How to set warning level in CMake?

Question

How to set the warning level for a project (not the whole solution) using CMake? Should work on Visual Studio and GCC.

I found various options but most seem either not to work or are not consistent with the documentation.

Answer 1

In modern CMake, the following works well:

if(MSVC)
  target_compile_options(${TARGET_NAME} PRIVATE /W4 /WX)
else()
  target_compile_options(${TARGET_NAME} PRIVATE -Wall -Wextra -Wpedantic -Werror)
endif()

My colleague suggested an alternative version:

target_compile_options(${TARGET_NAME} PRIVATE
  $<$<CXX_COMPILER_ID:MSVC>:/W4 /WX>
  $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wall -Wextra -Wpedantic -Werror>
)

Replace ${TARGET_NAME} with the actual target name. -Werror is optional, it turns all warnings into errors.

Or use add_compile_options(...) if you want to apply it to all targets as suggested by @aldo in the comments.

Also, be sure to understand the difference between PRIVATE and PUBLIC (public options will be inherited by targets that depend on the given target).