finding/counting elements in a STL::map

[Michael H Lees]

Hi all,

As I see it there are two options for checking if for an element with
key 'x' exists in a map m....

1.) if(m.find(x)!=m.end())

or

2.) if(m.count(x))


They both take O(log N) where N is number of elements. Obviously they
both provide different things but which method should you use for just
checking if a key exists? Does it in fact matter? I have seen examples
of both


Thanks

-Mike

 

[Victor Bazarov]

As I see it there are two options for checking if for an element with
key 'x' exists in a map m....

1.) if(m.find(x)!=m.end())

or

2.) if(m.count(x))


They both take O(log N) where N is number of elements. Obviously they
both provide different things but which method should you use for just
checking if a key exists? Does it in fact matter? I have seen examples
of both

It doesn't matter. IMHO, if it's a map<>, where keys are single,
using 'count' is a bit counterintuitive (pun intended). Use whatever
you find more attractive (pun intended).

Victor

 

[David Cattarin]

It doesn't matter. IMHO, if it's a map<>, where keys are single,
using 'count' is a bit counterintuitive (pun intended). Use whatever
you find more attractive (pun intended).

LOL. That's pretty cute.

However, I'd say use whatever you think other people would find
intuitive. If there is any possiblility that someone else will have to
maintain your code, take pitty on the poor slob and use find. Odds are
that using count would just confuse other people.

Dave

 

[Samuele Armondi]

Hi all,

As I see it there are two options for checking if for an element with
key 'x' exists in a map m....

1.) if(m.find(x)!=m.end())

or

2.) if(m.count(x))


They both take O(log N) where N is number of elements. Obviously they
both provide different things but which method should you use for just
checking if a key exists? Does it in fact matter? I have seen examples
of both


Thanks

-Mike

I would stick to find(), as it conveys the meaning of what you are trying to
do. It will save some poor maintenance coder scratching his head over coffee
for 2 hours!
S. Armondi