On 08/17/2007 07:47 AM, Douglas Gregor wrote:
Larry Evans wrote:
Note: you have to remove CMakeCache.txt, if it exists.
OK, so, in order to emulate Boost.Build's command line interface as close as possible, the user would create a bash (or whatever shell) file which has the one line:
CXX=/home/evansl/download/gcc/variadic-templates\ /gcc-4.3-20070323/install/bin/g++ \ cmake $BOOST/src
The only reason for this, which in this case is important, is to save repeatedly typing the long command between source code edits and testing. I assume the CMAKE_CXX_FLAGS:STRING value from the CMakeCache.txt is used since I saw the error message when make was run:
Scanning dependencies of target boost_iostreams-shared [ 2%] Building CXX object libs/iostreams/src/CMakeFiles/boost_iostreams-shared.dir/file_descriptor.o cc1plus: error: unrecognized command line option "-std=gnu++0x" make[2]: *** [libs/iostreams/src/CMakeFiles/boost_iostreams-shared.dir/file_descriptor.o]
This is inconsistent because the FLAGS value is used from CMakeCache.txt, but the CXX_COMPILER is ignored and even overwritten. Why put the CXX_COMPILER assignment in the CMakeCache.txt file if it's ignored?
It seems like there's a bit of a misunderstanding about the way CMake actual works that is causing a lot of confusion.
The "cmake" program (and its more graphical cousin, "ccmake") generates makefiles. You should only need to run "cmake" or "ccmake" once, to configure your source tree. That execution creates the appropriate makefiles, and you use your normal platform build tool (say, "make") from there on. The only reason to re-run "cmake" is if you've changed options, by editing CMakeCache.txt directly.
Doug, I did understand that cmake generates Makefiles; however, I thought editing the CMakeCache.txt file to change the compiler *then* running cmake would use the new compiler when generating the Makefile. But that's apparently wrong. Whenever I did that (edit CMakeCache.txt; run cmake) the CMakeCache.txt file value for the compiler was changed *back* to the value before the manual edit. As Maik indicated, the only way to get a new value for the compiler was with the command line invokation of cmake. The following shows the contents of the bash script file I used to do this: cd ~/prog_dev/boost-svn/ro/sandbox-branches/boost-cmake/built-by/g++-4.3_v/ cat CMake.sh #!/bin/bash CXX=/home/evansl/download/gcc/variadic-templates\ /gcc-4.3-20070323/install/bin/g++ \ cmake ../../src Compilation finished at Fri Aug 17 08:38:11 What's confusing is when ccmake is used and expert mode is turned on, the value for CMAKE_CXX_COMPILER is shown, but changing that, just like manually editing the CMakeCache.txt file to change it. has no effect. That's not very intuitive.
Personally, here's how I use CMake: I create a new build directory, and run "ccmake /path/to/boost" from that directory. In that interface, I set the options I'm interested in, (c)onfigure until they're stable, and (g)enerate makefiles. It is very, very, very rare that I actually need to run "cmake" or "ccmake" again after that, because calling "make" automatically keeps everything else in sync.
I tried that (at least I pretty sure that's what I did); yet, the CXX compiler was not retained when I ran cmake.