Question

I have two pointers (const Vec* a and const Vec b)
in a given piece of code, I need to pass these two values​​, which are instantiated during the code, for a function that has no parameter (const Vec *) but only (Vec *).
How could I do this without moving the function definition, but if necessary, what procedure should I take?

//const Vec* from;
//const Vec* at;
Vec* viewVec; 
viewVec = Vec::sub( view->at, view->from);


//static Vec* sub(Vec*, Vec*);
Vec* Vec::sub(Vec* a, Vec* b) {
    return new Vec(a->x - b->x, a->y - b->y, a->z - b->z);
}

Answer 1

You can use const_cast for this, e.g.

viewVec = Vec::sub(const_cast<Vec*>(view->at), const_cast<Vec*>(view->from));

Whether or not you should is another matter. If you really can’t change the signature of the function (which is probably the easiest fix), you can always write a wrapper which contains the dodgy casting – that way, at least the caller doesn’t need to do any casting itself:

Vec *Vec::sub(const Vec *a, const Vec *b) {
    return sub(const_cast<Vec*>(view->at), const_cast<Vec*>(view->from));
}