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]

Re: finding/counting elements in a STL::map

"Michael H Lees" <mhl@cs.nott.ac .uk++> wrote...[color=blue]
> 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[/color]

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

Victor

[David Cattarin]

Re: finding/counting elements in a STL::map

"Victor Bazarov" <v.Abazarov@att Abi.com> wrote in message news:<vflubl982 nca0f@corp.supe rnews.com>...[color=blue]
> "Michael H Lees" <mhl@cs.nott.ac .uk++> wrote...[color=green]
> > 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[/color]
>
> It doesn't matter. IMHO, if it's a map<>, where keys are single,
> using 'count' is a bit counterintuitiv e (pun intended). Use whatever
> you find more attractive (pun intended).[/color]

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]

Re: finding/counting elements in a STL::map


"Michael H Lees" <mhl@cs.nott.ac .uk++> wrote in message
news:bdeqoj$mv8 $1@oyez.ccc.not tingham.ac.uk.. .[color=blue]
> 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
>[/color]
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