Re: [Boost-build] Future development

From: Larry Evans (cppljevans_at_[hidden])
Date: 2007-10-12 16:33:26

On 10/12/07 13:54, Bill Hoffman wrote:
 > Larry Evans wrote:
 >> On 10/05/07 16:17, David Abrahams wrote:
 >>  > on Fri Oct 05 2007, Larry Evans <cppljevans-AT-cox-internet.com> 
wrote:
 >>  >
 >>  >> Dave, because I was having trouble with BB, I tried CMake briefly
 >>  >> around August.  It was hard to specify a different compiler, as
 >>  >> described here:
 >>  >>
 >>  >> http://lists.boost.org/Archives/boost/2007/08/126117.php
 >>  >>
 >>  >> I guess this qualifies as "empirical data".
 >>  >
 >>  > Yes, it does, thanks.
 >>  >
 >>  >> After that CMake experience, I went back to BB to see if I could
 >>  >> understand it (in particular the extending) better.  I'm still
 >>  >> trying :(.
 >>
 >> BTW, I've made some progress in getting BB to work on the problem,
 >> which was emulating the GMCPPOT (see below).
 >>
 > OK, so that was a very long email.   :-)

Sorry.  I probably sould have shortened it, but it took me so long to
write :(, I just didn't have the heart to shorten it.

 >
 > Can we sum it up into the following three issues?
 >
 > 1. Once you configure a binary tree for a build with CMake,
 > it is not easy to change the compiler.

Yep.

 >
 > 2. You want to pass flags to the compiler like -E, but cmake does not
 > allow this.

I didn't mean this.  The mention of using -E was only meant to show I
used it to debug c++ macros, and that a similar feature would be
useful w.r.t. cmake macros.  Sorry I wasn't clear.  However, I tested
this, and indeed you're right.  I tried:

#!/bin/bash
cmake -DCMAKE_CXX_COMPILER=/home/evansl/download/gcc/\
4.3-20071005/install/bin/g++\
   -std=gnu++0x\
   -I/home/evansl/prog_dev/boost-cvs/ro/boost/sandbox/variadic-templates\
   ../../src

and the resulting CMakeCache.txt didn't have the -std or the -I flags:

//CXX compiler.
CMAKE_CXX_COMPILER:FILEPATH=/home/evansl/download/gcc/4.3-20071005/install/bin/g++

This is needed in order to test the variadic compiler.  The -std flag
signals variadic templates and the -I is to include my variadic boost
directory ahead of the normal boost directory.  So, unless there's a
workaround, I think this is a definite negative on cmake's side of the
comparison with BB.  With BB, in my user-config.jam, I just have this:

using gcc
   : 4.3_v
   : 
"/home/evansl/download/gcc/variadic-templates/gcc-4.3-20070323/install/bin/g++" 

   : 
<cxxflags>-I/home/evansl/prog_dev/boost-cvs/ro/boost/sandbox/variadic-templates 

     <cxxflags>-std=gnu++0x
   ;

and then just say `bjam --toolset=gcc-4.3_v` to get this compiler with
these flags.

 >
 > 3. You want some sort of mapping between the CMakeLists.txt input files
 > and the
 > generated Makefiles.

Yes.  However, I've had no real experience and it may not be that
necessary.  I was just extrapolating my experience with c++ macros.

 > To answer those issues:
 >
 > 1. Yes, you can not change the compiler once cmake has run.
[snip]
 >
 > 2. make source.i will generate preprocessed output for a given compiler.
 > make help in a directory will show the possible targets to make.

Yes, that's what Brad mentioned here:

http://article.gmane.org/gmane.comp.lib.boost.build/16524

However, what I want is to filter the output through csplit and then
ident to it's more readable.

 >
 > 3. You are the first to make this request.   For each directory in the
 > source tree that has a CMakeLists.txt file, a directory in the binary
 > tree will be created.   The lines of the CMakeLists.txt file do
 > not directly map to any particular line of the Makefile.   I something
 > could be done here, but I am not sure how useful it would be.

You're probably right.  As I mentioned, it was an extrapolation of my
experience with cpp macros.  Since the output of cmake macro's is much
more user-readable and probably much easier to trace back to the
source, I withdraw the request.

Thanks for your response.

-Larry