Question

Ran into a bit of an issue with std::bind when adding a placeholder
My code is kind of big so I’ll just stick to the essentials

#define GETFUNC(a) (std::bind(&app::a, this, std::placeholders::_1))
class button{
button(<other parameters here>, std::function<void(int)>) { ... }
..
std::function<void(int)> onhover;
..
};

class app{
app(){
elements.push_back(buttonPtr( new button(<other parameters>, GETFUNC(onHover) );
..
typedef std::unique_ptr<button> buttonPtr;
std::vector<buttonPtr> elements;
..
void onHover(int i) {}
}

That bit of code fails at std::bind ( that much I got from the error log )
but works if I change:

• all std::function<void(int)> to std::function<void()>
• onHover(int i) to onHover()
• std::bind(&app::a, this, std::placeholders::_1) to std::bind(&app::a, this)

Any thoughts on why this happens and how can I fix it?

Answer 1

It’s working fine. Check this and look for differences to your code.

#include <functional>
#include <iostream>


struct app
{
  std::function<void (int)>
  get_func ()
  {
    return std::bind (&app::on_hover, this, std::placeholders::_1);
  }

  void on_hover (int v)
  {
    std::cout << "it works: " << v << std::endl;
  }
};

int
main ()
{
  app a;

  auto f = a.get_func ();
  f (5);
}