Question

Can anyone explain why following code won’t compile? At least on g++ 4.2.4.

And more interesting, why it will compile when I cast MEMBER to int?

#include <vector>  class Foo {   public:       static const int MEMBER = 1;   };  int main(){       vector<int> v;       v.push_back( Foo::MEMBER );       // undefined reference to `Foo::MEMBER'     v.push_back( (int) Foo::MEMBER ); // OK       return 0; } 

Answer 1

You need to actually define the static member somewhere (after the class definition). Try this:

class Foo { /* ... */ };  const int Foo::MEMBER;  int main() { /* ... */ } 

That should get rid of the undefined reference.