setTimeout like functionality for c++

Question

I would love create javascript's setTimeout and setInterval like functionality for c++ (without boost). What I would like to achieve: A base class which could call its sub-classed member variables at a repeated or after a single delay.

I have an update function already and time elapsed functionality. I have also found how to pass a member function pointer to the base class and trigger that function using:

class BaseClass {
public:
     template <class object>
     void triggerNow(object *obj, void (object::*func)()) {
          ((obj)->*(func))();
     }

} 

class SubClass : public BaseClass {
public:
    void update() {
         triggerNow(this, &SubClass::worked)
    }
    void worked() {
         cout << "worked!";
    }
}

The problem I currently face is how to store object *obj and void (object::*func)() in a vector (or other container). I am only just figuring out templates...

How can I store the two templated parameters of triggerNow in a vector? Once I can figure this out, I can create my setTimeout and setInterval!

You can declare an std::vector<void (object::*)()> theVector instance variable, then have a look at how Foundation's legendary NSTimer class does the thing (though that is Objective-C, the C parts will match :) — user529758
– user529758, Commented Oct 13, 2012 at 18:28
@Ross: how hard are your timer requirements ? do you expect to be able to do something else in the mean time ? (ie, multi-threading at play...) — Matthieu M.
– Matthieu M., Commented Oct 13, 2012 at 19:29

Geoff Montee · Accepted Answer · 2012-10-13 18:33:31Z

2

No comment on the timing functionality yet.

However, since you are using parent and base classes, I would suggest using polymorphism, rather than a template member function.

class BaseClass {
    public:
        virtual void triggerMe() = 0;

 };

class SubClass1 : public BaseClass {
    public:
        virtual void triggerMe()
        {
            //real code, do something
        }

 };

class SubClass2 : public BaseClass {
    public:
        virtual void triggerMe()
        {
            //real code, do something else
        }

 };

Then you can just have a vector of pointers to BaseClass:

vector<BaseClass*> objects;

objects.push_back(new SubClass1);
objects.push_back(new SubClass2);

for (auto it = objects.begin(); it != objects.end(); it++)
{
    it->triggerMe();
}

answered Oct 13, 2012 at 18:33

Geoff Montee

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1 Comment

Ross Over a year ago

Thanks for your answer. But, correct me if I am wrong, this would have little advantage over BaseClass having virtual void triggerMe()=0?

mauve · Accepted Answer · 2012-10-14 13:29:37Z

1

In order to store object* and object::*func in a vector you can do it like this:

struct Callable
{
  virtual ~Callable () {};
  virtual void operator()() = 0;
};

template <class Object>
struct TemplateCallable : public Callable
{
  typedef void (Object::*MemberFunction)();

  TemplateCallable(Object* obj, MemberFunction mem_fun)
     : _object(obj),
       _mem_fun(mem_fun)
  {}

  void operator() ()
  {
    _object->*_mem_fun();
  }

  Object* _obj;
  MemberFunction _mem_fun;
};

Now you can store them as Callable's in a std::vector, because the templated version is derived from Callable. If you store pointers in a std::vector<> though you need to remember to delete them at some point.

So will get something like this:

class TimerSomething
{
   template <class Object>
   void registerCallback (Object* obj, void (Object::*MemFun)())
   {
     _callbacks.push_back(new TemplatedCallback<Object>(obj, mem_fun));
   }

   void triggerAll ()
   {
     for (std::vector<Callable*>::iterator iter = _callbacks.begin();
          iter != _callbacks.end(); ++iter)
     {
       (**iter)();
     }
   }

   std::vector<Callable*> _callbacks;
};

edited Oct 14, 2012 at 13:29

answered Oct 13, 2012 at 18:36

mauve

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4 Comments

mauve Over a year ago

@MatthieuM. indeed std::function or boost::function really helps. One ends up writing a lot of code when neither boost nor C++11 is available :)

Ross Over a year ago

Thanks will try this! Yes, boost or C++11 would help, but I am looking for a/the vanilla c++ solution.

Ross Over a year ago

virtual void operator() = 0; has a compile time error of 'operator()' cannot be the name of a variable or data member, but I added (for want of a better name) virtual void doIt()=0. Brilliant, thanks!

mauve Over a year ago

@Ross that is because the call operator should actually be virtual void operator() () = 0, I forgot one pair of braces, will fix now.

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