside the class, what happens if i want to make the static variable private? i.e: i want the static variable to be changed/updated/handled/used from the methods implemented by the class, what should i do?

Thx :^)

crabboy · 06-26-2002, 11:12 AM

Initialize it after the class definition.

test.h

Code:

class test 
{
   private: 
      int a;
      static int b;

   public:
      test() {};
      ~test() {};

      void setb( int b1 ) { b = b1; };
      void seta( int a1 ) { a = a1; };

      static void STb() 
      {
         cout << b << endl;
      };
};

int test::b = 0;

test.cpp

Code:

#include "test.h"

int main() 
{

   test* inst;
   inst = new (test);

   inst->seta(3);
   inst->setb(5);
   //test::b=5; error private member 

   test::STb();
   // neither inst->STb() changes nothing
}