Re: Preconditions vs. Dependencies

[John Graham-Cumming]

natch wrote:
> I'm having a dependency problem that I can't find a good solution to.  I 
> want to create files inside a directory other than that in which make is 
> executing.  The easy solution is that the files depend on the directory 
> they are in, so make will not try to create the files unless the 
> directory is created first.  However, if more than one file is created 
> in that directory, the timestamp on the directory is updated, and make 
> considers that prerequisite newer than the target.  Consider the 
> following makefile:
>
> DIR=outdir
> FILES=$(DIR)/a $(DIR)/b $(DIR)/c
>
> $(DIR):
>    mkdir $@
>
> $(FILES): $(DIR)
>    touch $@

A simple way to make this work is to have a file in each directory that 
is used to indicate the existence of the directory and can be safely 
used as a prerequisite in Make avoiding the remaking problems that you 
are seeing.

For example, every directory you create could have a file called '.f' in 
it made with a rule like this:

    $(DIR)/.f:
        mkdir (@D)
        touch $@

and then you could have the $(FILES) depend on that file:

    $(FILES): $(DIR)/.f

If you are creating different directories then you can use a pattern rule:

    %/.f:
        mkdir $*
        touch $@

John.
--
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