How should be delete for this allocation

Re: How should be delete for this allocation

pavan734@gmail. com wrote:[color=blue]
> Hello, I have a array of double pointers as shown below
>
> dummy_class **ptr[10] ; //assume dummy class to be some c++ class
> I have allocated it like this:
>
> for(int i = 0 ; i<10 ; i++)
> {
> ptr[i] = new dummy_class* [5] ;
> for(int j=0 ; j<5 ; j++) // This 5 is because of previous
> allocation of 5
> {
> ptr[i][j] = new dummy_class ;
> }
> }
>
> 1. Whether the above allocation is valid
> 2. How will be delete statements for this.
>[/color]

1, Looks OK to me.
2. The deallocation needs to mirror the allocations.

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[i][j];
delete ptr[i];
}

Re: How should be delete for this allocation

pavan734@gmail. com wrote:[color=blue]
> Hello, I have a array of double pointers as shown below
>[/color]
<snip code>[color=blue]
>
> 1. Whether the above allocation is valid
> 2. How will be delete statements for this.
>[/color]

Is this homework?

Stewart

Re: How should be delete for this allocation


Ron Natalie wrote:
[color=blue][color=green]
> >[/color]
>
> 1, Looks OK to me.
> 2. The deallocation needs to mirror the allocations.
>
> for(i = 0; i < 10; ++i) {
> for(int j = 0; j < 5; ++j)
> delete ptr[i][j];
> delete ptr[i];
> }[/color]

Thank you. But is it not possible to delete using delete[] ?

Re: How should be delete for this allocation

pavan734@gmail. com wrote:[color=blue]
> Ron Natalie wrote:
>[color=green][color=darkred]
>>>[/color]
>>
>> 1, Looks OK to me.
>> 2. The deallocation needs to mirror the allocations.
>>
>> for(i = 0; i < 10; ++i) {
>> for(int j = 0; j < 5; ++j)
>> delete ptr[i][j];
>> delete ptr[i];
>> }[/color]
>
> Thank you. But is it not possible to delete using delete[] ?[/color]

Ron made a mistake. If you allocated using 'new[]', you should
deallocate using 'delete[]'. The proper deallocation code would
be

for(int i = 0 ; i<10 ; i++) {
for(int j=0 ; j<5 ; j++)
delete ptr[i][j];
delete[] ptr[i];
}

When my OCD is acting up, I even rewrite the loops so that the
deallocations are in the reverse order of allocations:


for(int i = 10 ; i-- >0;) {
for(int j=5 ; j-- >0;)
delete ptr[i][j];
delete[] ptr[i];
}

(I hope I got the indexing correctly :-])

V
--
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I do not respond to top-posted replies, please don't ask

Re: How should be delete for this allocation

pavan734@gmail. com wrote:[color=blue]
> Ron Natalie wrote:
>
>[color=green]
>>1, Looks OK to me.
>>2. The deallocation needs to mirror the allocations.
>>
>>for(i = 0; i < 10; ++i) {
>> for(int j = 0; j < 5; ++j)
>> delete ptr[i][j];
>> delete ptr[i];
>>}[/color]
>
>
> Thank you. But is it not possible to delete using delete[] ?[/color]

Ron's code contained an error - it should be:

for(i = 0; i < 10; ++i) {
for(int j = 0; j < 5; ++j)
delete ptr[i][j];
delete[] ptr[i];
}

Every new you write should have a matching delete, and every new[] and
matching delete[].

Tom

Re: How should be delete for this allocation

Ron Natalie wrote:[color=blue]
> pavan734@gmail. com wrote:[color=green]
>> Hello, I have a array of double pointers as shown below
>>
>> dummy_class **ptr[10] ; //assume dummy class to be some c++ class
>> I have allocated it like this:
>>
>> for(int i = 0 ; i<10 ; i++)
>> {
>> ptr[i] = new dummy_class* [5] ;
>> for(int j=0 ; j<5 ; j++) // This 5 is because of previous
>> allocation of 5
>> {
>> ptr[i][j] = new dummy_class ;
>> }
>> }
>>
>> 1. Whether the above allocation is valid
>> 2. How will be delete statements for this.
>>[/color]
>
> 1, Looks OK to me.
> 2. The deallocation needs to mirror the allocations.
>
> for(i = 0; i < 10; ++i) {
> for(int j = 0; j < 5; ++j)
> delete ptr[i][j];
> delete ptr[i];[/color]

delete[] ptr[i];
[color=blue]
> }[/color]

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

Re: How should be delete for this allocation

Thank you everyone for your kind help.

Re: How should be delete for this allocation


8 posts already in this thread and no-one has suggested that the OP use
std::vector. You guys must be going soft !

Re: How should be delete for this allocation

pavan734@gmail. com wrote:[color=blue]
> Ron Natalie wrote:
>[color=green]
>> 1, Looks OK to me.
>> 2. The deallocation needs to mirror the allocations.
>>
>> for(i = 0; i < 10; ++i) {
>> for(int j = 0; j < 5; ++j)
>> delete ptr[i][j];
>> delete ptr[i];
>> }[/color]
>
> Thank you. But is it not possible to delete using delete[] ?
>[/color]

Actually the last one should be delete[] my mistake.