C ++中的函数调用问题

Question

I have a problem with my program, I work actually on interpolation with Cubic BSplines, but when I call my interpolate function in main() I get a wrong result, and when I write directly the function in main() it works :(. I can not see what is the difference between the both.

void CubicBSpline::interpolation(){
  Point3d point;
  for(unsigned int i = 3; i < (knots->m_points).size(); i++){
    for(double t=0; t<1; t+=0.1){
      point = bSplineCubicUniform(i, t);
      cout << point.x << " " << point.y <<endl;
    }
  }
}

int main(){
  CubicBSpline cbs(4, 4);
  cbs.interpolation(); //this is the call of my function but I got a wrong result

  // and here I write directly my function and that's work good
  Point3d point;
  for(unsigned int i = 3; i < (cbs.knots->m_points).size(); i++){
    for(double t=0; t<1; t+=0.1){
      point = cbs.bSplineCubicUniform(i, t);
      cout << point.x << " " << point.y <<endl;
    }
  }
  return 0;
}

Answer 1

Your description is decidedly uninformative (and it seems you'd rather respond with abrasive comments than provide more information) so all I can give you is a general answer. A bunch of things could be different between these two cases. Firstly presumably these two functions are defined within different files therefore depending on what's included different types could have entirely different definitions. From what I can see you don't have any scoping problems, but maybe I'm wrong. And also since you don't provide us with code for these other functions who knows what side effects they have.

However honestly I think that your problem most likely is due to an optimization that the compiler makes when the function is inlined. (Try compiling without optimizations).

Finally the most glaringly bad thing here is that you have a loop that uses a double as its iterator... are you kidding me? Who knows how many times that loop get's executed. It's entirely dependent on the compiler's floating point round off, which means not only is it unpredictable, but even if you get lucky and it works on your machine, who knows if it will work on other ones.