Build of dll library on windows

[Josko692]

Hello, I work on windows 10 with mingw64 tools (gcc, g++, mingw32-make).
When I passed to the v1.1.12 of JSBSim I decided to use the shared Library.
I use the CMakeLists.txt of the project. My cmake line is :

cmake .. -G"MinGW Makefiles" -DCMAKE_CXX_FLAGS_DEBUG="-g -Wall" -DCMAKE_C_FLAGS_DEBUG="-g -Wall" -DCMAKE_BUILD_TYPE=Debug -DBUILD_SHARED_LIBS=ON -DBUILD_PYTHON_MODULE=OFF -DCMAKE_INSTALL_PREFIX=../install

There is no problem with the compilation of the dll but when linking. Apparently there is a problem with the FGOutput files (in src/models/) and I can't link to get JSBSim.exe. The script stops on an error and does not go to the end.
Did anyone manage to compile/link the V1.1.12 version using the dll ?

I attach a capture with the errors. Thank you for your help.

[bcoconni]

@Josko692 I can reproduce the bug so I opened the issue #719.

[bcoconni]

I'll submit a PR shortly to fix this issue. Meanwhile, you should be able to succeed compiling the DLL with MinGW32 by adding JSBSIM_API to the class header in src/models/FGOutput.h:

diff --git a/src/models/FGOutput.h b/src/models/FGOutput.h
--- a/src/models/FGOutput.h
+++ b/src/models/FGOutput.h
@@ -122,7 +122,7 @@ CLASS DOCUMENTATION
 CLASS DECLARATION
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%*/

-class FGOutput : public FGModel
+class JSBSIM_API FGOutput : public FGModel
 {
 public:
   FGOutput(FGFDMExec*);

[Josko692]

Thank you for your answer and your reactivity. I hope that next time I will be able to find the solution and propose a pull request.

[seanmcleod]

Hmm, @bcoconni, @ImKogane, @jeffneosim, @gallonmate I wonder if this lack of JSBSIM_API for FGOutput, although not causing a linker issue with the Microsoft linker is possibly causing a runtime issue in terms of this report with regards to not being able to generate an output log file - #711 (comment)

[bcoconni]

Indeed, what puzzles me is that the DLL linkage succeeds for JSBSim.exe with MSVC even though JSBSIM_API is missing 😲. Actually, MSVC issues a whole lot of warning C4251 messages when compiling JSBSim as a DLL but nothing specifically related to FGOutput.

Microsoft docs mention that the purpose of warnings C2451 is "to minimize the possibility of data corruption when exporting a class declared as __declspec(dllexport)". So the next step might possibly be fixing the warnings C2451 ?!?

[gallonmate]

Nice thought/connection. I never tested UE5 logging until now. Though I can confirm output logging works without any changes related to this dll bug. For Unreal Engine logging, the aircraft xml file just needed to specify some folder location to work:
<output name="F:\Downloads\c172p\JSBout172C.csv" type="CSV" rate="60">

[seanmcleod]

@jeffneosim I moved your comment to the existing discussion #711 (comment) since there was nothing in the comment that was specific to this FGOutput issue plus there is an existing discussion that covers your comment.

[jeffneosim]

Thanks, This discussion is the one from my students, and I just write here it was faster for me….

[seanmcleod]

Sure it's faster for you, but it doesn't help anyone else looking into this specific issue with FGOutput now, or any other JSBSim users who in the future do a search for FGOutput issues etc.

[bcoconni]

@Josko692 The bug should now be fixed in the master branch (commit 9a63f2d).