[Interest] MSVC 2013 Bug?

[Elvis Stansvik]

2015-11-12 23:22 GMT+01:00 Igor Mironchik <igor.mironchik at gmail.com>:
>
>
> On 13.11.2015 00:44, Thiago Macieira wrote:
>>
>> On Thursday 12 November 2015 23:56:20 Igor Mironchik wrote:
>>>>
>>>> First of all, allocating memory when throwing exceptions is bad
>>>> practice.
>>>> Avoid it by redesigning your code.
>>>
>>> Can you, please, explain why allocating memory when throwing exception
>>> is bad practice? Or just can you give a link on any article about this
>>> question.... Thank you.
>>
>> Because allocating memory in response to an OOM situation is stupid, so
>> std::exception doesn't require it; instead, it uses a pointer that is
>> expected
>> to be valid forever. The exception mechanism uses a pre-allocated buffer
>> so
>> that exceptions can still work in an OOM condition.
>>
>>>> Because toLocal8Bit() returns a QByteArray and QByteArray has an
>>>> operator
>>>> const char*(). Why would it not be possible?
>>>>
>>>> Do note that it compiles, but it's probably incorrect because
>>>> std::runtime_error will probably be carrying a dangling pointer.
>>>>
>>>> Like I said, you should redesign so you don't allocate memory when
>>>> throwing
>>>> exceptions.
>>>
>>> Thank you, I understood. Just interesting why Qt 5.5.1 on Windows
>>> compiled without QT_NO_CAST_FROM_BYTEARRAY and on Linux with this one?
>>
>> It isn't. Your test is faulty. The only piece of code that turns that
>> macro on
>> is moc's own build.
>
>
> I found the problem. The problem on Linux with gcc. In std::runtime_error I
> have:
>
>   class runtime_error : public exception
>   {
>     __cow_string _M_msg;
>
>   public:
>     /** Takes a character string describing the error.  */
>     explicit
>     runtime_error(const string& __arg);
>
> #if __cplusplus >= 201103L
>     explicit
>     runtime_error(const char*);
> #endif
>
> It looks like a bug. c_tor with string should be in __cplusplus macro, but
> not c_tor with const char *

That does look strange indeed. And it seems it's the wrong way around
for several of the other exceptions as well (if I look at my stdexcept
here, gcc 5.2.0).

Elvis

>
> gcc version 5.2.1 20151010 (Ubuntu 5.2.1-22ubuntu2)
>
> --
> Best Regards,
> Igor Mironchik.
>
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