Re: Deleting items from std::list

From:

Markus Schoder <a3vr6dsg-usenet@yahoo.de>

Newsgroups:

comp.lang.c++

Date:

Tue, 27 Jun 2006 23:04:11 +0200

Message-ID:

<44a19d4b$0$29149$9b4e6d93@newsread4.arcor-online.net>

P.J. Plauger wrote:

"Markus Schoder" <a3vr6dsg-usenet@yahoo.de> wrote in message
news:44a02da0$0$29123$9b4e6d93@newsread4.arcor-online.net...

Howard Hinnant wrote:

In article <1151276851.123572.175280@m73g2000cwd.googlegroups.com>,
"Markus Svilans" <msvilans@gmail.com> wrote:

std::list<int> data;

// [ code here to load data with values ]

std::list<int>::reverse_iterator ri = data.rbegin();

while (ri != data.rend())
{
    // Get next iterator in case ri is erased.
    std::list<int>::reverse_iterator next = ri;
    ++next;

    // Check if ri needs to be erased
    if (*ri == VALUE_TO_ERASE)
    {
        // [ code here to process *ri before erasing ]
        data.erase(ri); // <-- Causes compiler error
    }

    ri = next;
}

Obviously an erase method is not defined for reverse iterators in
std::list.

The solution below is better but just for completeness sake

data.erase(ri.base());

should work.

for (std::list<int>::iterator ri = data.end(); ri != data.begin();)
{
    if (*--ri == VALUE_TO_ERASE)
    {
        // [ code here to process *ri before erasing ]
        ri = data.erase(ri);
    }
}

For completeness sake you have to specify how to make it past the
erased element with your reverse iterator. It's way messier than
for Hinnant's direct solution.

Maybe I wasn't clear enough but I meant to say his (Hinnant's)
solution is better. Just wanted to point out that you can erase
through a reverse iterator. The way I did it is however not correct
since &*(ri.base()-1) == &*ri.