Using CMake with multiple compilers for the same language

It seems like CMake is fairly entrenched in its view that there should be one, and only one, CMAKE_CXX_COMPILER for all C++ source files. I can't find a way to override this on a per-target basis. This makes a mix of host-and-cross compiling in a single CMakeLists.txt very difficult with the built-in CMake facilities.

So, my question is: what's the best way to use multiple compilers for the same language (i.e. C++)?

It's impossible to do this with CMake.

CMake only keeps one set of compiler properties which is shared by all targets in a CMakeLists.txt file. If you want to use two compilers, you need to run CMake twice. This is even true for e.g. building 32bit and 64bit binaries from the same compiler toolchain.

The quick-and-dirty way around this is using custom commands. But then you end up with what are basically glorified shell-scripts, which is probably not what you want.

The clean solution is: Don't put them in the same CMakeLists.txt! You can't link between different architectures anyway, so there is no need for them to be in the same file. You may reduce redundancies by refactoring common parts of the CMake scripts into separate files and include() them.

The main disadvantage here is that you lose the ability to build with a single command, but you can solve that by writing a wrapper in your favorite scripting language that takes care of calling the different CMake-makefiles.

You might want to look at ExternalProject: http://www.kitware.com/media/html/BuildingExternalProjectsWithCMake2.8.html