How to use cmath Bessel functions with Mac-CodePudding

So I am using Mac with the developer tools coming from XCode and according to other answers I should compile using something like:

g   --std=c  17  test.cpp -o test

or using clang but I still I am having trouble making the script find the special functions. What else can I try?

Minimum example

#include <cmath>
#include <iostream>

int main(int argc, char *argv[]){
  double x = 0.5;
  double y = std::cyl_bessel_k(2,x);
  std::cout << "x="<<x <<" -> y(x)="<<y <<std::endl;
  return 0;
}

Error

main2.cpp:6:19: error: no member named 'cyl_bessel_k' in namespace 'std'
  double y = std::cyl_bessel_k(2,x);
             ~~~~~^
1 error generated.

clang version 13.0.0

CodePudding user response：

https://en.cppreference.com/w/cpp/numeric/special_functions/cyl_bessel_j says:

Notes

Implementations that do not support C 17, but support ISO 29124:2010, provide this function if __STDCPP_MATH_SPEC_FUNCS__ is defined by the implementation to a value at least 201003L and if the user defines __STDCPP_WANT_MATH_SPEC_FUNCS__ before including any standard library headers.

Implementations that do not support ISO 29124:2010 but support TR 19768:2007 (TR1), provide this function in the header tr1/cmath and namespace std::tr1.

Armed with your compiler version, I checked https://en.cppreference.com/w/cpp/compiler_support/17#C.2B.2B17_library_features and saw that neither Apple clang nor clang 's own stdlib have these functions. Bad news! You'll need to get them e.g. from boost, or by implementing them yourself. The example on https://en.cppreference.com/w/cpp/numeric/special_functions/cyl_bessel_j actually does have an implementation for you.