How do I update a member in a set of std::pair?

Question

I tried doing this:

std::set< pair<int, int> > mySet;

// fill the set with something

mySet.find( make_pair(someValueX, someValueY) )->first = newX;

But I get the following error on compilation:

error: assignment of member 'std::pair<int, int>::first' in read-only object|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===||

You can't, you need to remove the pair and insert the new one. — user4815162342, Mar 01 '17 at 17:19
This has nothing to do with `std::pair`, it's a limitation imposed by `std::set`. — François Andrieux, Mar 01 '17 at 17:19

score 8 · Answer 1 · answered Mar 01 '17 at 17:19

8

Members of std::set are const, because changing them could make their ordering invalid. You would have to erase the pair and re-insert it after it was changed.

answered Mar 01 '17 at 17:19

alain

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Oh, now I understand... This was bugging me for some time and had no idea why it didn't work. Thanks! – Tudor Versoiu Mar 01 '17 at 17:24

How do I update a member in a set of std::pair?

1 Answers1