[CMake] simple project in Visual Studio 2008

[Jos.van.den.Oever at panalytical.com]

"Yuri V. Timenkov" <ytimenkov at parallels.com> wrote on 08/19/2008 03:26:34 
PM:

> On Tuesday 19 August 2008 17:10:56 Jos.van.den.Oever at panalytical.com 
wrote:
> > "Yuri V. Timenkov" <ytimenkov at parallels.com> wrote on 08/19/2008 
02:05:04
> >
> > PM:
> > > Are following posts solve your problem?
> > >
> > > http://www.cmake.org/pipermail/cmake/2008-July/023099.html
> > > http://www.cmake.org/pipermail/cmake/2006-September/011100.html
> > > http://www.cmake.org/pipermail/cmake/2005-February/006080.html
> >
> > Yes they do. The tricky point was having to know that the symbol
> > ${LIBRARYNAME}_EXPORTS is set when building the library.
> > Then adding something along these lines in the header file solves the
> > problem:
> >
> > #ifdef _WIN32
> > #  ifdef testc2_EXPORTS
> > #    define WHATEVER __declspec( dllexport )
> > #  else
> > #    define WHATEVER __declspec( dllimport )
> > #  endif
> > #else
> > #  define WHATEVER
> > #endif
> >
> > WHATEVER float LibC2Func();
> >
> > So now I can get a simple project with one dll and one exe to compile, 
but
> > I still do not understand which program determines whether the .exe 
should
> > link to a .lib or a .dll. Does the Microsoft Visual Studio compiler
> > determine this or does CMake inspect the header files?
> > I find it strange that the linking command depends on the contents of 
the
> > header files. Is there a reason for this?
> This is VS tricks. Studio generates 2 files: one import library (.
> lib) and one 
> - dynamic library (.dll). gcc (and mingw family) exports all symbols by 
> default, VS doesn't export anything by default. And if your dll doesn't 
> export anything, VS simply doesn't generate import library (for example, 
if 
> you generate resource-only dll). The only thing cmake knows is when you 
using 
> VS generator, library extension to link with -- is .lib. And when you 
use 
> __declspec( dllexport ), cl.exe puts special marks in objects indicating 
that 
> this symbol should be exported or imported. Also, VS can tell linker to 
add 
> some library, as it boost does with #pragma's.
> 
> Really, this is well-known issue for VS developers ("Where is my .lib 
file??? 
> >:-("), especially if you copy project and header files and forgot 
change 
> defines. But because CMake makes migration to windows very smooth, this 
> question appears near every month in this list as cmake on VS/Windows 
newbie 
> question.

Perhaps it's a idea to add an entry to http://www.cmake.org/Wiki/CMake_FAQ 
then.
Something that says: If there is no __declspec( dllexport ) in your 
header, only a dll and no lib is generated.
CMake only tells the linker about the .lib, so if __declspec( dllexport ) 
is not there linking fails even though there is a .dll file.

Thanks,
Jos 
 
  
Jos van den Oever - SW Engineering 
 
PANalytical 
Lelyweg 1 
7602 EA Almelo 
The Netherlands 
T   +31 (0)546 528
F   +31 (0)546 534598
Jos.van.den.Oever at panalytical.com
www.PANalytical.com


 PANalytical
The Analytical X-ray Company  

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