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Date: Sun, 02 Mar 2014 22:50:01 +0100
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To: cygwin AT cygwin DOT com
Subject: Re: va_list and char* are ambiguous
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On 03/02/2014 10:45 PM, Irfan Adilovic wrote:
> On Sun, Mar 2, 2014 at 6:58 PM, Irfan Adilovic wrote:
>> irfan AT irfy:~$ cat x.cc
>> #include <cstdarg>
>> #include <iostream>
>> using namespace std;
>> void foo (...)        { cout << "varargs\n"; }
>> void foo (va_list ap) { cout << "va_list\n"; }
>> int main () {
>>     foo ((const char *)NULL);
>>     foo ((char *)NULL);
>> }
>> irfan AT irfy:~$ make x
>> g++     x.cc   -o x
>> irfan AT irfy:~$ ./x
>> varargs
>> va_list
>> $ uname -a
>> CYGWIN_NT-6.2 irfy 1.7.29(0.271/5/3) 2014-02-21 23:45 x86_64 Cygwin
>>
>> I would expect the varargs version of foo to be called both times --
>> and it does on my linux machine -- but I get the above output under
>> Cygwin. It looks like va_list is defined in terms of char*.
>>
>> Can anyone confirm this behavior on their Cygwin installations?
>>
>> Is this behavior legal? (in terms of whatever standards apply)
>>
>> Is there a way to "fix" this? (i.e. typedef va_list as a pointer to a
>> struct defined just for the purpose of defining the va_list type)
>>
>> -- Irfan
>=20
> I forgot to mention that calling `foo ("");` will produce:
>=20
> x.cc:7:12: warning: deprecated conversion from string constant to
> 'char*' [-Wwrite-strings]
>      foo ("");
>             ^
>=20
> at compile time and will end up calling va_list at runtime.
I suspect this is due to compatibility with MS compiler on 32 bit
windows, where va_list is also char*.

Does it fail for AMD64 as well? I suspect it should not and it should
work. IIRC the AMD64 MS compiler uses different definition than the 32
bit one. (I cannot check right now.)

I do not think there is much that can be done about it. You will simply
have to rename one of the functions.

--=20
VZ



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