Why does std::set not have a "contains" member function?

c++ stl stdset
Jabberwocky picture Jabberwocky · Mar 1, 2017 · Viewed 14.6k times · Source

I'm heavily using std::set<int> and often I simply need to check if such a set contains a number or not.

I'd find it natural to write:

if (myset.contains(number))
   ...

But because of the lack of a contains member, I need to write the cumbersome:

if (myset.find(number) != myset.end())
  ..

or the not as obvious:

if (myset.count(element) > 0) 
  ..

Is there a reason for this design decision ?

Answer

Martin Bonner supports Monica picture Martin Bonner supports Monica · Mar 1, 2017

I think it was probably because they were trying to make std::set and std::multiset as similar as possible. (And obviously count has a perfectly sensible meaning for std::multiset.)

Personally I think this was a mistake.

It doesn't look quite so bad if you pretend that count is just a misspelling of contains and write the test as:

if (myset.count(element)) 
   ...

It's still a shame though.

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