Re: [boost] Re: Formal Review: FOREACH macro

From: Stefan Strasser (sstrasser_at_[hidden])
Date: 2005-05-02 13:58:12

Eric Niebler schrieb:

>>
>> Incidently, if it is caching then code like:
>>
>>     BOOST_FOREACH( int i, vec )
>>         if (condition(i))
>>             vec.push_back( filter(i) );
>>
>> will not work the same as:
>>

vec.reserve(a lot);

>>     for (iterator i = vec.begin(); i != vec.end(); ++i)
>>         if (condition(*i))
>>             vec.push_back( filter(*i) );
>>
> 
> 
> Neither of these loops "work" -- they are both broken in the same way. 
> They both invalidate the iterator they are using.

[5] A vector's iterators are invalidated when its memory is reallocated. 
Additionally, inserting or deleting an element in the middle of a vector 
invalidates all iterators that point to elements following the insertion 
or deletion point. It follows that you can prevent a vector's iterators 
from being invalidated if you use reserve() to preallocate as much 
memory as the vector will ever use, and if all insertions and deletions 
are at the vector's end.

i is never following the insertion point.

-- 
Stefan Strasser