[CMake] Newbie question: Static linking

[Michael Wild]

On 05/23/2011 03:25 PM, Sanatan Rai wrote:
> On 23 May 2011 13:38, Michael Wild <themiwi at gmail.com> wrote:
>> On 05/23/2011 02:20 PM, Sanatan Rai wrote:
>>> On 23 May 2011 12:54, Michael Jackson <mike.jackson at bluequartz.net> wrote:
>>>> You might want to take a look at the Factory design pattern.
>>>>
>>>
>>> That's exactly what I use...
>>>
>>> --Sanatan
>>
>> 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.
> 
> I am not trying to be difficult here---just that it is not clear to me
> that the solution to this problem is that straightforward.
> 
> When all the code files are linked in one monolithic bloc, everything
> works correctly. It is when one starts dividing them into individual
> 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.

Michael