[CMake] Weird DLL_EXPORT disables creation of .lib-files with Visual C++ .NET 2003

[Brad King]

wedekind wrote:
> I have created a CMakeLists.txt for a Visual C++ .NET 2003 project, I am
> using Cmake 2.0.6. My problem is, that the resulting vcproj-file does not
> create a .lib-file for the project, just the .dll-file is created. In order
> to link the created dll with my other projects I need the lib-file. No it
> gets weird... If I change a preprocessor definition from JCore_EXPORTS to
> JCORE_DLL_EXPORT (note the change in case too) it creates the lib file. But
> I doubt that changing this preprocessor definition alone is the solution
> because I also have (very similar) projects that create lib-files without
> this *_DLL_EXPORT-definition, they only have the cmake-created
> *_EXPORTS-definition (without DLL in it)!

When a dll is created it is up to the source code to put 
__declspec(dllexport) in the right places to tell the linker to export 
the symbols.  Those exports are then stored in the .lib file.  If there 
are no exports then no one can link to the library (it can only be 
loaded dynamically with a LoadLibrary call) so there is no reason to 
have a .lib file.

When a dll is used it is up to the source code to put 
__declspec(dllimport) in the right places to tell the linker that the 
symbol will come from a dll.  Since this has to be in the same place the 
typical solution is to use code like this:

#ifdef MYLIB_EXPORTS
# define MYLIB_EXPORT __declspec(dllexport)  /* building the lib */
#else
# define MYLIB_EXPORT __declspec(dllimport)  /* building user code */
#endif

Then the MYLIB_EXPORT macro is used in the right places in the source 
code.  In order to support this the build system must define 
"MYLIB_EXPORTS" when building the sources in the library and not define 
it elsewhere.  CMake provides automatic support for this by defining a 
"target-name_EXPORTS" macro for sources being placed in a shared library 
"target-name".

You will have to check that the code uses the same name for 
MYLIB_EXPORTS that CMake is defining.  If changing the code is not an 
option and it looks for a different macro than the one CMake provides 
you can tell CMake to provide a differnent one like this:

SET_TARGET_PROPERTIES(MYLIB PROPERTIES
   DEFINE_SYMBOL mylib_custom_EXPORTS_macro
)

-Brad