How to check if a void* pointer can be safely cast to something else?

Question

Let\'s say I have this function, which is part of some gui toolkit:

typedef struct _My_Struct My_Struct;
/* struct ... */

void paint_handler( void* data )
{         


        

Answer 1

The best you could do would be to look at what data points to to see if it has telltale signs of being what you want, although a) it wouldn't be anywhere close to a guarantee and b) might be dangerous, as you don't know how big the thing data actually points to is. I suppose it isn't any more dangerous than just casting it and using it, but (as has been suggested) a redesign would be better.