[CMake] novice question: modification of FLAGS rule variable?

[David Dunkle]

Thanks, Glenn. That almost works. However, the values of <FLAGS> is hard to construct in this case. It looks something like this:

add_library(mylib, STATIC, ${files})
set_target_properties(mylib
                                      PROPERTIES PREFIX ""
                                      COMPILE_FLAGS ${target_compiler_flags})
add_library(mylibd, STATIC, ${files})
set_target_properties(mylibd,
                                      PROPERTIES PREFIX ""
                                      COMPILE_FLAGS "-DDEBUG ${target_compiler_flags}")
...
set(CMAKE_C_COMPILE_OBJECT "${target_compiler} -c <FLAGS> -o <OBJECT>")

I can replace <FLAGS> with ${target_compiler_flags} yielding this:

set(CMAKE_C_COMPILE_OBJECT "${target_compiler} -c ${target_compiler_flags} -o <OBJECT>")

but then the -DDEBUG is missing for the build of mylibd. I guess both mylibd and mylib use CMAKE_C_COMPILE_OBJECT and I need a way to pass the -DDEBUG to the compile of one and not the other.

-David

From: Glenn Coombs [mailto:glenn.coombs at gmail.com]
Sent: Wednesday, September 07, 2011 4:19 AM
To: David Cole
Cc: David Dunkle; cmake at cmake.org
Subject: Re: [CMake] novice question: modification of FLAGS rule variable?

What you can do however is set the variable which uses the <FLAGS> definition, i.e. CMAKE_C_COMPILE_OBJECT in your example.  I have a CMakeLists.txt file where I override the default assembler flags:

set(CMAKE_ASM-ATT_COMPILE_OBJECT "<CMAKE_ASM-ATT_COMPILER> ${ASM_SYS_FLAGS} -o <OBJECT> <SOURCE>")

to use what is set in my ASM_SYS_FLAGS variable instead of the default <FLAGS> one.  I'm not sure but I think you are supposed to set these sort of variables early on in a CMakeList.txt before the project() or enable_language() commands.  Also, I think that later changes to the ASM_SYS_FLAGS variable are ignored.

--
Glenn
On 5 September 2011 19:53, David Cole <david.cole at kitware.com<mailto:david.cole at kitware.com>> wrote:
On Mon, Sep 5, 2011 at 1:31 PM, David Dunkle <ddunkle at arxan.com<mailto:ddunkle at arxan.com>> wrote:
> Is it possible to read and to set a property/rule variable like <FLAGS>?
> What syntax would I use to do that? I mean <FLAGS> as it, for example,
> appears here:
>
>
>
> set(CMAKE_C_COMPILE_OBJECT "${target_compiler} -c <FLAGS> -o <OBJECT>")
>
>
>
> For example can I do something like this (this is pseudo code)?
>
>
>
> #read
>
> set(MY_FLAGS,  ${<FLAGS>} );
>
>
>
> ...
>
>
>
> #set
>
> set(<FLAGS>, ${MY_FLAGS});
>
>
>
> In the documentation, here:
>
>
>
> http://cmake.org/Wiki/CMake_Useful_Variables#Expansion_Rules
>
>
>
> it hints at this being possible but doesn't explain, at least not so that I
> understand.
>
>
>
> Thanks,
>
> -David
>
>
>
>
>
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The wiki page is simply misleading. You cannot set those from the
CMake language. CMake decides on their values in internal code, and
then substitutes appropriately when generating make files or
solution/project files for the build system.

You can set things the "CMAKE_CXX_FLAGS" which eventually get
translated into the substitution that CMake performs, but you cannot
alter "<FLAGS>" in the rules variables.


HTH,
David
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