[CMake] Per Target CMAKE_C??_FLAGS Reset/Redefinition

[Murali Paluru]

Hi David,

The project that I am working on has similar needs of having different
flags for each target. I have placed the different targets in different
sub-folders and set the CMAKE_*_FLAGS. This approach seems to work fine as
you mentioned.

>From my understanding, a new add_subdirectory creates a new scope of
variables.

I feel that having different targets in different directories is a good
logical separation. So if that's working for you, why not use it? I am not
sure if there is a better way, but I hope someone will comment.

Regards,
Murali.

On Mon, May 25, 2015 at 1:04 PM, David Hauck <davidh at netacquire.com> wrote:

> Hi,
>
> I've been searching for a definitive discussion of this but haven't been
> successful finding it. I have a (Unix Makefile) CMakeLists.txt project
> sub-directory that defines several (3) targets (for executable and shared
> targets). I'm trying to reset/redefine the CMAKE_C??_FLAGS (specifically
> CMAKE_C_FLAGS) property on one of the targets via the following statement
> in the CMakeLists.txt file:
>
> set_property(TARGET <target_name> PROPERTY CMAKE_C_FLAGS "-Wall -shared")
> set_property(TARGET <target_name> PROPERTY CMAKE_C_FLAGS_DEBUG "-g")
> set_property(TARGET <target_name> PROPERTY CMAKE_C_FLAGS_RELEASE "-O3")
>
> However, this isn't working and the resulting target compilation is using
> the directory's value for these properties. Other redefinitions of
> per-target properties (e.g., INCLUDE_DIRECTORIES) do seem to take so I'm
> wondering if certain properties are per-directory only and aren't
> meaningful with the "set_property(TARGET ...)" construct?
>
> If I move the target to its own sub-directory and use the following
> CMakeLists.txt commands instead the compile flags are properly (re)set:
>
> SET (CMAKE_C_FLAGS "-Wall -shared")
> SET (CMAKE_C_FLAGS_DEBUG "-g")
> SET (CMAKE_C_FLAGS_RELEASE "-O3")
>
> Oddly the aforementioned "set_property(TARGET..." constructs in place of
> the above "SET(CMAKE..." constructs also fail to reset the flags in this
> new directory so this doesn't seem related to the sub-directory
> CMakeLists.txt file when multiple targets are defined.
>
> I must have missed something obvious related to this in the documentation
> and/or the mailing list/Google. Any ideas?
>
> Thanks,
> -David
>
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