CODEWITHSUNDEEP
c++arraysclass
Medical physicist
Medical physicist

Reputation: 2594

Using the members of a class

I need to use the GNU-GSL interpolation function, that looks like this:

double gsl_interp_eval (const gsl_interp * interp, const double xa[], const double ya[], double x, gsl_interp_accel * acc)

But the xa[] and ya[] arrays that I need are the elements A.x and A.y.value described by these objects:

class c_ys {
  double value;
};

struct s_points {
  double x; 
  c_ys  y;
};

class c_curves {
  vector<s_points> A;
};

How can I use these elements as second and third arguments in the function gsl_interp_eval?

Upvotes: 1

Views: 71

Answers (1)

Sergey Kalinichenko
Sergey Kalinichenko

Reputation: 726479

You wouldn't be able to do it without making copies, because the offsets in memory between the double members is not correct.

Here is how you can do it:

double *x = new double[A.size()];
double *y = new double[A.size()];
for (int i = 0 ; i != A.size() ; i++) {
    x[i] = A[i].x;
    y[i] = A[i].y.value;
}
gsl_interp_eval(...); // call your function
delete[] x;
delete[] y;

Upvotes: 2

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