[CMake] Newbie question: Static linking

[Sanatan Rai]

On 23 May 2011 15:11, Michael Wild <themiwi at gmail.com> wrote:
>>> Yes, but you are registering the concrete factories implicitly instead
>>> of explicitly, which is causing you the trouble you experience.
>>>
>>> Better have your user provide a function registering his/her classes
>>> explicitly.
>>
>> I guess this is getting to be off topic, but indeed the
>> anonymous namespace trick is supposed to do exactly that.
<snipped>
>> libraries that this problem occurs. I haven't seen a solution to this
>> problem either in books or via google.
>>
>> --Sanatan
>
> The problem is, that when you link a static library to another binary
> (be it shared library or executable) only the *required* symbols are
> used, all others get discarded. Since nothing in your code actually
> references those global instances in the anonymous namespace (the linker
> doesn't care about that, BTW), they are ignored.
>
> Four solutions:
>
> 1. Only do monolithic builds.
> 2. Use shared libraries/DLLs
> 3. Use --whole-archive or similar and hack your way through MSVC (I did
> it once. It was ugly. Very ugly. See
> https://github.com/themiwi/cppcheck/tree/227378f763d50b005b7dd2167e2cef791054a30c.
> Especially lib/CMakeLists.txt and lib/generateStaticLinkFlags.cmake. I
> replaced it with an explicit registration scheme now...)
> 4. Use an explicit registration scheme.
>
> For sanity's sake, go with 4.

   Ok: you've lost me here. Are you saying a trick like:

   namespace {
     helper1 *createHelper1() { return (new Helper1());}
     const bool isRegistered =
factory::instance().registerHelper("helper1", createHelper1);
}
isn't explicit?

I could do the following: create a global object in the cpp, that
belongs to a type that would
do the registration. Would you regard this also as implicit?

The problem with either of these approaches is the same: if the code
lives in a separate library
that is loaded only when needed, then these registrations don't take
place. So the framework doesn't
know that the objects can be available.

Apologies for seeming obtuse but I don't follow what you mean by
`explicit registration' here.

--Sanatan