cmake - Set CXX-standard to c++17 when combining C++ and CUDA in CMakeLists

Question

According to the documentation of CMake I just have to write

project(${PROJECT_NAME} LANGUAGES CUDA CXX)

when I would like to combine CUDA-files and native C++-files in one project. Then I do not have to call cuda_add_executable() anymore, but rather add_executable, and CMake should figure out everything on its own. This works fine, unless I would like to specify a standard for C++-code (by using set(CMAKE_CXX_STANDARD 17)). Then I get the error message

Target requires the language dialect "CUDA17" (with compiler extensions), but CMake does not know the compile flags to use to enable it

Is there an alternative solution, or should I rather revert to find_package(CUDA) and cuda_add_executable?

Answer 1

Based on the comment from @talonmies I found a solution for that problem by setting the variables explicitly for each language, i.e. CUDA and CXX:

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CUDA_STANDARD 14)
set(CMAKE_CUDA_STANDARD_REQUIRED TRUE)
set(CMAKE_CXX_STANDARD_REQUIRED TRUE)

Now the pure C++-files are compiled according to C++17, and the CUDA-files are compiled according to C++14.