get current iterator from for(int &i : i)

Question

This is my loop;

for (sf::TcpSocket &client : clients)
{
    ...
}

In the loop, I would like to check if someone has disconnected, and if so, remove them from the list of users, I just don't know how to check which user it is up to in the list.

The list of users is a vector of 100 sf::tcpsockets in the loop if someone has disconnected I just skip the rest of the code with a continue statement.

I check if they have disconnected by sending "ping" over and if no response is given, then they disconnected.

There is one list of users, that being named clients

Meta answer: Don't use this kind of loop if you want to modify the range itself. — Baum mit Augen, May 30 '17 at 11:16
What's the list of users? And actual `std::list`? Or something with random access like a `std::vector` that you wish to index into? Or the `client` you have a reference to? — doctorlove, May 30 '17 at 11:17
If you then try to delete things from `clients` while you iterate over them BAD STUFF will happen — doctorlove, May 30 '17 at 11:18
Just bare in mind that mutating data whilst iterating over it is a bad idea, — Halfpint, May 30 '17 at 11:20
@InternetAussie Please don't approve edits like this, the question is *not* about smfl, so the tag is irrelevant. — Baum mit Augen, May 30 '17 at 11:22
Do we have two "lists" (vectors): clients and users? Or one "list"? — doctorlove, May 30 '17 at 11:23
I answered auto it = std::find(std::begin(clients), std::end(clients), client); Got a lot if downvotes, which i don't understand, because it's a direct answer to the question. That the approach to the problem is bad is not my fault, and he did not ask for another approach. I agree with remove_if is probably what you're are looking for. — lars, May 30 '17 at 11:28
@lars That's not a valid reason to give bad or incomplete advice. Your answer was not useful. — Baum mit Augen, May 30 '17 at 11:29

Gambit · Accepted Answer · 2017-05-30T12:57:29.097

1

Range based for loops are not supposed to be for modification of the container itself. If you wish to add or remove elements from the container, you should use a standard for loop:

for (auto it = std::begin(clients); it != std::end(clients);)
{
    sf::TcpSocket& client = *it;
    // accept data from the client socket

    if (acceptStatus == sf::Socket::Disconnected)
    {
        it = clients.erase(it);
        erased = true;
    }
    else
    {
        ++it;
    }
}

Notice that the iterator is not incremented as part of the for loop post condition. If we did this, when an element is erased the iterator will be incremented which is not what you want because you will accidentally skip an element.

edited May 30 '17 at 12:57

answered May 30 '17 at 11:30

Gambit

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3

That `bool` is very noisy. Just use an `else`? – Lightness Races in Orbit May 30 '17 at 11:50
You can use an `else` if you want it doesnt really matter. – Gambit May 30 '17 at 12:41
2

It certainly does "matter". – Lightness Races in Orbit May 30 '17 at 12:45

get current iterator from for(int &i : i)

1 Answers1