Re: How does make compare the timestamp if the file does not exist

[Stephen Macmanus]

When make detects the target does not exist and runs the
associated rules, it also runs any rules which use the
new target as a prerequisite.

In this example, any execution of make will *always* run
the rule for "boo" (unless it is created outside make),
and therefore always run the rule for "foo" also.

Hope this helps,

Stephen Macmanus


雷 高 wrote:
> If the target of a rule does not exist or the timestamp of the target is 
> older than any of the prerequisites, the target is out of date. My 
> question is that if some files of prerequisites does not exist, how can 
> we compare the timestamp.
> For example:
> foo : boo
>         @echo foo
> boo :
>         @echo boo
> Then if foo already exists, but the rule for "boo" does not create the 
> file boo, so how compare the timestamp of foo and boo.
> When I run the makefile, the console prints :
> boo
> foo
> I want to know why the make parses the makefile like this.
>
> A more general problem is that how the make treat files which doesn't 
> exist and can't be created by explicit rules and implicit rules.
>
> Thank you for your answer!
>
>
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