Memory allocation with void pointer

[Maedowan]

Does this code delete right amount of memory:

struct SAMPLE{
int a,b,c;
char zzz;
};

void* ptr;
int main()
{
ptr=(void*) new[SAMPLE];
delete ptr; //delete void pointer without casting it
}

[John Harrison]

Re: Memory allocation with void pointer


"Maedowan" <Maedowan@gaz.p l> wrote in message
news:chhnfc$c4c $3@inews.gazeta .pl...[color=blue]
> Does this code delete right amount of memory:
>
> struct SAMPLE{
> int a,b,c;
> char zzz;
> };
>
> void* ptr;
> int main()
> {
> ptr=(void*) new[SAMPLE];
> delete ptr; //delete void pointer without casting it
> }[/color]

No, the behaviour of this program is completely undefined by the C++
standard. It might be OK, it might not.

john

[Maedowan]

Re: Memory allocation with void pointer

John Harrison wrote:
[color=blue]
>
> "Maedowan" <Maedowan@gaz.p l> wrote in message
> news:chhnfc$c4c $3@inews.gazeta .pl...[color=green]
>> Does this code delete right amount of memory:
>>
>> struct SAMPLE{
>> int a,b,c;
>> char zzz;
>> };
>>
>> void* ptr;
>> int main()
>> {
>> ptr=(void*) new[SAMPLE];
>> delete ptr; //delete void pointer without casting it
>> }[/color]
>
> No, the behaviour of this program is completely undefined by the C++
> standard. It might be OK, it might not.[/color]

but what about free and malloc, they use void* pointers and does it right.

[John Harrison]

Re: Memory allocation with void pointer


"Maedowan" <Maedowan@gaz.p l> wrote in message
news:chhqi8$sqk $3@inews.gazeta .pl...[color=blue]
> John Harrison wrote:
>[color=green]
> >
> > "Maedowan" <Maedowan@gaz.p l> wrote in message
> > news:chhnfc$c4c $3@inews.gazeta .pl...[color=darkred]
> >> Does this code delete right amount of memory:
> >>
> >> struct SAMPLE{
> >> int a,b,c;
> >> char zzz;
> >> };
> >>
> >> void* ptr;
> >> int main()
> >> {
> >> ptr=(void*) new[SAMPLE];
> >> delete ptr; //delete void pointer without casting it
> >> }[/color]
> >
> > No, the behaviour of this program is completely undefined by the C++
> > standard. It might be OK, it might not.[/color]
>
> but what about free and malloc, they use void* pointers and does it right.[/color]

free and malloc would be fine. There's no reason you can't use them in a C++
program.

john

[Maedowan]

Re: Memory allocation with void pointer

John Harrison wrote:
[color=blue]
>
> free and malloc would be fine. There's no reason you can't use them in a
> C++ program.[/color]

becouse i don't want to include stdlib, it will incrase size of my
executable. Is this code proper in c++ :

void* ptr=new SAMPLE;
delete (SAMPLE*) ptr; //casting ptr to proper type.

[John Harrison]

Re: Memory allocation with void pointer


"Maedowan" <Maedowan@gaz.p l> wrote in message
news:chhrdh$sqk $6@inews.gazeta .pl...[color=blue]
> John Harrison wrote:
>[color=green]
> >
> > free and malloc would be fine. There's no reason you can't use them in a
> > C++ program.[/color]
>
> becouse i don't want to include stdlib, it will incrase size of my
> executable. Is this code proper in c++ :
>
> void* ptr=new SAMPLE;
> delete (SAMPLE*) ptr; //casting ptr to proper type.[/color]

That's fine.

Remember that if you allocate an array then you must use delete[] when you
deallocate (this was the other thing wrong with your original code)

void* ptr=new SAMPLE[10];
delete[] (SAMPLE*) ptr; // use delete[] for arrays

john

[Gianni Mariani]

Re: Memory allocation with void pointer

Maedowan wrote:[color=blue]
> John Harrison wrote:
>
>[color=green]
>>free and malloc would be fine. There's no reason you can't use them in a
>>C++ program.[/color]
>
>
> becouse i don't want to include stdlib, it will incrase size of my
> executable. ...[/color]

It is unlikely that including stdlib will increase the size of your
executable at all.

[color=blue]
> ... Is this code proper in c++ :
>
> void* ptr=new SAMPLE;
> delete (SAMPLE*) ptr; //casting ptr to proper type.[/color]

The snipped above would work fine.

You can also use "operator new".

int main()
{
void * x = operator new( 50 );

operator delete( x );
}

[Maedowan]

Re: Memory allocation with void pointer

John Harrison wrote:

[color=blue]
>
> Remember that if you allocate an array then you must use delete[] when you
> deallocate (this was the other thing wrong with your original code)
>
> void* ptr=new SAMPLE[10];
> delete[] (SAMPLE*) ptr; // use delete[] for arrays
>[/color]

my orginal code wouldn't even compile becouse i wrote like this:
new[SAMPLE], i don't now why i wrote like this but i did it

[Maedowan]

Re: Memory allocation with void pointer

Gianni Mariani wrote:

[color=blue][color=green]
>> ... Is this code proper in c++ :
>>
>> void* ptr=new SAMPLE;
>> delete (SAMPLE*) ptr; //casting ptr to proper type.[/color]
>
> The snipped above would work fine.
>
> You can also use "operator new".
>
> int main()
> {
> void * x = operator new( 50 );
>
> operator delete( x );
> }[/color]

that is interesting, doesn't delete use operator delete(), if it calls this
operator i think it's also possible to use delete sample;

[Gianni Mariani]

Re: Memory allocation with void pointer

Maedowan wrote:
....[color=blue]
>
> that is interesting, doesn't delete use operator delete(), if it calls this
> operator i think it's also possible to use delete sample;[/color]

Be more clear about your question - post a code snippet of what you mean
you think you can do.