Re: "generating prerequisites automatically" causes all *.d makefiles to be regenerated?

[Peter Johnson]

Mark,

Unfortunately the GNU Make manual does not recommend the "right thing".

The trick is that you should build the dependencies when you run the  
compile. They are only needed for the next compile anyway, not the  
current. Make knew it needed to build foobar.o since it didn't exist.  
It is only on the next run that it needs the dependency generation.

See http://make.paulandlesley.org/autodep.html for details on how to  
really do the "right thing".

-Pete

On Oct 19, 2009, at 1:43 AM, Mark Galeck (CW) wrote:

> Hello,
>
> I read and implemented the guidelines in the section of the GNU Make  
> manual “4.14 Generating Prerequisities Automatically”.  It works  
> great, for each C source file, I have a corresponding .d file, which  
> is also a makefile, generated, and all those makefiles are included  
> in the main makefile with the “include” directive.  In the .d file  
> are header file dependencies for that particular C file.
>
> There seems to be a problem however with this approach.  I write  
> “seems” because it must be that I don’t understand something, as I  
> am sure the GNU Make manual recommends the “right thing”.  Please  
> help me understand what I am missing.
>
>
>
> The problem I have is:  when I do
> >make foobar.o
>
> make then tries to generate all these *.d files, all of them – not  
> just the one that is needed foobar.d !  That is not good –takes a  
> lot of time if I just want one foobar.o.  Also, what is worse,
> if I do
>
> >make clean
>
> Then again, all the *.d files are generated first, takes a very long  
> time, before everything is deleted.
>
>
> How to do it so that only the *.d files that are really needed are  
> generated, and none are generated on make clean?
>
> Thank you for any insight,
>
> Mark
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