String ID inside .RC file is not recognized in code

I'm using C++ Builder 11.2 and have a following strings.rc file added to my project:

#define ID_TESTSTRING    1

STRINGTABLE
BEGIN
    ID_TESTSTRING,   "Just for testing"
END

Inside my Form1 (Unit1.cpp) I use the following code:

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    wchar_t resString[100];
    LoadString(HInstance, ID_TESTSTRING, resString, 100); // undeclared identifier ID_TESTSTRING!
    ShowMessage(resString);
}

The problem is that I get this 'undeclared identifier' error. If I replace ID_TESTSTRING with its numeric constant 1 then everything works as expected. Why the identifier is not recognized? Because, I want to work with ID's in my code, not with their numeric constants.

Identifiers are not "exported" automatically, or created as identifiers in all source files.

You need to put the ID_TESTSTRING macro definition in a separate header file, that you include in both your resource and C++ source files.

resources.rh

#define ID_TESTSTRING    1

resources.rc

#include "resources.rh"

STRINGTABLE
BEGIN
    ID_TESTSTRING,   "Just for testing"
END

Unit1.cpp

#include "resources.rh"

void __fastcall TForm1::Button1Click(TObject *Sender)
{
    wchar_t resString[100];
    LoadString(HInstance, ID_TESTSTRING, resString, 100);
    ShowMessage(resString);
}