Get a pointer to object's member function

Question

Here is the problem:

1) I have a class like so:

class some_class
{
public:
    some_type some_value;
    int some_function(double *a, double *b, int c, int d, void *e);
};

2) Inside some_function, I use some_values from some_class object to get a result.

3) So, I have a concrete object and I want to get a pointer to this object some_function.

Is it possible? I can't use some_fcn_ptr because the result of this function depends on the concrete some_value of an object.

How can I get a pointer to some_function of an object? Thanks.

typedef  int (Some_class::*some_fcn_ptr)(double*, double*, int, int, void*);

Answer 1

You cannot, at least it won't be only a pointer to a function.

Member functions are common for all instances of this class. All member functions have the implicit (first) parameter, this. In order to call a member function for a specific instance you need a pointer to this member function and this instance.

class Some_class
{
public:
    void some_function() {}
};

int main()
{
    typedef void (Some_class::*Some_fnc_ptr)();
    Some_fnc_ptr fnc_ptr = &Some_class::some_function;

    Some_class sc;

    (sc.*fnc_ptr)();

    return 0;
}

More info here in C++ FAQ

Using Boost this can look like (C++11 provides similar functionality):

#include <boost/bind.hpp>
#include <boost/function.hpp>

boost::function<void(Some_class*)> fnc_ptr = boost::bind(&Some_class::some_function, _1);
Some_class sc;
fnc_ptr(&sc);

C++11's lambdas:

#include <functional>

Some_class sc;
auto f = [&sc]() { sc.some_function(); };
f();
// or
auto f1 = [](Some_class& sc) { sc.some_function(); };
f1(sc);