Thread: Remove element from STL list

Hello,
please, I need to have a list of objects that are frequently inserted and removed.
That's why I decided to use STL list.
However, I have problems removing elements from the list.
For example this code won't compile:

Code:

#include <iostream>
#include <list>
#include <string>

using namespace std;

struct Klijent
{
	string ime;
};


int main()
{
	Klijent k;
	k.ime="Name";

	list<Klijent>lista;

	lista.push_back(k);

	lista.remove(k);
}

One way to slove this is to use iterators:

Code:

for (it = lista.begin(); it != lista.end(); ++it)
{
	if (it->ime == "Name")
	{
		lista.erase(it);
	}
}

but, this gives me an exception. I don't know what is wrong.
I wonder if there is a clever way to do this?
There's been a while since I used STL and I almost forget it.
Thanks in advance.

You would need to provide some way for remove() to compare objects, so you would provide an operator==

Code:

bool operator==(const Klijent& lhs, const Klijent& rhs)
{
    return lhs.ime == rhs.ime;
}

Of course, it makes sense now.
Thanks laserlight

As for the other snippet, when you call erase(it), you invalidate the iterator. Subsequent incrementing of the iterator is undefined behaviour.

If you needed to use the iterator method, erase() returns a valid iterator.

So this:

Code:

if (it->ime == "Name")
{
    it = lista.erase(it);
}

would work.

Thank you people, very helpful...

But if you use the return value of it, the loop logic is broken. The "might-remove" loop is not simple. It looks like this:

Code:

for(container::iterator it = c.begin(); it != c.end(); ) {
  if(condition) {
    it = c.erase(it);
  } else {
    ++it;
  }
}

Originally Posted by CornedBee

But if you use the return value of it, the loop logic is broken. The "might-remove" loop is not simple. It looks like this:

Code:

for(container::iterator it = c.begin(); it != c.end(); ) {
  if(condition) {
    it = c.erase(it);
  } else {
    ++it;
  }
}

Ouch, you're right. I thought it returned an iterator in such a way that allowed continued traversal. Looks like I'll be fixing some code tonight.