[CMake] How to let the user select the compiler and compiler flags.

[David Cole]

Do use CACHE with your set statements to put them in the cache, and then use the -C command line argument to prime the cache with your file, rather than including it in your CMakeLists file.

That should have the effect you're seeking...

HTH,
David C.


On Apr 1, 2013, at 3:54 AM, Daniel Carrera <dcarrera at gmail.com> wrote:

> Hi all,
> 
> I am just getting started with CMake. Here is my question: Is there a
> good way to have an external config file that specifies both the
> compiler an compile flags?
> 
> The program is compiled many times, and it makes sense to have the
> compiler and flags in a config file rather than have them in the
> command line. I am hoping to use CMake itself as the language of the
> config file. For example:
> 
> # -----   myprogram.cmake -----
> # Local configuration file.
> 
> set (CMAKE_Fortran_COMPILER      "mpif90")
> set (CMAKE_Fortran_FLAGS         "-fdefault-real-8")
> set (CMAKE_Fortran_FLAGS_DEBUG   "-O0 -g -fbounds-check")
> set (CMAKE_Fortran_FLAGS_RELEASE "-O3")
> set (CMAKE_BUILD_TYPE             RELEASE)
> 
> 
> I think this would be a useful config file and I can just "include" it
> in CMakeLists.txt. The problem is that the compiler must be specified
> before I run project(), while the compile flags must be specified
> AFTER project():
> 
> 
> cmake_minimum_required (VERSION 2.8)
> include ("path/to/myprogram.cmake")
> enable_language (Fortran)
> project (MyProgram)
> 
> 
> At this point all the compile flags have been overwritten by
> enable_language() and project().  Can anyone suggest a good solution?
> I have a few ideas, but I am not sure about them:
> 
> 1) I could give up on the idea of using CMake in the config file. The
> config file could be a shell script that sets some environment
> variables. My understanding is that this will work, but you would lose
> the flexibility of CMake.
> 
> 2) I could load the config file twice. Once before, and once after
> project(). I am not sure if this would have any unexpected
> side-effects.
> 
> 3) I could store the flags in the cache. But I am not sure if
> overwriting the cache is a good idea or not.
> 
> 4) I could use a shell script to split the config file into the
> compiler part and everything else, and then load them separately. I
> think I like this option, but I am not fully aware of the
> side-effects.
> 
> Does anyone have any words of advice or wisdom to share with me?
> 
> Cheers,
> Daniel.
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