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Re: question about Generating Prerequisites Automatically

From: Lin George
Subject: Re: question about Generating Prerequisites Automatically
Date: Mon, 8 May 2006 00:09:26 -0700 (PDT)

Thanks Paul,

Why in the sample you made, when bar.o is deleted,
then it will not be remade when we make prog again? I
think the target prog needs bar.o and bar.o does not
exist -- so it should be remade. Any rules mentioned
in GNU make manual prevents it from being remade?


--- "Paul D. Smith" <address@hidden> wrote:

> %% Lin George <address@hidden> writes:
>   lg> Another comment is that, I think the way how
> make deals with
>   lg> intermediate files is smarter than the way
> dealing with ordinary
>   lg> files -- by saving time of remaking
> unnecessary files. So, why
>   lg> make does not change the way dealing with
> ordinary file to the
>   lg> (smarter) way dealing with the intermediate
> file?
> Very simple: it often is not at all what you want.
> Consider what happens:
>     prog: foo.o bar.o
>     .INTERMEDIATE: foo.o bar.o
> Now, we run make:
>     cc -o foo.o -c foo.c
>     cc -o bar.o -c bar.c
>     cc -o prog foo.o bar.o
> Since there's no "prog" everything is out of date. 
> So far so good.
> Now, we delete bar.o... uh oh!
>     cc -o prog foo.o bar.o
>     cc: no such file or directory: bar.o
> Intermediate files ONLY work with targets that can
> be _incrementally
> built_, or which are built from only one source. 
> Things like libraries,
> where the "ar" program can add new objects to an
> archive without
> recreating it from scratch, are good examples of
> this.  Or, copying
> files from a staging area into a production area,
> where each file is
> managed individually.
> If the target needs all the prerequisites to exist
> at once, like a
> linker, then intermediate files don't work.
> -- 
>  Paul D. Smith <address@hidden>          Find some
> GNU make tips at:
>  "Please remain calm...I may be mad, but I am a
> professional." --Mad Scientist

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