Service Advertice and Class Usage

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Hello,

When we try to advertise a service we normally use as shown in ros tutorials:

 ros::ServiceServer service = n.advertiseService("add_two_ints", add);

This is with normal function way.

And if we want to use with class, documentation says use like this:

AddTwo a;
 ros::ServiceServer ss = n.advertiseService("add_two_ints", &AddTwo::add, &a);

Which means we need to initialize an object first.

But suppose I want to use everything related with ros in class and suppose my code is like this:

Comm::Comm()
{
  ros::ServiceServer ss = n.advertiseService("add_two_ints", &write);
  // write() is member of Comm class.
}

In my mind, I should have been use like this, but of course this kind of usage gave me error. Is there any possibility to use service advertise in class as describe. Do I need to initialize the class always?