Linker error, probably related to usage of GTSAM_EXPORT macro

[rafaelspring]

When building gtsam_points I get plenty of linker errors like this one:

isam2_ext.cpp.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) public: static void __cdecl
gtsam_points::UpdateImpl::LogStartingUpdate(class gtsam::NonlinearFactorGraph const &,class gtsam_points::ISAM2Ext const &)"
(_imp?LogStartingUpdate@UpdateImpl@gtsam_points@@SAXAEBVNonlinearFactorGraph@gtsam@@AEBVISAM2Ext@2@@z) referenced in function "public: virtual struct gtsam_points::ISAM2ResultExt __cdecl gtsam_points::ISAM2Ext::update(class gtsam::NonlinearFactorGraph const &,class gtsam::Values const &,struct gtsam::ISAM2UpdateParams const &)" (?update@ISAM2Ext@gtsam_points@@UEAA?AUISAM2ResultExt@2@AEBVNonlinearFactorGraph@gtsam@@AEBVValues@5@AEBUISAM2UpdateParams@5@@z)

The errors go away when using add_definitions(-DGTSAM_EXPORTS) in CMakeLists.txt to set the GTSAM_EXPORT macro to __declspec(dllexport).

However, the problem is that gtsam_points depends on GTSAM and when its headers are included they as well have the GTSAM_EXPORTS macro active and therefore treat GTSAM's symbols as exported symbols! This causes other problems in the build.
So including GTSAM headers should be done under a regime of __declspec(dllimport) (not export!), as we're just using GTSAM as a library, not building it.

Therefore I think gtsam_points should have its own dllexport.h header file and use the definition GTSAM_POINTS_EXPORTS and macro name GTSAM_POINTS_EXPORT to avoid the confusion with the GTSAM macros.

I am building on Windows 10, x64.

[koide3]

Thanks for reporting the issue.
I agree with that we should have our own EXPORT macros. While I've been occupied with some works in next a few weeks, l try to add these macros to support build on windows in next month.