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Re: [PATCH,c++] use XALLOCAVEC in the C++ front-end
On Wed, Jun 9, 2010 at 6:53 AM, Manuel López-Ibáñez
<lopezibanez@gmail.com> wrote:
> On 9 June 2010 13:33, Gabriel Dos Reis <gdr@integrable-solutions.net> wrote:
>> On Wed, Jun 9, 2010 at 4:53 AM, Manuel López-Ibáñez
>> <lopezibanez@gmail.com> wrote:
>>> On 8 June 2010 18:14, Jason Merrill <jason@redhat.com> wrote:
>>>> On 06/08/2010 10:43 AM, Manuel López-Ibáñez wrote:
>>>>>
>>>>> On 8 June 2010 16:06, Jason Merrill<jason@redhat.com> ?wrote:
>>>>
>>>>>> The error message is unclear, but the issue is that converting from
>>>>>> char**
>>>>>> to char const** is unsafe, while converting to char const*const* is safe.
>>>>>
>>>>> What does it mean unsafe in this context? I could produce a patch that
>>>>> changes the message but I would like to be sure what to say.
>>>>>
>>>>> semantics.c:1223:7: error: new ‘const’ qualifier in cast from 'char
>>>>> **' to 'const char **' is unsafe [-Werror=cast-qual]
>>>> Explanation from the C++ standard (4.4 [conv.qual]):
>>>>
>>>> [ Note: if a program could assign a pointer of type T** to a pointer of type
>>>> const T** (that is, if line #1 below were allowed), a program could
>>>> inadvertently modify a const object (as it is done on line #2). For example,
>>>>
>>>> ?int main() {
>>>> ? ?const char c = ’c’;
>>>> ? ?char* pc;
>>>> ? ?const char** pcc = &pc;// #1: not allowed
>>>> ? ?*pcc = &c;
>>>> ? ?*pc = ’C’; // #2: modifies a const object
>>>> ?}
>>>> --end note ]
>>>
>>> So what do you think about the following message:
>>>
>>> error: new ‘const’ qualifier in cast from 'char **' to 'const char **'
>>> is unsafe [-Werror=cast-qual]
>>> note: to be safe all intermediate pointers must be equally qualified
>>
>> that is OK; but I find the leading 'new' hard to parse. ? Please, just
>> remove it.
>>
>
> Anyway, this is the C FE.
Yes, I know.
> The C++ FE gives the following:
>
> test.C:4:23: warning: invalid conversion from ‘char**’ to ‘const
> char**’ [-fpermissive]
>
> but the code is too intricate to give a clearer error in the case of
> C++ or to factor out the common check.
Removing the leading 'new' does not require any of that.
>
> Cheers,
>
> Manuel.
>