Re: [Boost-users] [multi_index] how to check if an iterator ist still valid

From: joaquin_at_[hidden]
Date: 2008-04-21 13:00:22

Kowalke Oliver (QD IT PA AS) escribió:
> Hi,
> how can I ensure that an iterator is still valid (item was not
> removed from the index)?
>   

Well, there is no legal way to determine whether an iterator is valid or 
not unless you already
have this information from other sources (the state your program is in 
or other contextual info).
The reason is that if you've got an invalid iterator you cannot do 
anything with it except assign
it a new valid value:

iterator it=cont.find(...);
cont.erase(it); // "it" is now invalid
*it; // ILLEGAL
++it; --it; // ILLEGAL
it2=it; // ILLEGAL
foo(it); // ILLEGAL, provided foo accepts "it" by value
it=cont.find(...); // OK

[That said, you can grossly abuse the functionality provided by 
Boost.MultiIndex's safe mode
(http://www.boost.org/doc/libs/1_35_0/libs/multi_index/doc/tutorial/debug.html#safe_mode 
)
to check whether an iterator is valid, but this is totally 
non-recommendable as safe mode is a
debugging aid and not program-level functionality, you really oughtn’t 
do it.]

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo