cpp file to http://stackoverflow.com/questions/19450198/calling-gsl-function-inside-a-class-in-a-shared-library

MyClass.cpp

#include "MyClass.h"

// Define Class members
// =====================

double MyClass::GetSolution( ) {
		
	// point the pt_MyClass element to this class
	p->pt_MyClass = this;


	// instantiate a gsl_function ...
	gsl_function F;
	F.params   = p;
	// ... and point the address of our
	// wrapper to it
	F.function = &gslClassWrapper;

	std::cout << "at x=2, objective function value is " << gslClassWrapper(2.0,p) << std::endl;
	std::cout << "at x=1, objective function value is " << gslClassWrapper(1.0,p) << std::endl;

	// set up GSL root solver
	const gsl_root_fsolver_type *T;
	gsl_root_fsolver *sroot;
	T     = gsl_root_fsolver_brent;
	sroot = gsl_root_fsolver_alloc (T);

	double low = -5;
	double hi  = 5;
	double root;
	root = find_root(sroot,&F, low , hi );

	return root;
}

double MyClass::getC( void ) { return( p->c); } ; 


// Define Objective Function
// =========================

double MyClass::obj(double x, void * par) {

	gsl_f_pars *p = (gsl_f_pars *)par;
	//return x;
	//return (p->a * x + p->b) * x + p->c;
	return pow(x - p->a , 3); 
}

// main routine
// ============

int main(){
	MyClass C;

	// allocate the param structure
	gsl_f_pars myp;
	myp.a=1.0;
	myp.b= 0;
	myp.c=-5;

	// point to myp from inside the class
	C.setPars( &myp );
	std::cout << "checking value of C: " << C.getC() << std::endl;

	std::cout << "computing result : " << C.GetSolution() << std::endl;

	return 0;
}