MEX build issue on Windows

[fkg-ctsi]

Hi there!
Firstly, thank you so much for all of the continued development and support over the years. This project has really helped make this industry more accessible!

I have a (likely) noob question re: compiling the S-Function using MEX.

I've been following the guide, and when I get to the step to compile with mex, I get a large link error dump.

Here is a snippet:

Error using mex Creating library JSBSim_SFunction.lib and object JSBSim_SFunction.exp LINK : warning LNK4217: symbol '??0SGPath@@QEAA@P6A?AUPermissions@0@AEBV0@@Z@Z (public: __cdecl SGPath::SGPath(struct SGPath::Permissions (__cdecl*)(class SGPath const &)))' defined in 'JSBSim.lib(sg_path.obj)' is imported by 'JSBSim_SFunction.obj' in function '"void __cdecl mdlInitializeConditions(struct SimStruct_tag *)" (?mdlInitializeConditions@@YAXPEAUSimStruct_tag@@@Z)'
...
...
JSBSim_SFunction.mexw64 : fatal error LNK1120: 13 unresolved externals

For reference, I am using VS Community 2019, and Matlab/Simulink 2022b (Really hoping that this isn't the issue)

Admittedly, I am a MEX noob and only functional in C++, but would really appreciate a nudge in where to start investigating a path forwards.

Thanks!

[bcoconni]

Hi @fkg-ctsi, it looks very much like the script is trying to link with the JSBSim DLL although the static library has been built.

This should be fixed by providing the flag JSBSIM_STATIC_LINK to the mex command. For that purpose you need to update the script matlab/JSBSimSimulinkCompile.m like below (commenting out the Linux command -if not done yet- and adding JSBSIM_STATIC_LINK to the COMPFLAGS option of the Windows commmand):

diff --git a/matlab/JSBSimSimulinkCompile.m b/matlab/JSBSimSimulinkCompile.m
index e8004d90..61274dd5 100644
--- a/matlab/JSBSimSimulinkCompile.m
+++ b/matlab/JSBSimSimulinkCompile.m
@@ -1,8 +1,8 @@
 disp('Compiling S-function from JSBSim...');
 % For Linux: 
-mex -v -R2017b CXXFLAGS='$CXXFLAGS -std=c++14' ./matlab/JSBSim_SFunction.cpp ./matlab/JSBSimInterface.cpp -I./src -L./src/.libs -lJSBSim
+%mex -v -R2017b CXXFLAGS='$CXXFLAGS -std=c++14' ./matlab/JSBSim_SFunction.cpp ./matlab/JSBSimInterface.cpp -I./src -L./src/.libs -lJSBSim
 % For Windows:
-%mex -v -R2017b COMPFLAGS='$COMPFLAGS' ./matlab/JSBSim_SFunction.cpp ./matlab/JSBSimInterface.cpp -I".\out\install\x64-Release\include\JSBSim" -L".\out\install\x64-Release\lib" -lJSBSim  wsock32.lib ws2_32.lib
+mex -v -R2017b COMPFLAGS='$COMPFLAGS /DJSBSIM_STATIC_LINK' ./matlab/JSBSim_SFunction.cpp ./matlab/JSBSimInterface.cpp -I".\out\install\x64-Release\include\JSBSim" -L".\out\install\x64-Release\lib" -lJSBSim  wsock32.lib ws2_32.lib
 % For MacOS:
 %mex -v -R2017b CXXFLAGS='$CXXFLAGS -std=c++14' ./JSBSim_SFunction.cpp ./JSBSimInterface.cpp -I../src -L../build/src -lJSBSim
 disp('Finished.')

[fkg-ctsi]

@bcoconni got it running! Thank you so much!

[bcoconni]

Thanks for reporting the issue. I have created the PR #735 to fix the problem.