C++ Function Pointer as Argument - c++

Question

I have tried multiple google searches and help guides, but I'm out of ideas on this one. I have a function pointer that I am using as an argument for another function. Both functions are within the same class. However, I keep getting type conversion errors. I'm sure this is just a syntax problem, but I can't understand what the correct syntax is. Here is a simplified version of my code:
Header File
#ifndef T_H
#define T_H
#include <iostream>
#include <complex>
namespace test
{
class T
{
public:
T();
double Sum(std::complex<double> (*arg1)(void), int from, int to);
int i;
std::complex<double> func();
void run();
};
}
#endif // T_H
Source File
#include "t.h"
using namespace test;
using namespace std;
//-----------------------------------------------------------------------
T::T()
{
}
//-----------------------------------------------------------------------
double T::Sum(complex<double>(*arg1)(void), int from, int to)
{
complex<double> out(0,0);
for (i = from; i <= to; i++)
{
out += arg1();
cout << "i = " << i << ", out = " << out.real() << endl;
}
return out.real();
}
//-----------------------------------------------------------------------
std::complex<double> T::func(){
complex<double> out(i,0);
return out;
}
//-----------------------------------------------------------------------
void T::run()
{
Sum(&test::T::func, 0, 10);
}
Whenever I try to compile, I get the following error:
no matching function for call to 'test::T::Sum(std::complex<double> (test::T::*)(),int,int)'
note: no known conversion for argument 1 from 'std::complex<double> (test::T::*)()' to 'std::complex<double>(*)()'
Any advice appreciated. Or at least a link to a thorough site on how to use function pointers. I am using Qt Creator 2.6.2, compiling with GCC.

Answer 1

Your Sum function expects pointer to a function. And then you try to call it with a pointer to a member function. Learn about pointers to members.

Answer 2

The code itself is a bit messy, I'll only correct the grammer to make it work.
firstly, you shall change the function prototype from
double Sum(std::complex<double> (*arg1)(void), int from, int to);
to
double Sum(std::complex<double> (T::*arg1)(void), int from, int to);
Meaning that it is a pointer to class T's member.
Then, when calling the function, you cant just arg1(),
for (i = from; i <= to; i++)
{
out += arg1();
cout << "i = " << i << ", out = " << out.real() << endl;
}
you have to use (this->*arg1)();
for (i = from; i <= to; i++)
{
out += (this->*arg1)();
cout << "i = " << i << ", out = " << out.real() << endl;
}

Answer 3

How to pass functions as arguments in C++? In general, use a template, unless you have very compelling reasons not do it.
template<typename Func>
void f(Func func) {
func(); // call
}
On the call side, you can now throw in a certain amount of objects (not just pointers to functions):
Functors;
struct MyFunc {
void operator()() const {
// do stuff
}
};
// use:
f(MyFunc());
Plain functions:
void foo() {}
// use
f(&foo) {}
Member functions:
struct X {
void foo() {}
};
// call foo on x
#include <functional>
X x;
func(std::bind(&X::foo, x));
Lambdas:
func([](){});
If you really want a compiled function and not a template, use std::function:
void ff(std::function<void(void)> func) {
func();
}