There are several reasons for a method beign unable to use a class intance's fields, the most current are that the fields that you try to use doesn't exist (this case) and that the method is not from the class (the one i was talking about).
Take a look at the cpp file you uploaded, line 528:
Code: Select all
bool b2dJson::loadIntoExistingWorld(b2World* world, const char* filename, std::string& errorMsg)