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Yi
Guest
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 Posted: Wed Aug 23, 2006 9:10 am Post subject: delete dynamically allocated memory in a list? |
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Two questions about the following code sample:
--- code begins ---
//class IPv4 is defined elsewhere
list<IPv4> ip_list;
for (int i=1; i<=9; i++) {
char addr[128];
sprintf(addr, "%d.%d.%d.%d", i,i,i,i);
//IPv4 new_ip(addr);
//ip_list.push_back(new_ip);
ptr = new IPv4(addr);
ip_list.push_back(*ptr);
}
....
list<IPv4>::iterator k;
k = ip_list.begin();
while (k!=pp_list.end()) {
delete &pp_list.front();
pp_list.pop_front();
k = pp_list.begin();
}
--- code ends ---
When I try to free the memory using delete, the program run into error
saying "double free or corruption". I don't know why. How am I supposed
to delete the dynamically allocated memory in a list?
By the way, if I use the two statement that are currently commented in
the first for loop instead of the two statements below them, I don't
need to worry about freeing the memory, right?
Thanks! |
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David Harmon
Guest
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| Posted: Wed Aug 23, 2006 9:10 am Post subject: Re: delete dynamically allocated memory in a list? |
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On 22 Aug 2006 23:09:39 -0700 in comp.lang.c++, "Yi"
<wymail (AT) gmail (DOT) com> wrote,
| Quote: | And one more dumb question: since the scope of new_ip is within the
pair of { }, there is no problem of repeated definitions among
iterations, right?
|
Right, it is automatically created and destroyed for each iteration,
but only one at a time. |
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Vikram
Guest
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| Posted: Wed Aug 23, 2006 9:10 am Post subject: Re: delete dynamically allocated memory in a list? |
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Yi wrote:
| Quote: | You should do a delete ptr above and not delete a list element. They
are different objects.
Do you mean the following?
for (int i=1; i<=9; i++) {
char addr[128];
sprintf(addr, "%d.%d.%d.%d", i,i,i,i);
//IPv4 new_ip(addr);
//pp_list.push_back(new_ip);
ptr = new IPv4(addr);
pp_list.push_back(*ptr);
delete ptr;
}
...
As I asked in the previous post, is it simpler to just use the
following code?
for (int i=1; i<=9; i++) {
char addr[128];
sprintf(addr, "%d.%d.%d.%d", i,i,i,i);
IPv4 new_ip(addr);
pp_list.push_back(new_ip);
//ptr = new IPv4(addr);
//pp_list.push_back(*ptr);
//delete ptr;
}
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Yes...either of the above is fine. In one case you take care of delete
and in the second (which is more convenient) the local variable cleanup
gets automatically done. I would personally go with the second approach
( new_ip). |
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Yi
Guest
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| Posted: Wed Aug 23, 2006 9:10 am Post subject: Re: delete dynamically allocated memory in a list? |
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Thanks a lot Vikram!
| Quote: |
You should do a delete ptr above and not delete a list element. They
are different objects.
|
Do you mean the following?
for (int i=1; i<=9; i++) {
char addr[128];
sprintf(addr, "%d.%d.%d.%d", i,i,i,i);
//IPv4 new_ip(addr);
//pp_list.push_back(new_ip);
ptr = new IPv4(addr);
pp_list.push_back(*ptr);
delete ptr;
}
....
As I asked in the previous post, is it simpler to just use the
following code?
for (int i=1; i<=9; i++) {
char addr[128];
sprintf(addr, "%d.%d.%d.%d", i,i,i,i);
IPv4 new_ip(addr);
pp_list.push_back(new_ip);
//ptr = new IPv4(addr);
//pp_list.push_back(*ptr);
//delete ptr;
}
Thanks a lot! |
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Vikram
Guest
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| Posted: Wed Aug 23, 2006 9:10 am Post subject: Re: delete dynamically allocated memory in a list? |
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Yi wrote:
| Quote: | Two questions about the following code sample:
--- code begins ---
//class IPv4 is defined elsewhere
list<IPv4> ip_list;
for (int i=1; i<=9; i++) {
char addr[128];
sprintf(addr, "%d.%d.%d.%d", i,i,i,i);
//IPv4 new_ip(addr);
//ip_list.push_back(new_ip);
ptr = new IPv4(addr);
ip_list.push_back(*ptr);
|
Note that here a *copy* of *ptr is pushed into the list. It is not the
same object.
| Quote: | }
...
list<IPv4>::iterator k;
k = ip_list.begin();
while (k!=pp_list.end()) {
delete &pp_list.front();
|
This does not fit here. Your list element is an object and not a
pointer. So you should not be deleting it.
| Quote: | pp_list.pop_front();
k = pp_list.begin();
}
--- code ends ---
When I try to free the memory using delete, the program run into error
saying "double free or corruption". I don't know why. How am I supposed
to delete the dynamically allocated memory in a list?
|
You should do a delete ptr above and not delete a list element. They
are different objects.
Hope this helps. |
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Yi
Guest
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| Posted: Wed Aug 23, 2006 9:10 am Post subject: Re: delete dynamically allocated memory in a list? |
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Yeah, I agree!
And one more dumb question: since the scope of new_ip is within the
pair of { }, there is no problem of repeated definitions among
iterations, right?
| Quote: | for (int i=1; i<=9; i++) {
char addr[128];
sprintf(addr, "%d.%d.%d.%d", i,i,i,i);
IPv4 new_ip(addr);
pp_list.push_back(new_ip);
//ptr = new IPv4(addr);
//pp_list.push_back(*ptr);
//delete ptr;
}
Yes...either of the above is fine. In one case you take care of delete
and in the second (which is more convenient) the local variable cleanup
gets automatically done. I would personally go with the second approach
( new_ip). |
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