Re: [Consult] g++: About "-Wunused-variable" for constant variable in header file

[Chen Gang <gang.chen.5i5j@gmail.com>]

On 10/15/14 17:18, Jonathan Wakely wrote:
> On 14 October 2014 22:57, Chen Gang <gang.chen.5i5j@gmail.com> wrote:
>> Hello All:
>>
>> At present, I met one warning issue about gcc 5.0.0.
>>
>>  - For "const float a = 3.4 - 2.1 / 3;", if it is unused, gcc5 will not
>>    report warning.
> 
> Because there is no cost to initializing the variable.
> 
>>  - "const char n() {return 1;}; const a = n();", if 'a' is unused, gcc5
>>    will report warning.
> 
> Because it requires dynamic initialization, running a function at
> startup, which has a cost. If you don't use the variable then you
> might not want to run the initialization code at startup, so you get a
> warning.
> 
>> For gcc old version (e.g. gcc4), it will not report warning. Is it the
>> new feature for gcc5, or just a gcc5's bug?
> 
> I think this behaviour is intended and is not a bug.
> 

Thank you very much four your details reply! And thank Jakub Jelinek for
the almost same reply in another original mailing thread, too.

I shall forward your reply to the other related mail thread which is
related with QEMU.

Thanks again.  :-)

-- 
Chen Gang

Open, share, and attitude like air, water, and life which God blessed