Setting `CMAKE_CXX_FLAGS` within a function

Usage
1

It seems that CMAKE_CXX_FLAGS isn’t being set when I set it inside of a function. I tried checking the contents, it is empty before and after, even within the same function.

These are all things I’ve tried, neither work for me:

set(${CMAKE_CXX_FLAGS} "${CMAKE_CXX_FLAGS} ${val}")

set(${CMAKE_CXX_FLAGS} "${${CMAKE_CXX_FLAGS}} ${val}")

set(${CMAKE_CXX_FLAGS} "${${CMAKE_CXX_FLAGS}} ${val}" PARENT_SCOPE)
2

You are wrong. To set a variable, use just the variable name, do not expand it:

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${val}" PARENT_SCOPE)
3

Huh, when is the ${VAR} syntax used then?

4

When you pass variable name to a function:

function (UPDATE_MY_VAR my_var)
  set(${my_var} "my value" PARENT_SCOPE)
endfunction()

update_my_var(VAR_TO_UPDATE)
# here VAR_TO_UPDATE has value "my value"
5

Ah, okay. Also, is there a way of forwarding the scope of the variable above two or more functions?

6

No. You can only update variables of the parent scope.

7

Note that the better solution these days is something like:

add_library(buildflags INTERFACE)
target_compile_options(buildflags INTERFACE -Wsome-warning)

# For each target
target_link_libraries(mytgt PRIVATE buildflags)
8

@ben.boeckel You mean target_compile_options.

9

Indeed, thanks. I’ve updated the comment.