Re: [Boost-build] discovering libraries with boost at build time

Subject: Re: [Boost-build] discovering libraries with boost at build time
From: Vladimir Prus (ghost_at_[hidden])
Date: 2010-07-12 03:44:32

On Saturday 10 July 2010 12:52:39 John Maddock wrote:

> 
> > 2. I want the build system to detect if library is installed or missing. 
> > So I
> > can turn of building
> >   Boost.Locale or turn it on. Or just disable some features for other 
> > projects.
> >
> >   It is not so critical specifically for Boost.Locale, but if I was using 
> > BBv2
> > for my project like CppCMS
> >   that depends on 5-6 3rd part libraries, if I was asking a user to 
> > provide
> > flag for each one of them...
> >   I would have less users.
> 
> Are you sure we're looking at the same code here?
> 
> The new check-target-builds rule can in essence *do anything that autoconf 
> can*.
> 
> Consider the basic AC_TRY_COMPILE macro, to emulate this in Boost.Build we'd 
> start by creating a source file whose compilation we want to check:
> 
> #include <utype.h> // check for ICU headers
> 
> int main() { return 0; }
> 
> Then we create a target for it in our Jamfile, and mark it as explicit so it 
> doesn't get built by default:
> 
> obj my_test : my_cpp_file.cpp ;
> explicit my_test ;
> 
> Now we can use this in our main targets:
> 
> compile my_test_file.cpp :
> [ check-target-builds path_to_jamfile//my_test
>     :
>     # options if test succeeds:
>     <define>TEST_ICU=1
>     :
>     # options if test fails:
>     <build>no ] ;
> 
> Of course it would be easier if this was all wrapped in in some kind of 
> autoconf emulation layer....

Of course, I can add some higher-level wrapper. However, an important question
is whether we want to try linking against the found library, or not.
autoconf, I believe, generally tries to link. CMake, on the other hand,
basically searches for a file in some locations and that it -- it does not
try linking. Which behaviour seems more useful?

Thanks,

--
Vladimir Prus
http://vladimir_prus.blogspot.com
Boost.Build: http://boost.org/boost-build2