variable has internal linkage but is not defined
c++, linkage
Solution
Just define it. After the class definition but before the end of the anonymous namespace add this line:
DenseMap<Function*, DenseMap<Instruction*,Invariant*> > Invariant::Invariants;
This will create the static member in every translation unit that includes this header (that's okay because it's in the anonymous namespace, which is unique to each translation unit). That's probably not what you want, but that follows from defining `Invariant` in an anonymous namespace. If you use a named namespace instead, you can put the definition of `Invariants` into a source file and have only one object shared by all the code.
Problem
I have this .h file: ``` namespace{ class Invariant{ public: Invariant(z3::expr e,Instruction *i):Expr(e),I(i){ DenseMap<Instruction*,Invariant*> FunMap = Invariants[F]; } private: //static map static DenseMap<Function*, DenseMap<Instruction*,Invariant*> >Invariants; }; }//end of anonymous namespace ``` When I compile clang says: ``` Invariant.h:46:65: warning: variable '<anonymous namespace>::Invariant::Invariants' has internal linkage but is not defined static DenseMap<Function*, DenseMap<Instruction*,Invariant*> >Invariants; ^ Invariant.h:26:48: note: used here DenseMap<Instruction*,Invariant*> FunMap = Invariants[F]; ``` What's the problem here?