CODEWITHSUNDEEP
c++stlset
herzl shemuelian
herzl shemuelian

Reputation: 3508

Erase final member of std::set

How can I delete the last member from a set?

For example: 

set<int> setInt;
setInt.insert(1);
setInt.insert(4);
setInt.insert(3);
setInt.insert(2);

How can I delete 4 from setInt? I tried something like:

 setInt.erase(setInt.rbegin());

but I received an error.

Upvotes: 39

Views: 20156

Answers (6)

bitmask
bitmask

Reputation: 34714

Edit: You should use std::prev as shown in Benjamin's better answer instead of the older style suggested in this answer.

I'd propose using a different name for rbegin which has a proper type:

setInt.erase(--setInt.end());

Assuming you checked that setInt is not empty!

Btw. this works because you can call the mutating decrement operator on a temporary (of type std::set<int>::iterator). This temporary will then be passed to the erase function.

Upvotes: 9

Madiyar
Madiyar

Reputation: 1089

A bit less performant, but an alternative option:

setInt.erase(*setInt.rbegin());

Upvotes: 4

Steve Jessop
Steve Jessop

Reputation: 279455

if (!setInt.empty()) {
    std::set<int>::iterator it = setInt.end();
    --it;
    setInt.erase(it);
}

By the way, if you're doing this a lot (adding things to a set in arbitrary order and then removing the top element), you could also take a look at std::priority_queue, see whether that suits your usage.

Upvotes: 25

Totonga
Totonga

Reputation: 4366

If you want to delete 4 instead of the last you should use the find method. Depending on the use case 4 might not be the last. 

std::set<int>::iterator it = setInt.find(4);
if(it != setInt.end()) {
  setInt.erase(it);
}

If you want to delete the last element use:

if (!setInt.empty()) {
  setInt.erase(--setInt.rbegin().base());
  // line above is equal to 
  // setInt.erase(--setInt.end());
}

While I was not sure if --*.end(); is O.K. I did some reading. So the -- on rbegin().base() leads to the same result as -- on end(). And both should work.

Upvotes: 1

Karai
Karai

Reputation: 298

Check if the set is empty or not. If not, then get the last element and set that as iterator and reduce that iterator and erase the last element.

if (!setInt.empty())
 {
    std::set<int>::iterator it = setInt.end();
    --it;
    if(it != setInt.end()) {
    setInt.erase(it);
    } 
 }

Upvotes: 0

Benjamin Lindley
Benjamin Lindley

Reputation: 103761

in C++11

setInt.erase(std::prev(setInt.end()));

You can decide how you want to handle cases where the set is empty.

Upvotes: 51

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