[CMake] Order of operations in CMakeLists.txt file?

[Hendrik Sattler]

Am Freitag 18 Dezember 2009 19:34:12 schrieb Eric LaFranchi:
> > use
> >    project(test NONE)
> > to not enable any language. Then CMAKE_SYSTEM_NAME should be defined.
> > OTOH, you may want to think again about your approach of doing things.  
> > It makes it impossible to change compilers on a platform without  
> > changing the CMakeList.txt file. What exactly is your use-case for the  
> > above stuff?
> >
> > HS
> 
> We build on multiple platforms and some of the platforms have more than
> one C/C++ compiler installed. In the CMakeLists.txt we set the compiler
> and flags for each platform by switching on the platform based on
> CMAKE_SYSTEM_NAME. Can you suggest other mechanisms for doing this type
> of operation?

You have several options:
1.
before calling cmake, include a set of environment variables that are 
recognized by cmake to configure for that toolchain. This can be the same name 
on each architecture, e.g.:
  export CC=cc1
  export CPPFLAGS=-DFOO_X
  export CFLAGS=-cc1flag_a

  bash$ source /some/path/default-toolchain.sh
  bash$ cmake ../myproject

2.
use a toolchain specific wrapper for cmake. Like for (1), this  script can have 
the same name on each platform, e.g.
  #!/bin/sh
  exec cmake -DCMAKE_C_COMPILER=cc1 "$@"

3.
a combination of (1) and (2)

The good thing: (1) is already the default use case of cmake when using 
MSVC7/8/9/10. Additionally, keeping this information out of the CMakeLists.txt 
scales better, especially when you want to use different compilers for one 
platform. The flags to make the software compile for a specific compiler or 
platform still belongs to the CMakeLists.txt, though.

HS