Scope of passing function as a parameter

Question

I am having some problems with my code.

I have a class:

class SingleNeuron {

public:

    double hh_function (double t , double u);
    double nn_function (double t , double u);
    double zz_function (double t , double u);
    double VV_function (double t , double u);

    void calculating_next_step( double t0, double dt ) {

        hh=rk4 ( t0, hh, dt, hh_function );
        nn=rk4 ( t0, nn, dt, nn_function );
        zz=rk4 ( t0, zz, dt, zz_function );
        VV=rk4 ( t0, zz, dt, VV_function );

 }

};

/*the rk4 is a function of someone else:*/
double rk4 ( double t0, double u0, double dt, double f ( double t, double u ) );

I'm getting the problem in hh, nn , zz ,VV:

error C3867: 'SingleNeuron::hh_function': function call missing argument list;
use '&SingleNeuron::hh_function' to create a pointer to member

I tried to change it to &SingleNeuron::hh_function and the problem is:

error C2664: 'rk4' : cannot convert parameter 4 from
'double (__thiscall SingleNeuron::* )(double,double)'
to 'double (__cdecl *)(double,double)'
1> There is no context in which this conversion is possible

Answer 1

You can not pass a member function as a function as a function pointer, since a member function is meaningless without an instance.

If your hh_function only depends on its parameters. You can declare it as a static member function. In this way, you can pass it as a normal function pointer.