About makefile

[Satish Balay]

The reason we delete the .o files and force a recompile each time for
examples is: not all dependencies are captured in our makefiles. For
eg: when switching PETSC_ARCH, or [as developers] - if PETSc sources
are changed for the same PETSC_ARCH. [examples don't have dependencies
that would force a recompile]

So its easier for us just to do recompile of examples each time - than
keeping track of the above changes [which happen constantly for us
developers]

As users the above issue might not matter [as most use a single
PETSC_ARCH, and the PETSC install hardly changes]. So - you can save
this time by not deleting .o files - and doing 'make clean' - when
you really need to reset.

Satish


On Fri, 9 Oct 2009, Brock Palen wrote:

> 
> 
> 
> On Oct 9, 2009, at 7:05 AM, jarunan at ascomp.ch wrote:
> 
> > Hello
> > 
> > After the compilation, is it compulsory to delete .o file?
> > Actually, once I found that .o file do not update unless I delete it before
> > recompiling. I might misunderstand. if not, I would like to know some reason
> > behind.
> 
> Make only recompiles files where the source file is newer than the resulting
> file (the .o file).  Thus if you have not modified the source file for a .o
> file, it will not be recompiled and will be relinked as is.  If you wish to
> force everything to recompile (maybe new compiler options etc)  then you need
> to delete all your old .o .a .so and .mod files.  So they are recreated with
> the new options.
> 
> This is a feature of make, that is really helpful, it keeps you from having to
> wait to recompile code that has already been compiled once, if it will not
> change.
> 
> Brock Palen
> www.umich.edu/~brockp
> Center for Advanced Computing
> brockp at umich.edu
> (734)936-1985
> 
> > 
> > 
> > Thank you
> > Jarunan
> > 
> > 
> > -- 
> > Jarunan Panyasantisuk
> > Development Engineer
> > ASCOMP GmbH, Technoparkstr. 1
> > CH-8005 Zurich, Switzerland
> > Phone : +41 44 445 4072
> > Fax   : +41 44 445 4075
> > E-mail: jarunan at ascomp.ch
> > www.ascomp.ch
> > 
> > 
> > 
>