Userinput mapping?

Hi... In a game I trying to create in C(++), I have spotted a little problem... Thaught I build a class that will handle all the userinput stuff, such as checking keyboard presses, and if pressed call a function. So I made myself a UserInput class that does this thing, it works great with functions that are global but when I was gonna call functions from an Instance of another class (Wich got its life about the same time the userinput class), it didn''t work. But then i realized that the instance of UserInput doesn''t know where that instance is, so I passed that information with the rest... Kind of worked but not exactly as I wanted, now I need a new instance of UserInput for every class that has a function that will be called when a user presses a key. That is kind of annoying because I lost the whole idea of having an Instance of a class to do all the work... So the question I have, Is there any way to make the Userinput without using some instance (I still need one, I know) of it or overload of functions, wich right now looks like the best way to solve the problem? The second question is this: Is this a good way of handling the userinput or is there any other ways? Hope you got the point of my problem and that someone has a idea of solving the problem... If you don''''t want to learn anything you are in really bad trouble...