Re: [boost] [CMake proto]howto use variadic compiler (was converted test directories?

From: Larry Evans (cppljevans_at_[hidden])
Date: 2007-08-16 16:42:02

On 08/16/2007 01:42 PM, Maik Beckmann wrote:
> Am Donnerstag, 16. August 2007 20:10:48 schrieb Larry Evans:
>> I tried this by creating a top-level build directory, built-by, with
>> subdirectories:
>>
>>    g++-4.1    #the "regular" compiler
>>    g++-4.3_v  #the "variadic" compiler
>>
>> For 4.3_v, I had to first do `cmake <path-to-source>` then edit the
>> g++-4.3_v/CMakeCache.txt to include the lines:
>>
>> //CXX compiler.
>> CMAKE_CXX_COMPILER:FILEPATH=/home/evansl/download/gcc/variadic-templates/gc
>> c-4.3-20070323/install/bin/g++
>>
>> //Flags used by the compiler during all build types.
>> CMAKE_CXX_FLAGS:STRING=-std=gnu++0x
>>
>> The FLAGS value was needed, as you know, to enable variadic templates.
>>
>> However, after I tried `make` the value of COMPILER:FILEPATH was
>> reverted back to /usr/bin/g++ by something.  How can that reversion be
>> prevented or is there a better way to cause the variadic compiler to be
>> used?
> 
> Hello Larry,
> 
> If you want to say CMake which compiler it has to use,  you must give it via 
> the matching environment variable (CXX for the c++ compiler, CC for c, FC for 
> fortran) like:
>     $ cd /path/to/builddir
>     $ CXX=/home/evansl/download/gcc/variadic-templates\
>                 /gcc-4.3-20070323/install/bin/g++ \
>           cmake /path/to/boost-cmake

Or, a more descriptive name than /path/to/boost-cmake would be
$BOOST/src, which is what's used on:

http://svn.boost.org/trac/boost/wiki/CMakeConfigAndBuild

> 
> 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?

> This behavior of CMake ensures that the results of the test CMake runs on the 
> compiler are allway valid. Since the results are stored in CMakeLists.txt, 

Which CMakeLists.txt?  The following command:

cd ~/prog_dev/boost-svn/ro/sandbox-branches/boost-cmake/src/
find . -name CMakeLists.txt -ls
5181833   12 -rw-r--r--   1 evansl   evansl      10169 Aug 13 16:16 
./libs/config/test/CMakeLists.txt
...

shows no times later than yesterday; hence, it's unclear to me what
'results are stored in CMakeLists.txt' means.  Could you please clarify?

> you have to remove it, which triggers CMake to rerun the compiler tests.

Does 'it' refer to CMakeLists.txt or CMakeCache.txt?

> 
> Regards, Maik Beckmann

Thanks for the feedback!

-regards,
Larry