Link fails

[stolk]

The linking fails with an endless spew of "multiple definition" for symbols in the header files.

Is it missing 'extern' keywords?

make -C SRC all
make[1]: Entering directory '/home/bram/src/VSR-LKH/SRC'
make LKH
make[2]: Entering directory '/home/bram/src/VSR-LKH/SRC'
cc -o ../LKH OBJ/Activate.o OBJ/AddCandidate.o OBJ/AddExtraCandidates.o OBJ/AddTourCandidates.o OBJ/AdjustCandidateSet.o OBJ/AdjustClusters.o OBJ/AllocateStructures.o OBJ/Ascent.o OBJ/Best2OptMove.o OBJ/Best3OptMove.o OBJ/Best4OptMove.o OBJ/Best5OptMove.o OBJ/BestKOptMove.o OBJ/Between.o OBJ/Between_SL.o OBJ/Between_SSL.o OBJ/BridgeGain.o OBJ/BuildKDTree.o OBJ/C.o OBJ/CandidateReport.o OBJ/ChooseInitialTour.o OBJ/Connect.o OBJ/CreateCandidateSet.o OBJ/CreateDelaunayCandidateSet.o OBJ/CreateNNCandidateSet.o OBJ/Create_POPMUSIC_CandidateSet.o OBJ/CreateQuadrantCandidateSet.o OBJ/Delaunay.o OBJ/Distance.o OBJ/Distance_SPECIAL.o OBJ/eprintf.o OBJ/ERXT.o OBJ/Excludable.o OBJ/Exclude.o OBJ/FindTour.o OBJ/FixedOrCommonCandidates.o OBJ/Flip.o OBJ/Flip_SL.o OBJ/Flip_SSL.o OBJ/Forbidden.o OBJ/FreeStructures.o OBJ/fscanint.o OBJ/Gain23.o OBJ/GenerateCandidates.o OBJ/Genetic.o OBJ/GeoConversion.o OBJ/GetTime.o OBJ/GreedyTour.o OBJ/Hashing.o OBJ/Heap.o OBJ/IsBackboneCandidate.o OBJ/IsCandidate.o OBJ/IsCommonEdge.o OBJ/IsPossibleCandidate.o OBJ/KSwapKick.o OBJ/LinKernighan.o OBJ/LKHmain.o OBJ/Make2OptMove.o OBJ/Make3OptMove.o OBJ/Make4OptMove.o OBJ/Make5OptMove.o OBJ/MakeKOptMove.o OBJ/MergeTourWithBestTour.o OBJ/MergeWithTourIPT.o OBJ/Minimum1TreeCost.o OBJ/MinimumSpanningTree.o OBJ/NormalizeNodeList.o OBJ/NormalizeSegmentList.o OBJ/OrderCandidateSet.o OBJ/PatchCycles.o OBJ/printff.o OBJ/PrintParameters.o OBJ/Random.o OBJ/ReadCandidates.o OBJ/ReadEdges.o OBJ/ReadLine.o OBJ/ReadParameters.o OBJ/ReadPenalties.o OBJ/ReadProblem.o OBJ/RecordBestTour.o OBJ/RecordBetterTour.o OBJ/RemoveFirstActive.o OBJ/ResetCandidateSet.o OBJ/RestoreTour.o OBJ/SegmentSize.o OBJ/Sequence.o OBJ/SFCTour.o OBJ/SolveCompressedSubproblem.o OBJ/SolveDelaunaySubproblems.o OBJ/SolveKarpSubproblems.o OBJ/SolveKCenterSubproblems.o OBJ/SolveKMeansSubproblems.o OBJ/SolveRoheSubproblems.o OBJ/SolveSFCSubproblems.o OBJ/SolveSubproblem.o OBJ/SolveSubproblemBorderProblems.o OBJ/SolveTourSegmentSubproblems.o OBJ/Statistics.o OBJ/StoreTour.o OBJ/SymmetrizeCandidateSet.o OBJ/TrimCandidateSet.o OBJ/WriteCandidates.o OBJ/WritePenalties.o OBJ/WriteTour.o OBJ/MergeWithTourGPX2.o OBJ/gpx.o -O3 -Wall -IINCLUDE -DTWO_LEVEL_TREE -g -lm
/usr/bin/ld: OBJ/AddCandidate.o:/home/bram/src/VSR-LKH/SRC/INCLUDE/LKH.h:207: multiple definition of `FirstNode'; OBJ/Activate.o:/home/bram/src/VSR-LKH/SRC/INCLUDE/LKH.h:207: first defined here

This is on Ubuntu 20.10

[LongWang7]

because the version of gcc is not matched with Ununtu.
the solution you can add extern one by one,or degrade the version of gcc to 9
after doing this,the code could be implemented.