c++ class function as argument to another class function - c++

Question

I am trying to pass a templated member function of one class as an argument of a templated member function of another class. I've seen several examples of using function pointers, but i am trying to pass this function argument directly.
in
template <class Item>
class MinHeap
i have the function
tempmlate <class Item>
template <class Process>
void inorder (Process f, const int index)
{
if (index < size())
{
inorder(f, index*2 +1);
f(data[index]);
inorder(f, index*2 +2);
}
}
and in
template<item>
class sequ
i have a function called
void insert(const Item& x);
I'm trying to do this in main:
MinHeap<int>* tree = new MinHeap<int>();
//insert some stuff
sequ<int>* s = new sequ<int>();
tree->inorder(s->insert);
but the last line gives me the error:
error: reference to non-static member function must be called
tree->inorder(s->insert);
when i replace s->insert with the function, print
void print(int x)
{
printf("%d\n", x);
}
it works fine.
how do i use a member function as argument?

Answer 1

&sequ<int>::insert gives you a pointer to the the member function insert of the sequ<int> class. However, to call a member function you also need an instance of the class. Said another way, you cannot perform f(data[index]); in the inorder function because you need an object instance to call the f member function.
Example Code
#include <iostream>
#include <string>
#include <vector>
template<typename T>
class Bar
{
public:
void barFn(const std::string& data) { std::cout << "Bar<T>::barFn: " << data << "\n"; }
};
template<typename T>
class Foo
{
public:
Foo() : mData{ "Hello World" } {}
template<typename C, typename F>
void fooFn(C* instance, F memFn, size_t n)
{
(instance->*memFn)(mData[n]);
}
private:
std::vector<std::string> mData;
};
int main()
{
Bar<int> bar;
Foo<int> foo;
foo.fooFn(&bar, &Bar<int>::barFn, 0);
return 0;
}
Example Output
Bar<T>::barFn: Hello World
Live Example