Re: Inconsistent use of vpath

[normvcr]

Philip Guenther-2 wrote:
> 
> On Sat, Jun 2, 2012 at 2:17 PM, normvcr <address@hidden> wrote:
>> I have come across a puzzling problem while building with make.
>>
>> make all
>>
>> While building the targets, make eventually comes to building
>> foo.o, but quits with an error, that it cannot find foo.cpp .
>>
>> However, when I now do, again, at the OS prompt:
>>
>> make all
>>
>> make picks up where it left off, and  succeeds; the echo of the command
>> shows that make
>> is correctly using  .../src/foo.cpp  through the vpath directives.
>>
>> My question is, why did make not find .../src/foo.cpp  in the course
>> of the original invokation of make?
> 
> I believe the most common cause of this is because some makefile rule
> builds a file other than address@hidden  In this case, ../src/foo.cpp  didn't
> exist before the first run but did afterwards, but make didn't know
> that some rule that it had run had created it.  What was the rule that
> generated ../src/foo.cpp?
> 

There is, indeed, a target that first creates foo.cpp, but it only
overwrites an an old, existing, foo.cpp .  It is as though the creation of
the new foo.cpp is changing the rules, as you suggested, above, even
though there was already a foo.cpp before invoking make the first time.

Any ideas how to work around, that?  Perhaps, if I break up the 
rule into two rules (first make foo.cpp, then make foo.o), 
that should simplify things for make, but should such a work-around
be necessary?


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