"void* is not a pointer-to-object type"

I'm trying to write a program in which a knob drawn in an OpenGL window functions as a GUI widget. Here's the class for the knob:

Code:

class gluisKnob
{
public:
	double value, max, min, default, step, scrollStep;
	
	void setTarget (void*);
};
//  Function to set the target
void gluisKnob::setTarget (void * TARGET)
{
	target = TARGET;
}

There are more functions and members, but this is the important bit.

The knob is to turn when clicked and dragged, or when scrolled on, and changes the value of a variable that target points to.

I have no trouble assigning the address of some other variable (int, float, whatever) to target but how do I use that to assign a value to the variable it points to?

example:

Code:

gluisKnob knob;
double pitch;
knob.setTarget (&pitch);
...
//  This part is during the program's main loop
if (user_clicks_and_drags_the_knob() )
{
    knob.target = knob's_new_value;  // This doesn't work
    *knob.target = knob's_new_value;  // This gives the error message in the thread title
    knob.*target = knob's_new_value  // This doesn't work either.
}

Thanks,
Chris

what is target defined as?

the '.' takes precedence over the '*'. So your problem is that you are trying to call a member function, value from a pointer. There are two ways to overcome this, the first is with parenthesis (*object).function(); The second is the shorthand version, object->function(); Take your pick as they are exactly the same.

(edit)Woops, guess I misread. You need to dereferance target, but since target is a void pointer, it doesn't make sense to just dereferance that. Instead, cast it first the the object pointer you want, then dereferance it. IE *((item*)thing.target) = target.

However, I would rather make a setter and getter for target then take this approach.

Originally Posted by Cogman

(edit)Woops, guess I misread. You need to dereferance target, but since target is a void pointer, it doesn't make sense to just dereferance that. Instead, cast it first the the object pointer you want, then dereferance it. IE *((item*)thing.target) = target.

Better yet, if you can, use a template class.