Function pointer trouble

Question

I have a simple code

class a{ public: double (a::*fun)(const double &) const; // .... // }; class b{ public: a c1; double f(const double & x) const{ return 0; } b(){ c1.fun = f; } };

It mean class "a" must work with functions of a certain type, and his work does not depend of this function realization (for example algebraic interpolation). I want make parameter of class - function. But I have some problem. Compiler write

a value of type "int (b::)(const int &x) const" cannot be assigned to an entity of type "int (a::)(const int &) const"

How it's made correct?

Karthik Kalyanasundaram · Accepted Answer · 2014-03-02 14:53:32Z

double (a::*fun)(const double &) const declares a pointer to a member function of class a which return double and takes in const double&.

In your example you are trying to assign the function defined in class b. that's why you get the error.

Kerrek SB · Accepted Answer · 2014-03-02 15:13:33Z

Perhaps a template would solve this:

template <typename T> struct Params { double (T::* fun)(const double &) const; // ... }; class B { Params<B> params; double f(const double &) const; public: B() : params(&B::f) { } // ... };

To invoke the function somewhere in a non-static member function of B on the current instance you would say:

double d; (this->*params.fun)(d);

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