Clang AST visitor, avoid traversing include files

Hello I am trying to implement an AST Clang visitor and this is my code.

class ExampleVisitor : public RecursiveASTVisitor<ExampleVisitor> {
private:
    ASTContext *astContext; // used for getting additional AST info

public:
    virtual bool VisitVarDecl(VarDecl *var) 
    {
        numVariables++;
        string varName = var->getQualifiedNameAsString();
        string varType = var->getType().getAsString();
        cout << "Found variable declaration: " << varName << " of type " << varType << "n";
        APIs << varType << ", ";
        return true;
    }

    virtual bool VisitFunctionDecl(FunctionDecl *func)
    {
        numFunctions++;
        string funcName = func->getNameInfo().getName().getAsString();
        string funcType = func->getResultType().getAsString();
        cout << "Found function declaration: " << funcName << " of type " << funcType << "n";
        APIs << "nn" << funcName <<": ";
        APIs << funcType << ", ";
        return true;
    }

    virtual bool VisitStmt(Stmt *st) 
    {
        if (CallExpr *call = dyn_cast<CallExpr>(st)) 
        {
            numFuncCalls++;
            FunctionDecl *func_decl = call->getDirectCallee();
            string funcCall = func_decl->getNameInfo().getName().getAsString();
            cout << "Found function call: " << funcCall << " with arguments ";
            APIs << funcCall << ", ";
            for(int i=0, j = call->getNumArgs(); i<j; i++)
            {
                string TypeS;
                raw_string_ostream s(TypeS);
                call->getArg(i)->printPretty(s, 0, Policy);
                cout<< s.str() << ", ";
                APIs<< s.str() << ", ";
           }
            cout << "n";
        }
        return true;
    }
};

How can I avoid traversing the included header files, but without loosing their information. I just dont want to print any information about this files but I want clang to know about these files

Thank you