references to function in classes

Hey,
How can I get this one work?
There is a class which gets a function f as an argument. This function is combined with other ones to a new function diff. So far it's fine.

Now I want to pass this new function as a reference for further usage. I just can't get around this error the compiler gives me: " cannot convert ‘double (test::*)(double)’ to ‘double (*)(double)’ in assignment "

I even don't understand the problem at all.

Code:

//provides a function (diff) which gives the difference from an inputfuntion to zero.
class test
{
public:
  test() {diff = &standardFunc_;};
  ~test();
   double (*diff)(double x);
   void setFunc(double f(double x))
  {
    func_ = f;
    diff = &test::calc_; //error:  cannot convert ‘double (test::*)(double)’ to ‘double (*)(double)’ in assignment 
  };

private:
  static double standardFunc_(double x) { return 0;}
  double (*func_)(double x);
  double calc_(double x)
  {
    return func_(x) - standardFunc_(x);
  }	
};

I need that for ceating an easy-to-use fit-interface for the gsl-library. For fitting I need to give some functions as refrences - but this doesn't work within a class .

Hope somebody can help
Christian

http://www.newty.de/fpt/index.html
Declaring function pointers to class member functions is a bit more involved than what you have at the moment.

thanks, i see... ok, i will read this Tutorial.

Is there anybody who knows and wants to post an example how to use this class-function instead of any global (static) function?

greets
Christian

Thank you for help and suggestions.

I don't want to declare the method static, because it should be different for every object. Anyway, I've found a solution.

For the given example:
I declare a static vector of pointers to methods func_. There every object gets its own entry. Then, instead of using the method diff, I use calc_ with the appropriate method func_.