Question

I need to implement a structure (or class) where each instance has a “pointer” to a specific function. Is this possible?

Something like this:

struct constrain{

  string                              name;
  int                            direction;
  double evaluate (vector <double> &x_var);
};

Where evaluate “points” to a specific function, so that when I create my constrain object I can tell to which function the object method evaluate should point to and when I later use it (e.g. my constrain objects will be contained within a std::vector) I can call the specific function.

Answer 1

Consider using std::function:

struct Foo
{
    std::function<double (std::vector<double>)> func;
};

It’s better to pass vector by reference as pmr suggested. Here is the full example:

#include <iostream>
#include <vector>
#include <functional>

struct Foo
{
    std::function<double (const std::vector<double> &)> func;
};

static double calc(const std::vector<double> &params)
{
    return 10.0;
}

int main()
{
    Foo f;
    f.func = calc;

    std::vector<double> v;
    std::cout << f.func(v) << std::endl;

    return 0;
}

If your STL implementation does not have std::function consider using boost::function