Re: [Boost-build] Generated header files.

Subject: Re: [Boost-build] Generated header files.
From: Mathias Lorente (mathias.lorente_at_[hidden])
Date: 2008-12-04 03:34:42

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.
- 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
      ;

And for the header generator: exe gen : gen.cpp ;

Many thanks for your help.
Mathias
> This assumes that your tool accepts source file as parameter and prints output to stdout.
> Note that $(<) is the name of the output file, including directory -- if your tool
> always outputs files in the current directory you might want to use this:
>
>  	actions generate-header 
> 	{
> 		cd $(<:D)
>  		$(>[1]) $(>[2]) > $(<:D=)
>  	}
>
>
>   
>> Then I could probably generate a list of input files and use  
>> your piece of script (or try to use the generator from standard module).
>>     
>
> Using generator, of course, it also possible. But in that case it's best to
> have your input files have a specific extensions, so that they can be automatically
> processed.
>
> - Volodya