Question

i’ve just begin to approach in cpp. so mayebe it is a simple problem, mayebe it is a structural problem and i have to change my design.

i have 3 facts and 1 problem.

fact 1:

i have a Gesture class with a vector of Point inside

vector<Point> Gesture::getPoints();

the Gesture instances recive the vector in the constructor so i think it could be normal vector (no pointer). vectors are not shared between gestures neither a gesture change its own points (aside normalization).

fact 2:

Gesture class has a static method that normalize all points between [0:w]. normalize take a memory address to normalize in-place. i think that normalization in place could be a nice thing. this normalization method is used by widgets to visualize the path in vector for normalize point between 0 and width-of-the-widget

static void Gesture::normalize(vectot<Point> &pts, int w);

fact 3:

i have a widget that visualize points:

void MyWidget::setGestures(vector <Gesture *> gs)

because the gesture is produced by another widget dinamically i thought that it has been handy to work with a vector of pointer and can do some new Gesture calls.

problem:

i have several widget that visualize gesture. each one with a different width (== different normalization).

the first time i use:

Gesture::rescale(this->w, this->points);
Gesture * g = new Gesture(getPoints(), centroids);

and it’s everything ok

the second time i have:

vector<Gesture* > gs = foo();
int num_gesture = gs.size();
for (int i = 0; i < num_gesture; ++i) {
    vector<Point> pts = gs.at(i)->getPoints();
    Gesture::rescale( widget->getWidth(), pts );
}
widget->setGestures(gs);

and here there are problem because this widget is drawing not normalized points.

i have tried some crazyness with pointers but if the program does not crash.. anyway it not normalized. and it get some error like: pointer to a temporary.

i don’t knwo what to think, now.

Answer 1

Although your question is a little confusing, the problem seems to be that Gesture::getPoints() returns a vector and not a reference to a vector, so it actually returns a copy to the internal vector, and so changing it does not modify the gesture object itself.