std::regex: inserting std::wregex to std::vector loses some std::wregex values

[Paolo Carlini]

Hi,

On 09/14/2014 08:12 PM, Tim Shen wrote:
> On Sun, Sep 14, 2014 at 3:16 AM, Paolo Carlini <paolo.carlini@oracle.com> wrote:
>> Thus, are you going to send an actual patch? I'm wondering if we could
>> arrange it in such a way not to break the binary compatibility in the
>> release branch (thus fix the bug there too) perhaps by not removing any data
>> members, simply leaving them unused?! In mainline I suppose we are going to
>> stabilize the ABI for the 5.0 release, thus we can do that. While we are at
>> it, check that the order of the final remaining data members is still
>> optimal size-wise.
> I've made a patch that changes basic_regex's member only, by making
> basic_regex::_M_traits heap allocated.
Thanks. Maybe Jon can have a closer look to it...
> I believe that I didn't get it, but I'm still a little bit confused,
> since we haven't instantiated and exported any regex class (except
> regex_error, I suppose) to the binary, right?
>
> Anyway, the patch is bootstrapped and tested with debug flag. Can it
> be modified slightly to keep the binary compatibility?
Probably yes, but then, as described here:

     https://gcc.gnu.org/onlinedocs/libstdc++/manual/abi.html

under <prohibited changes>, you cannot add or remove the basic_regex 
data members. This doesn't have much to do with the exported symbols, 
the mental model is somebody including the old <regex> compiling an a.o, 
then including the new <regex> and compiling a b.o, then linking 
together a.o and b.o: things must work fine in every case.

Paolo.