Am 06.06.2014 21:13, schrieb Junio C Hamano:
> Karsten Blees <karsten.blees@xxxxxxxxx> writes:
>
>> Am 29.05.2014 12:47, schrieb Stepan Kasal:
>>> Fix const warnings in http-fetch.c and remote-curl.c main() where is
>>> argv declared as const.
>>>
>>> The fix should work for all future declarations of main, no matter
>>> whether the second parameter's type is "char**", "const char**", or
>>> "char *[]".
>>
>> I'm 100% in favor of a solution that doesn't restrict main to non-const char**! Thanks.
>>
>>> Signed-off-by: Stepan Kasal <kasal@xxxxxx>
>>> ---
>>> compat/mingw.h | 5 +++--
>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/compat/mingw.h b/compat/mingw.h
>>> index 15f0c9d..8745d19 100644
>>> --- a/compat/mingw.h
>>> +++ b/compat/mingw.h
>>> @@ -369,10 +369,11 @@ extern CRITICAL_SECTION pinfo_cs;
>>> void mingw_startup();
>>> #define main(c,v) dummy_decl_mingw_main(); \
>>> static int mingw_main(c,v); \
>>> -int main(int argc, char **argv) \
>>> +int main(c, char **main_argv_not_used) \
>>> { \
>>> + typedef v, **argv_type; \
>>> mingw_startup(); \
>>> - return mingw_main(__argc, __argv); \
>>> + return mingw_main(__argc, (argv_type)__argv); \
>>> } \
>>> static int mingw_main(c,v)
>>>
>>
>> I have to admit I had trouble understanding what 'typedef v,
>> **arv_type;' does (looks invalid at first glance), and why you
>> would need main_argv_not_used instead of just main(c,v).
>>
>> So, I'd like to award +10 points for cleverness, but -10 for
>> obscurity ;-) Probably deserves a comment or an explanation in the
>> commit message.
>
> Agreed. The "typedef" one is a cute hack.
>
> I am wondering why the solution is not a more obvious "drop const
> that is not ANSI C", though. I only have a ready-access to N1570
> draft but in it I find:
>
Actually, that was the original solution ($gmane/247535). I just complained because it was slightly different from what we had in msysgit for quite some time [1], causing merge conflicts.
I guess compilers probably won't complain if you declare argv const, even if the standard is more strict. After all, you aren't supposed to modify argv.
>
>> A simpler solution that works with all definitions of main() is to
>> cast to void* (tell the compiler all responsibility is on
>> us).
>
> Can you cast away the constness that way, though?
>
Not 'away'. This passes a non-const value to a const parameter, which is typically not a problem. Its just 'char**' to 'const char**' that produces the warning, because 'const char' hides behind a non-const pointer, see [2]. 'void*' to 'const char**' works, though.
[1] https://github.com/msysgit/git/commit/6949537a
[2] http://c-faq.com/ansi/constmismatch.html
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html