[cfe-dev] Why this extern "C" fails ?

[Ólafur Waage]

I don't remember if there is a direct reference for this statement, I think
it is more a result of the language rules surrounding it. Devchandra's
quote is the most direct one I think.

Lets say this example of yours would work. How  would you reference this
variable you just made?


On Tue, Jul 30, 2013 at 5:44 AM, Arji Cot <arjicot at gmail.com> wrote:

> "extern symbols should be in a global scope"
>
> Can you provide a reference for this statement ?
>
>
> 2013/7/29 Renato Golin <renato.golin at linaro.org>
>
>> On 29 July 2013 14:56, Arji Cot <arjicot at gmail.com> wrote:
>>
>>> --------------
>>>
>>> #include <iostream>
>>>
>>> int main() {
>>>   {
>>>     extern "C" { int a = 42; }
>>>     { std::cout << a << "\n"; }
>>>   }
>>>   return (0);
>>> }
>>
>>
>> Hi Arji,
>>
>> As Olafur said, extern symbols should be in a global scope, and that "a"
>> couldn't even be seen from the next line, and you'd see another error from
>> the compiler if you removed the extern.
>>
>>
>> main.cpp:5:12: error: expected unqualified-id
>>>      extern "C" { int a = 42; }
>>>            ^
>>> 1 error generated.
>>>
>>> It's not enough to me to explain why this is not working.
>>>
>>
>> Every compiler error assumes familiarity with the language, at least
>> enough to go and look at the definition of the terms involved in the error
>> message (extern "C" in this case) in a book, on the web or the standard,
>> which should give you enough information on how to fix the bug.
>>
>> Compilers are famous for not giving enough information on error messages,
>> and Clang stands out as being one of the best on that side, but no compiler
>> will ever teach you the language via error messages.
>>
>> One rule of thumb is to use a different compiler and see if it also gives
>> you an error, maybe a different error, or a better error message, or none
>> at all. If you find that other compilers can handle your code and Clang
>> cannot, maybe Clang is wrong (in which you should fill a bug), or maybe the
>> other compiler is wrong at accepting your code, (in which you should file a
>> bug in the other compiler). However, if the error is the same (which it is
>> in GCC), than there's little you can ask the Clang community to do
>> something.
>>
>> As for learning C++, I suggest you buy Stroustroup's "The C++ Programming
>> Language", read it cover to cover, and have it as your faithful companion
>> for such cases, or use comp.lang.c++ for when you can't find the answer
>> yourself, but Clang's list is really not the place for that level of
>> discussion.
>>
>> cheers,
>> --renato
>>
>
>
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