[CMake] Why are object files built several times?

[Bill Hoffman]

Andreas Pakulat wrote:
> On 26.09.07 15:13:38, Dizzy wrote:
>   
>> On Wednesday 26 September 2007 14:55:52 Joachim Ziegler wrote:
>>     
>>> Hello,
>>>
>>> I have two targets that have nearly the same sources:
>>>
>>> ADD_EXECUTABLE(startCompletionServer StartCompletionServer.cpp
>>> ${BASEFILES}) ADD_EXECUTABLE(test-adler32 test-adler32.cpp ${BASEFILES})
>>>
>>> I wonder why every object file belonging to the BASEFILES is built
>>> twice, once for the first target, once again for the second. This
>>> doubles my compile time!?
>>>       
>> You will notice that cmake is building files inside a build directory 
>> different for each target. So it is ment to be that way (normally you may 
>> have different compile flags for different targets so you want that). If you 
>> do not want that then just put your BASEFILES in a "convenience library" and 
>> reuse it from both targets such as:
>>     
>
> Note that this creates a static convenience library which is not
> portable to some architectures without extra compiler flags (need -fPIC
> on amd64 and maybe other 64bit architectures).
>
> Another way is to create a shared lib (and also install that one), but
> don't provide headers for the library and don't give it a SOVERSION so
> people won't link against it.
>   
For the example given this is very portable.  He is building two 
executables and not two shared libraries.

-Bill