Re:Re: Local class name conflict

[chenzhelu <chenzero at netease dot com>]

Resend for easy reading. Thanks!

On 2018-01-16 14:45, Andrew Pinski wrote:
> On Mon, Jan 15, 2018 at 10:35 PM, chenzhelu <chenzero@netease.com> wrote:
>> Hello all,
>> I encountered a problem on "local class name conflict",
>> I searched on net and found that years ago, some people also encoutered this kind of problem.
>
> The correct name for this is One Definition Rule (or ODR for short).
> Basically a violation of this rule causes the code to be invalid (with
> no diagnostic required; therefor undefined code).  If you use LTO, GCC
> sometimes will warn about this violation.

Thanks for suggestion!
Yes, this test code is intent to create local classes with same name, for a small project,
it's easy to find out this error, consider a big project...
The root cause is, it's possible that two local classes with same name in a namespace,
(or the default anonymous namespace),
I know that it violate with ODR, however, the point is, it seems that compiler is somehow
not consistent in the Compile and Link phase, that's what I confused of.

>
> If you want a truly local class, then use anonymous namespaces which
> is designed to fix this issue.
This will rely on human to keep local class name unique within a namspace, or the default
anonymous namespace. consider a project with hundreds  of files. 
As a precise software, I think it'd better not allow this undefined behavior open,
whether the compile better give some warning/error on this name conflicts,
or link with the "nearest" local class ?

Thanks!

>
> Thanks,
> Andrew
>
>>
>> https://stackoverflow.com/questions/10671956/same-class-name-in-different-c-files
>> http://www.cplusplus.com/forum/general/32010/
>>
>>
>> Please see the following code, (BTW, it seems that the maillist can not attach files)
>>
>> When I ran the code(Ubuntu 64bis, gcc vesion:5.4.0, the amazing result is :
>> localClassXInData.cpp in Data.cpp
>>   localClassXInData.cpp in Data.cpp
>>
>>
>> I think there is an error in Link phrase:
>> 1. if comment out the LocalClassX definition in main.cpp, the compile will not compile the code --- this is as expected.
>> 2. however, if run the code(not comment out any code), the code actually ran is in the Data.cpp, that is not consistent with compile phase.
>>
>>
>> Thanks!