Re: question about Generating Prerequisites Automatically

[Lin George]

Thanks Paul!


> You're right, it does not make much sense to have
> intermediate files
> without any prerequisites.  The only time the
> intermediate file will be
> rebuilt then is if the upper target doesn't exist;
> in that case all the
> intermediate files are considered out of date and
> rebuilt.
> 
> However, that's not how intermediate files are
> generally used; they are
> used to avoid rebuilding files "in between" the
> ultimate target and the
> source files.

I think the complete rule when intermediate file will
be remade should be,

1. dependent file is newer than ultimate target file;
2. upper file does not exist.

Is that correct?

About the incremental build, I do not think it will
utilize intermediate files to achieve the function of
incremental build, since I am using ar to generate
static libraries, but I am not using intermediate
files. :-)

It seems that you mean if I use intermediate file
together with ar, it will be more efficient or
something?


regards,
George

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

> %% Lin George <address@hidden> writes:
> 
>   >> An ordinary target is updated if EITHER its
> prerequisites are
>   >> newer, OR the target doesn't exist.
>   >> 
>   >> An intermediate target is updated ONLY if its
> prerequisites are
>   >> newer.
> 
>   lg> This is exactly what I am looking for. I
> remembered
>   lg> that you have mentioned before intermediate
> file is
>   lg> useful for increasement build or something. Is
> that
>   lg> correct?
> 
> Incremental builds; yes.  Consider static libraries,
> or archives
> (libfoo.a).  The ar program, that builds these
> libraries, can add,
> remove, and replace individual .o's inside an
> already-existing archive.
> 
> That means that if you have a libfoo.a that contains
> foo.o, bar.o, and
> baz.o you can replace just baz.o in the archive even
> if foo.o and bar.o
> don't exist.  This makes it different from (most)
> linkers, which require
> ALL the objects to exist when the link is performed.
> 
> There do exist "incremental linkers" but they are
> rare these days: the
> performance improvements have generally been
> determined to not be worth
> the added complexity in most cases.
> 
>   lg> I think if it is true, increasement build will
> suffer from the
>   lg> issues of intermediate files -- they will not
> be remade even if
>   lg> they are "needed", for example, the
> intermediate files without any
>   lg> dependencies will suffer from this issue. I am
> not sure why
>   lg> increasement build will choose intermediate
> file.
> 
> You're right, it does not make much sense to have
> intermediate files
> without any prerequisites.  The only time the
> intermediate file will be
> rebuilt then is if the upper target doesn't exist;
> in that case all the
> intermediate files are considered out of date and
> rebuilt.
> 
> However, that's not how intermediate files are
> generally used; they are
> used to avoid rebuilding files "in between" the
> ultimate target and the
> source files.
> 
> -- 
>
-------------------------------------------------------------------------------
>  Paul D. Smith <address@hidden>          Find some
> GNU make tips at:
>  http://www.gnu.org                     
> http://make.paulandlesley.org
>  "Please remain calm...I may be mad, but I am a
> professional." --Mad Scientist
> 


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