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Steven Cool
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 Posted: Tue Oct 28, 2003 2:14 am Post subject: return references |
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Hello,
A little question about returning references.
I have a method which is returning a reference to a 'Trigger object'.
I call the method like this:
Trigger t = method();
then, I do some changes:
t.setsomething();
t.setsomethingelse();
After this operations, I see that the original object isn't changed.
When I do this:
Trigger& t = method();
t.setsomething();
t.setsomethingelse();
then the object is changed.
Can somebody explain this?
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Josephine Schafer
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| Posted: Tue Oct 28, 2003 5:28 am Post subject: Re: return references |
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"Steven Cool" <stevencool007 (AT) hotmail (DOT) com> wrote
| Quote: | Hello,
A little question about returning references.
I have a method which is returning a reference to a 'Trigger object'.
I call the method like this:
Trigger t = method();
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Here you don't return a reference but a copy of a Trigger object (what method
() has to return).
| Quote: | then, I do some changes:
t.setsomething();
t.setsomethingelse();
After this operations, I see that the original object isn't changed.
When I do this:
Trigger& t = method();
t.setsomething();
t.setsomethingelse();
then the object is changed.
Can somebody explain this?
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Well that's the way it's supposed to work  .
In the first code snippet you make changes to the copy of a Trigger object.
Changes made to a copy don't reflect in the original object.
In the second code snippet you return a reference to a Trigger object probably
created by method ().
Reference is an alias for an object. So any changes made to a reference get
reflected in the object it refers to also.
Also make sure you don't return reference to a local object.
HTH,
J.Schafer
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Artie Gold
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| Posted: Tue Oct 28, 2003 5:29 am Post subject: Re: return references |
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Steven Cool wrote:
| Quote: | Hello,
A little question about returning references.
I have a method which is returning a reference to a 'Trigger object'.
I call the method like this:
Trigger t = method();
|
Here, you've invoked the copy constructor to create a new automatic
object.
| Quote: |
then, I do some changes:
t.setsomething();
t.setsomethingelse();
After this operations, I see that the original object isn't changed.
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Of course. You've only modified your `local' copy of the object.
| Quote: |
When I do this:
Trigger& t = method();
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Ah, here you've initialized a reference.
| Quote: | t.setsomething();
t.setsomethingelse();
then the object is changed.
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Well, naturally. ;-)
HTH,
--ag
--
Artie Gold -- Austin, Texas
Oh, for the good old days of regular old SPAM.
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Erik Max Francis
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| Posted: Tue Oct 28, 2003 3:32 pm Post subject: Re: return references |
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Steven Cool wrote:
| Quote: | I call the method like this:
Trigger t = method();
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This invokes the copy constructor, which (is likely to) make a copy of
the object.
| Quote: | Trigger& t = method();
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This does not, so t is the same object as that returned by the call.
--
Erik Max Francis && [email]max (AT) alcyone (DOT) com[/email] && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ It's like being on a diving board that you know is too high.
__/ Sade Adu
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