return reference or not

[Viet Le Hong]

Should I return reference to a temporaty object in a function. I think I
should but g++ 3.2 always warns this thing.

Eg
..
A& test(A &a, A &aa)
{
A res;
.........
.... doing some thing....

return res;
}


Viet

[Jakob Bieling]

Re: return reference or not

"Viet Le Hong" <lhviet@iprimus .com.au> wrote in message
news:3f6d6d1a$1 _1@news.iprimus .com.au...[color=blue]
> Should I return reference to a temporaty object in a function. I think I
> should but g++ 3.2 always warns this thing.[/color]

Why do you think you should?
[color=blue]
> Eg
> .
> A& test(A &a, A &aa)
> {
> A res;
> .........
> .... doing some thing....
>
> return res;[/color]

Here the object 'res' will be destroyed, so the reference is invalid.
That is why it is not allowed. And yes, g++ 3.2 is right.
[color=blue]
> }[/color]

hth
--
jb

(replace y with x if you want to reply by e-mail)

[WW]

Re: return reference or not

Jakob Bieling wrote:[color=blue]
> "Viet Le Hong" <lhviet@iprimus .com.au> wrote in message
> news:3f6d6d1a$1 _1@news.iprimus .com.au...[color=green]
>> Should I return reference to a temporaty object in a function. I
>> think I should but g++ 3.2 always warns this thing.[/color]
>
> Why do you think you should?
>[color=green]
>> Eg
>> .
>> A& test(A &a, A &aa)
>> {
>> A res;
>> .........
>> .... doing some thing....
>>
>> return res;[/color]
>
> Here the object 'res' will be destroyed, so the reference is
> invalid. That is why it is not allowed. And yes, g++ 3.2 is right.[/color]

Calrification: Actually it is allowed, "only" results in undefined behavior.
g++ is very nice and warns about things like this but not all:

char const *getC() {
std::string x;
// add something to x
return x.c_str();
}

Same thing in another form, but g++ has already no way to detect this.

--
WW aka Attila

[WW]

Re: return reference or not

WW wrote:[color=blue]
> Calrification[/color]

Khm. Clarification it is.

--
WW aka Attila

[jeffc]

Re: return reference or not


"Viet Le Hong" <lhviet@iprimus .com.au> wrote in message
news:3f6d6d1a$1 _1@news.iprimus .com.au...[color=blue]
> Should I return reference to a temporaty object in a function. I think I
> should ...[/color]

What makes you think you "should"?

[Niklas Borson]

Re: return reference or not

"jeffc" <nobody@nowhere .com> wrote in message news:<3f6f07f5_ 3@news1.prserv. net>...[color=blue]
> "Viet Le Hong" <lhviet@iprimus .com.au> wrote in message
> news:3f6d6d1a$1 _1@news.iprimus .com.au...[color=green]
> > Should I return reference to a temporaty object in a function. I think I
> > should ...[/color]
>
> What makes you think you "should"?[/color]

Should a reference outlive the object it refers to?

The answer to your question is the same as the answer to the
above question.