Re: [boost] [filesystem] How to remove specific files from a directory?

Subject: Re: [boost] [filesystem] How to remove specific files from a directory?
From: Mateusz Loskot (mateusz_at_[hidden])
Date: 2016-09-07 10:59:28

On 7 September 2016 at 16:45, Andrey Semashev <andrey.semashev_at_[hidden]> wrote:
> On 09/07/16 17:07, Mateusz Loskot wrote:
>> On 7 September 2016 at 15:46, Andrey Semashev <andrey.semashev_at_[hidden]> wrote:
>>> On 09/07/16 16:06, Andrzej Krzemienski wrote:
>>>>
>>>>
>>>> Hi,
>>>> I wonder what is boost::filesystem recommendation for solving the
>>>> following
>>>> problem.
>>>>
>>>> I want to remove all files from a given directory that satisfy a certain
>>>> predicate, e.g., only these whose names start with letter "s".
>>>>
>>>> It is my understanding that the calling filesystem::remove may
>>>> invalidate
>>>> the iterator, and therefore the following solution is incorrect:
>>>>
>>>> fsys::directory_iterator it{path}, itEnd{};
>>>> for ( ; it != itEnd ; ++it )
>>>> {
>>>>   if (predicate(*it))
>>>>     fsys::remove(it->path());
>>>> }
>>>>
>>>> But, is the following guaranteed to work?:
>>>>
>>>> fsys::directory_iterator it{path}, itEnd{};
>>>> for ( ; it != itEnd ; )
>>>> {
>>>>   if (predicate(*it))
>>>>     fsys::remove((it++)->path());
>>>>   else
>>>>     ++it;
>>>> }
>>>
>>>
>>>
>>> From the documentation, it seems the behavior should be similar to
>>> readdir,
>>> in which case it would seem that both pieces of code above are valid.
>>
>>
>> Indeed, boost::filesystem and std::filesystem (ISO/IEC TS 18822:2015) as
>> well
>> as POSIX readdir behave in the same way.
>> But, for all of them, behaviour is unspecified in case content of
>> directory that is
>> being traversed changes.
>
>
> It is unspecified whether the removed/added files will be discovered as part
> of the traversal. Other than that the behavior is defined. For instance, the
> implementation should not crash and the iterator should still reach the end
> at some point.

Right, the iteration following any changes in the filesystem content
remains valid.
Thanks for the correction.

Best regards,
-- 
Mateusz Loskot, http://mateusz.loskot.net