best way to copy an object of class in c++

Question

if i have an object of class c1 suppose its name object1 and i want to make another object of the same class suppose object2 is it better to declare it like this:

c1 object2 = object1;

or use the copy constructor

c1 object2 = c1(object1);

i now that in C# it differs because in the first case it copies the reference of the object and in the second case it creates a new one, but i want to now if it is the same in c++

What did [your C++ book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) say on the topic? Did you **any** research on your own, before asking? — Algirdas Preidžius, Jun 04 '17 at 15:52
@baselman The existence of this question contradicts such statement. Also, you forgot to answer my first question. What did [your C++ book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list) said on this topic? — Algirdas Preidžius, Jun 04 '17 at 15:56
Creating a new instance from an old one will use the copy constructor, regardless of whether the syntax is `T new = old;`, `T new(old);`, or `T new = T(old);`. [Example](http://coliru.stacked-crooked.com/a/4bc779fe0c36ecd4). — Justin Time - Reinstate Monica, Jun 04 '17 at 16:00
because doing a research includes searching in books @AlgirdasPreidžius — basel man, Jun 04 '17 at 16:00
@JustinTime That is technically true but prior to 17 `T new = T(old)` involves a copy and a move. — Nir Friedman, Jun 04 '17 at 16:01
@NirFriedman True. I've noticed that compilers tend to be eager to optimise it into just a copy, though, even prior to that, so I included it. — Justin Time - Reinstate Monica, Jun 04 '17 at 16:09
@baselman Because you, typically, learn from books. And such a basic question, would've been, **definitely** answered there. In addition, you could type _C++ object copying_ into your favorite search engine, and you would've found the answer to this question as well. — Algirdas Preidžius, Jun 04 '17 at 19:36

score 1 · Accepted Answer · answered Jun 04 '17 at 15:52

1

The two forms will do exactely the same thing (copy the object). It makes no difference.

answered Jun 04 '17 at 15:52

Jesper Juhl

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This is not strictly correct, prior to c++17. The first one only calls the copy constructor, the second calls the copy constructor and then the move constructor. – Nir Friedman Jun 04 '17 at 15:59

best way to copy an object of class in c++

1 Answers1