Re: [Boost-build] Generated header files.

Subject: Re: [Boost-build] Generated header files.
From: Vladimir Prus (ghost_at_[hidden])
Date: 2008-12-04 04:04:39

On Thursday 04 December 2008 11:34:42 Mathias Lorente wrote:
> Vladimir Prus wrote:
> > On Wednesday 03 December 2008 19:09:16 Mathias Lorente wrote:
> >   
> >> Vladimir Prus wrote:
> >>     
> >>> On Wednesday 03 December 2008 17:36:05 Mathias Lorente wrote:
> >>>   
> >>>       
> >>>> Dear list,
> >>>>
> >>>> I use bjam to build a library which relies on some generated header files.
> >>>> These files are generated by a specific application which is also built 
> >>>> using bjam.
> >>>> I added a dependency for my library so that the application is built 
> >>>> before the library.
> >>>> But:
> >>>> - I didn't manage to launch the application in order to generate the 
> >>>> necessary header files before the library is being built.
> >>>>     
> >>>>         
> >>> Hi Mathias,
> >>>
> >>> it's generally best to show what approaches you've tried, so that you
> >>> get help about your specific issue, not some approximation. Generally,
> >>> something like this should work:
> >>>
> >>>
> >>> 	exe header_generator : header_generator.cpp ;
> >>> 	make header.h : header_generator : @generate-header ;
> >>> 	actions generate-header 
> >>> 	{
> >>> 		$(>) > $(<)
> >>> 	}
> >>> 	lib header_user : header_user.cpp : <implicit-dependency>header.h ;
> >>>
> >>> - Volodya
> >>>   
> >>>       
> >> Hello Volodya,
> >>
> >> Thanks for your reply.
> >> In fact my 'header generator' uses input files (let's say .txt) which 
> >> are parsed/modified/... to make the corresponding .h files.
> >> Until now, I was launching the generator by hand and it was working on 
> >> all files in the specified directory (as command line parameter).
> >> I suppose I would have to modify it in order to make it take one file at 
> >> a time. 
> >>     
> >
> > For dependency tracking, it's best if each invocation takes specific input
> > and produces a single file. Otherwise, Boost.Build or you would have to run
> > your tool on all files. Here's how to modify my code to make it accept a source:
> >
> >  	make header.h : header_generator input.txt : @generate-header ;
> >  	actions generate-header 
> > 	{
> >  		$(>[1]) $(>[2]) > $(<)
> >  	}
> >   
> I have modified my header generator which takes one input file and 
> writes the corresponding header file in the same directory as the input 
> file. So I have the following bjam script:
> 
>     make header.h
>       : ../utils//gen header.txt
>       : @generate-header
>       ;
> 
>     actions generate-header
>     {
>       $(>[1]) $(>[2])
>     }
> 
> But this solution does not meet some requirements:
> - Each time I launch bjam, the header generator is launched even if 
> header.txt has not been modified.

This means that your tool generates header not where Boost.Build wants
it to be -- which I've mentioned in the previous email.
Add 

        echo $(<)

to your actions. This will print the location where the header *should* be generated.
And then check if that location actually has the file. If you want the file to
be located somewhere else, use:

     make header.h
       : ../utils//gen header.txt
       : @generate-header
       : <location>somewhere
       ;

> - My library (which relies on generated header) is rebuilt only the 
> second time I launch bjam: first time, headers are generated, second 
> time, headers are generated and the library is rebuilt. I suspect that 
> bjam checks the timestamp of the header files before they are generated 
> again...
> Here is the definition to build my library:
> 
>     lib my_lib
>       : [ glob-tree *.cpp : .svn ]
>       : <link>static
>         <define>BUILDING_LIBRARY
>         <variant>debug:<define>ENABLE_DEBUG_LOG
>       ;

This lacks <implicit-dependency> -- which I've mentioned previously as well.
You can read about that in the docs:

        http://www.boost.org/boost-build2/doc/html/bbv2/reference/generated_headers.html

- Volodya