Compiling DCMTK with C++11/14/17 Features with MSVC

[nbeck]

Hello,
I managed to compile the toolkit with Visual Studio 2022. However, I noticed that CMake disabled the features of newer C++ versions:

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Checking whether the compiler supports C++11
Checking whether the compiler supports C++11 -- no
Info: C++11 features disabled
Info: C++14 features disabled
Info: C++17 features disabled

I tried setting the variable CMAKE_CXX_STANDARD = 17 as mentioned in the INSTALL document, but that didn't seem to change anything. Is this a problem with the Visual Studio compiler or am I missing something?

[nbeck]

After some digging I found that the problem occurs in dcmtk\config\tests\cxx11.cc. The code checks for the macro __cplusplus:

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#elif __cplusplus < 201103L

#error "This is not a C++11 compiler"

Unfortunately, MSVC doesn't set this macro correctly. From https://learn.microsoft.com/en-us/cpp/b ... w=msvc-170:
... Because a lot of existing code appears to depend on the value of this macro matching 199711L, the compiler doesn't change the value of the macro unless you explicitly opt in by using the /Zc:__cplusplus compiler option.

I changed line 1453 in the function DCMTK_CHECK_CXX_STANDARD in dcmtk\CMake\GenerateDCMTKConfigure.cmake to

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try_compile(COMPILE_RESULT "${CMAKE_BINARY_DIR}" "${DCMTK_SOURCE_DIR}/config/tests/cxx${STANDARD}.cc" COMPILE_DEFINITIONS  "/Zc:__cplusplus")

CMake now enables the C++ features:

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Info: C++11 features enabled
Info: C++14 features enabled
Info: C++17 features enabled

I also added the following to dcmtk\CMakeLists.txt

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set(CMAKE_CXX_STANDARD 17)
if(MSVC)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} /Zc:__cplusplus")
endif()

However, the resulting VS solution is configured to use the C++14 standard, and I had to add /Zc:__cplusplus to the compiler flags for each project.

Is there a way to tell CMake to generate the solution with this compiler flag?

[nbeck]

I noticed that you have created a ticket for this issue: https://support.dcmtk.org/redmine/issues/1047.

Thanks for your work!

[Michael Onken]

Hi,

this has been fixed with commit 8f7de4df9 which should show up on public DCMTK master branch within a few days (after successfully passing various nightly builds).
Thank you for your report and suggested fix

Best regards,
Michael