Problems using reference include Headers on C++ project.

[Antonio Castellon - RAC]

Wow, I spend too much time to refactoring the code, but it not compile
fine. :-( it's not easy to modify the problem with the typedef structs
definition...or perhaps i'm wrong and it is more easy than I found....
could you check if it is more complicated? if not, I will forced to search
to another library to be used on my project :-(

thanks for all
toni

On Thu, Oct 27, 2011 at 06:25, Antonio Castellon - RAC <
antonio.castellon.rac at gmail.com> wrote:

> Dear Jan,
>
> First of all, thanks for your answers. I don't want to evaluate if C is
> better than C++, on my particular case, I have need to integrate the libzdb
> into a framework of C++. Perhaps If you are interested (and if it is
> possible), I could modify the headers of this API according to C++
> compatibility and send to the packet in order that you include (not
> substitute) this new header files as a complement for future users that has
> the same problem than me.
> Very thanks for your support,
> Best regards
> Toni
>
>
> On Thu, Oct 27, 2011 at 03:10, Jan-Henrik Haukeland <hauk at tildeslash.com>wrote:
>
>> On Oct 26, 2011, at 5:56 PM, Antonio Castellon - RAC wrote:
>>
>> Interesting. This has nothing to do with extern "C" which I mentioned
>> earlier, though extern "C" should be added to libzdb headers if to be used
>> from C++.
>>
>> Out of curiosity I tested this and got the same error:
>>
>> > /usr/local/include/zdb/URL.h:55: error: conflicting declaration
>> ‘typedef struct URL_T* URL_T’
>> > /usr/local/include/zdb/URL.h:55: error: ‘struct URL_T’ has a previous
>> declaration as ‘struct URL_T’
>>
>> It seems that the problem has to do with forward declaration and
>> namespaces in C vs C++. In C, structs are in a separate namespace so it is
>> perfectly legal to forward declare and typedef a struct to a type of the
>> same name. That is;
>>
>> typedef struct URL_T *URL_T;
>>
>> But this does not work in C++ (as far as I understand, I'm no C++ guy
>> though). In C++ a struct is (basically) the same as a class, so typedef
>> *URL_T is in the same namespace as struct URL_T, hence the curious compiler
>> error "‘struct URL_T’ has a previous declaration as ‘struct URL_T’". The
>> "workaround" is simple; just give the two types different names. For
>> instance lowercase the struct name:
>>
>> typedef struct url_t *URL_T;
>>
>> Since we use this typedef forward declaration idiom to declare all API
>> objects in libzdb you would have to modify all the 5-6 API header files and
>> corresponding source code where the type is declared, if you still want to
>> use libzdb from C++. It is a question of modifying only 5 lines or so.
>> Though I'm not inclined to do the change in the repository since this just
>> demonstrated how C is superior to C++ (Obviously I'm a C guy :)
>>
>> Best
>>
>> --
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>>
>
>
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