#include <cstdlib>
#include <iostream>

int vergleich(const double* x, const double* y)
{
  return *x - *y;
}

int main()
{
  double arr[] = { 1, 2, 3, 4, 5 };
  double gesucht = 2;
  double *ptr;
  ptr = (double*) std::bsearch(&gesucht, arr, 5, sizeof(double), 
                               (int (*)(const void*, const void*)) vergleich);
  if (ptr)
  {
    std::cout << *ptr << '\n';
  }
  else
  {
    std::cout << "nicht gefunden\n";
  }
}