Erasing from middle of a list problem

[Angus]

If I want to erase all list items with a value of say 3 as below:

std::list<int> mylist;
mylist.push_back(3);
mylist.push_back(4);
mylist.push_back(5);
mylist.push_back(6);

for(std::list<int>::iterator it = mylist.begin(); it !=
mylist.end(); ++it) {
if(*it == 3) {
std::cout << "deleting 3" << std::endl;
mylist.erase(it);
}
}

I get an access violation in the loop iteration after an erase. What
is the recommended way to deal with this? ie iterate through a
container removing elements which meet a criterion? remove?

A

 

[fungus]

I get an access violation in the loop iteration after an erase.

Yep, you just freed the memory referenced by "it".

What
is the recommended way to deal with this? ie iterate through a
container removing elements which meet a criterion?  remove?

std::list<int>::iterator it = mylist.begin();
while (it != mylist.end()) {
if(*it == 3) {
std::cout << "deleting 3" << std::endl;
it = mylist.erase(it);
}
else {
++it;
}
}

 

[Marcel Müller]

for(std::list<int>::iterator it = mylist.begin(); it !=
mylist.end(); ++it) {
if(*it == 3) {
std::cout << "deleting 3" << std::endl;
mylist.erase(it);
}
}

I get an access violation in the loop iteration after an erase.

Of course, you just invalidated your iterator by erasing its element.

What
is the recommended way to deal with this?

erase returns an iterator to the next valid element.

ie iterate through a
container removing elements which meet a criterion? remove?

The algorithm remove_if will do the job for you.


Marcel