Compilation as VTK external module on Ubuntu 22.04

[kenavolic]

When compiling vtkDicom as external module of VTK (-DVTK_MODULE_ENABLE_VTK_vtkDICOM:STRING=WANT) on Ubuntu 22.04 with the system dcmtk there is a compilation issue:

/usr/include/dcmtk/config/osconfig.h:1144:2: error: invalid preprocessing directive #errorDCMTK
  #error\
      |  ^~~~~~
 DCMTK was configured to use C++17 features, but your compiler does not or was not configured to provide them.

The issue is due to no minimum standard requirement being set and is fixed by adding set(CMAKE_CXX_STANDARD 17) in the main vtkDicom CMakeLists.txt.

OS: Ubuntu 22.04 VTK: 9.2.5 with VTK_MODULE_ENABLE_VTK_vtkDICOM:STRING=WANT cmake: 3.24 system dcmtk: libdcmtk-dev/jammy,now 3.6.6-5 amd64

[dgobbi]

Thanks for the note. When you say "main CMakeLists.txt", you are referring to the VTK CMakeLists.txt? Or to the vtkDICOM CMakeLists.txt? Neither VTK or vtkDICOM is ready to set c++17 as an absolute requirement, so set(CMAKE_CXX_STANDARD 17) would have to be conditional on USE_DCMTK.

I might recommend using gdcm instead of dcmtk, which is what I use for the binary packages.

[kenavolic]

I edited my comment. As we don't install gdcm we rely on dcmtk backend for Dicom handling. A cleaner solution would be to update the Source/CMakelists.txt of vtkDicom with something like that (but better than that ;)):

if(USE_DCMTK)
  find_package(DCMTK)
  if(NOT DCMTK_FOUND)
    message(FATAL_ERROR "DCMTK not found or incomplete.")
  endif()
  foreach(_dcmtk_inc_dir ${DCMTK_INCLUDE_DIRS})
    if(EXISTS ${_dcmtk_inc_dir}/dcmtk/config/osconfig.h)
      file(READ ${_dcmtk_inc_dir}/dcmtk/config/osconfig.h _dcmtk_config)
      string(FIND "${_dcmtk_config}" "#define HAVE_CXX11 1" _cxx_11_std)
      string(FIND "${_dcmtk_config}" "#define HAVE_CXX14 1" _cxx_14_std)
      string(FIND "${_dcmtk_config}" "#define HAVE_CXX17 1" _cxx_17_std)
      if(NOT ${_cxx_17_std} EQUAL -1)
        set(CMAKE_CXX_STANDARD 17)
      elseif(NOT ${_cxx_17_std} EQUAL -1)
        set(CMAKE_CXX_STANDARD 14)
      elseif(NOT ${_cxx_11_std} EQUAL -1)
        set(CMAKE_CXX_STANDARD 11)
      endif()
    endif()  
  endforeach()
  if(${DCMTK_charls_LIBRARY})
    set(DCMTK_LIBS ${DCMTK_LIBRARIES} ${DCMTK_charls_LIBRARY})
  else()
    set(DCMTK_LIBS ${DCMTK_LIBRARIES})
  endif()
  if(APPLE)
    list(APPEND DCMTK_LIBS iconv)
  endif()
  include_directories(${DCMTK_INCLUDE_DIRS})
endif()

[dgobbi]

That looks like a reasonable solution (though a bit fragile because dcmtk might change its osconfig.h in the future). I can add that to the code after testing it on my own linux box.

In the meantime, adding -std=c++17 to CMAKE_CXX_FLAGS during the cmake configuration of VTK might work as a quick-and-dirty fix.

[dgobbi]

I've added 65ec1e7 to take care of this issue. Tomorrow I'll push a change to VTK to pick up this commit when it builds vtkDICOM as a remote module.

[kenavolic]

Much cleaner :) Thanks!

[mathstuf]

FindDCMTK should make this available through a variable. Better would be to put it on its exported targets. But this works in the meantime.

[dgobbi]

The vtk-dicom remote module for VTK 9.3 now has this fix. Closing.