In c# how to pass parameters while calling function when parameter is pointer to pointer

Question

as my function has parameters say---- function(char **p , int*a ,  uint f);
This function is actually present in my unmanaged DLL,while calling the function and passing parameters while calling function from main are
say static unsafe  void Main()
{
  char a='s';
  int b=0;
  uint ulFlags=0;
 
  function(&a, &b, 0);
}but i get error as
Error  1 :--   The best overloaded method match for 'ConsoleApplication2.Program.XRay_SearchDevices(char**, int*, uint)' has some invalid arguments.
Error  2 :--   Argument '1': cannot convert from 'char*' to 'char**'.