Re: [Boost-users] shared_ptr Initial Assignment

From: Spam-Receiver (spam-receiver_at_[hidden])
Date: 2008-04-25 03:21:30

Hi Lex!

shared_ptr<Foo> bla;                          // Creates an empty shared_ptr
object
bla = shared_ptr<Foo>(new Foo(fooInstance));  // Creates a temporary
shared_ptr object, 
                                              // which owns the copy of
fooInstance,
                                              // then assigns this temporary
object to bla.
                                              // Now both bla and the
temporary object own
                                              // the fooInstance-copy.
...;                                          // Afterwards the temporary
shared_ptr object
                                              // is not needed anymore and
is deleted.
                                              // Now only bla owns the
fooInstance-copy.
                                              // The exact moment, when the
temporary object
                                              // is destroyed, depends on
your compiler toolset.

Regards,
T.

-----Ursprüngliche Nachricht-----
Von: boost-users-bounces_at_[hidden]
[mailto:boost-users-bounces_at_[hidden]] Im Auftrag von Lex Fridman
Gesendet: Freitag, 25. April 2008 04:25
An: boost-users_at_[hidden]
Betreff: Re: [Boost-users] shared_ptr Initial Assignment

Hi Richard,

That was foolish of me to think that bla will point to fooInstance. 
Obviously it will point to a copy of Foo instance. Thanks for that note.

However, you also mentioned that the two options are different:
(1) shared_ptr<Foo> bla(new Foo(fooInstance));

(2) 
shared_ptr<Foo> bla;
bla = shared_ptr<Foo>(new Foo(fooInstance));

You mentioned that the second will create a temporary that will "go 
away". Can you elaborate on that. It seems to me that it shouldn't go 
away, as long as bla is within scope. I guess that was my main question 
originally, whether the second option is a correct way to set bla (when, 
say, it's a class member).

Many thanks!
Lex

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