Re: [Boost-users] boost multi-index container find method.

Subject: Re: [Boost-users] boost multi-index container find method.
From: Joaquin M Lopez Munoz (joaquin_at_[hidden])
Date: 2009-09-17 15:25:12

Ramesh <rramesh1 <at> gmail.com> writes:

> 
> Hello Joaquin,

Hi Ramesh,

> I have a class like below that uses mult-index container's find
> method. Â I have a record pattern as below initially:
> 
> Idx : 100 Flag : 5
> Idx : 200 Flag : 5
> Idx : 300 Flag : 5
> Idx : 400 Flag : 5
> 
[...]
> 
> Idx : 200 flag : 5
> 
> While find functionally is correct in picking up the correct data, but
> I am wondering why it doesnt pick the first record (100) which has the
> flag value set to 5?

find() returns an element with the searched key
in case there is one, but note that no guarantee is made
about which element is returned when there are several
to choose from (in case you're curious: ordered indices
are internally implemented as rd-trees, and find simply
returns the first element found when traversing the
tree topdown).

Even if you use lower_bound() to find the first element
of the range, there is no guarantee that (100,5) appears
the first on the flag-based index. You can follow Igor's
advice on using a composite key here.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo