std::vector::assign

what happens memory wise with this scenerio:

std::vector<int> vecInt(20, 999);

VecInt.assign(20, 0);


do all the 999 values get overwritten or does the vector reassign the
memory lso?

thanks

re: std::vector::assign

scooter wrote:[color=blue]
> what happens memory wise with this scenerio:
>
> std::vector<int> vecInt(20, 999);
>
> VecInt.assign(20, 0);[/color]

You have the parameters backwards.
[color=blue]
> do all the 999 values get overwritten or does the vector reassign the
> memory lso?[/color]

Do you want the memory to be freed and reallocated?
If so, I know that

std::vector <int> vecInt (999, 20);

{
std::vector <int> temp ();
temp.swap (vecInt)
}

will do it. IIRC, vector::assign works identically to
constructing a new vector and using operator=, and in
that case (again IIRC) the memory is not guaranteed to
be released and reallocated.

Regards,
Buster.

re: std::vector::assign

Buster Copley wrote:[color=blue]
> scooter wrote:
>[color=green]
>> what happens memory wise with this scenerio:
>>
>> std::vector<int> vecInt(20, 999);
>>
>> VecInt.assign(20, 0);[/color]
>
>
> You have the parameters backwards.[/color]

I'm sorry, I misunderstood the next sentence. You're fine.
[color=blue][color=green]
>> do all the 999 values get overwritten or does the vector reassign the
>> memory lso?[/color][/color]

I think the 999s get overwritten.
[color=blue]
> Regards,
> Buster.[/color]

re: std::vector::assign

On Wed, 17 Sep 2003 20:18:39 +0100, Buster Copley <buster@none.com>
wrote:
[color=blue]
>scooter wrote:[color=green]
>> what happens memory wise with this scenerio:
>>
>> std::vector<int> vecInt(20, 999);
>>
>> VecInt.assign(20, 0);[/color]
>
>You have the parameters backwards.
>[color=green]
>> do all the 999 values get overwritten or does the vector reassign the
>> memory lso?[/color]
>
>Do you want the memory to be freed and reallocated?
>If so, I know that
>
>std::vector <int> vecInt (999, 20);
>
>{
> std::vector <int> temp ();[/color]

The above declares a function called temp, which isn't what you
wanted.
[color=blue]
> temp.swap (vecInt)
>}[/color]

The canonical way to do this (which very few people seem to get right
for some reason), is:

std::vector<int>().swap(vecInt);

Tom

re: std::vector::assign

"tom_usenet" <tom_usenet@hotmail.com> wrote>
[color=blue][color=green]
> >Do you want the memory to be freed and reallocated?
> >If so, I know that
> >
> >std::vector <int> vecInt (999, 20);
> >
> >{
> > std::vector <int> temp ();[/color]
>
> The above declares a function called temp, which isn't what you
> wanted.[/color]

Yes, silly of me. Thanks.
[color=blue][color=green]
> > temp.swap (vecInt)
> >}[/color]
>
> The canonical way to do this (which very few people seem to get right
> for some reason), is:
>
> std::vector<int>().swap(vecInt);[/color]

I have a question about that. I thought I read somewhere that a
temporary is not modifiable. Isn't the result of the expression
'std::vector <int> ()' (when it is an expression...) a temporary?
So what am I missing?

Regards,
Buster.

re: std::vector::assign

On Thu, 18 Sep 2003 14:53:41 +0100, "Buster" <noone@nowhere.com>
wrote:
[color=blue]
>I have a question about that. I thought I read somewhere that a
>temporary is not modifiable. Isn't the result of the expression
>'std::vector <int> ()' (when it is an expression...) a temporary?
>So what am I missing?[/color]

Temporaries are modifiable, it's just that you can't bind them to
non-const references. e.g. this is illegal:

vecInt.swap(std::vector<int>());

Here a temporary is passed as the argument to swap. This argument is a
non-const reference, so the code is illegal.

So, to summarize, you can call member functions (const or non-const)
on non-const temporaries, but you can't bind them to non-const
references. This is why the standard swap technique works, but some
alternatives don't.

Tom