Ptr a = CreateObject < Node > ();

Question

While i am going through different examples in NS-3 ( network simulator) i came across a definition like this. I coudn't figure out what exactly this syntax means.

Ptr<Node>  a = CreateObject < Node > ();

In some other cases they use similar syntax, but RHS is quite different.

HelperClass help;

Ptr< xxx > a = help.somethingrandom();

or they prefix const before xxx.

I guess this is a different way of creating objects in c++. But it is still confusing. Can anyone please elaborate whats happening ? Thanks in advance.

have you heard about a concept of [templates](http://stackoverflow.com/documentation/c%2b%2b/460/templates)? — W.F., Nov 08 '16 at 11:28
Learning c++ by reading the code of a very complex system is probably the worst way I can imagine. I suggest you [choose a book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) and go from there. — StoryTeller - Unslander Monica, Nov 08 '16 at 11:40
Thank you. I have some basic idea about c++.( until class and object definitions) So other question is from which topic do you suggest me to start? — spectre, Nov 08 '16 at 11:42
If you have a handy book. And you feel you covered the preliminary material. Read about templates (from your book). To see how c++ programmers use those concepts to come up with interesting techniques, I suggest https://en.wikibooks.org/wiki/More_C%2B%2B_Idioms — StoryTeller - Unslander Monica, Nov 08 '16 at 11:51

StoryTeller - Unslander Monica · Answer 1 · 2016-11-08T12:19:29.557

1

Assuming Ptr is some smart pointer class. It seems CreateObject is template function, with implementation that simply boils down to this:

template<typename Obj>
Ptr<Obj> CreateObject() {
  return Ptr<Obj>(new Obj);
}

The idea is that the code is generic, it will work for any type. Using a function ensures no resources leak during multiple initializations, if a constructor happens to throw an exception.

The standard library has an equivalent std::shared_ptr/std::unique_ptr with matching std::make_shared/std::make_unique functions.

edited Nov 08 '16 at 12:19

answered Nov 08 '16 at 11:35

StoryTeller - Unslander Monica

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Thank you. I am not aware of both smart pointers and template functions. So how can i understand this then? – spectre Nov 08 '16 at 11:38
Hi, i have gone through some basics of template. But didn't come across anything similar to the one that you have mentioned in the answer. Can you please give me a reference ( preferably video link) for that? – spectre Nov 10 '16 at 13:02

Ptr a = CreateObject < Node > ();

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