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[Kurt Hornik]

>>>>> Thomas Lumley writes:

> On Mon, 2 Oct 2000, Peter Holzer wrote:
>> Dear R users
>> 
>> I have started to use gdb for debugging dynloaded C code as described in
>> `Writing R Extensions'. Unfortunately I have run into several problems that
>> I haven't been able to solve:
>> 
>> - using `n': how comes that the same line of code appears up to three times
>> (and inbetween the next line and maybe even the second next one?)
>> 
>> - using `print' resp. `display': How comes the variable values are
>> different from those shown by fprintf? How comes the variable values
>> change when actually no value is assigned to them (and I use `n', not
>> `s')?

> I think both problems are likely due to compiler optimisation.  The
> GNU tools are unusual in letting you debug optimised code: the Sun
> compilers, for example, won't generate debugging information if you
> optimise, for precisely this reason.

> Optimisation typically results in the machine instructions for
> different lines of C code being interleaved.  Even worse, loops may be
> unrolled, statements moved in or out of loops, and other complicated
> things done to your code.

> While debugging optimised code can still be useful, it is often easier
> to recompile the code without optimisation (as long as the bug isn't
> caused by optimisation) and debug that way.

> I'm not sure of the best way to recompile without optimisation. You
> could edit R_HOME/etc/Makeconf, or you could cut-and-paste the
> compiler invocations that R COMPILE produces and then edit them by
> hand.

Or, if you don't want to edit this file, you can do

	MAKEFLAGS="CFLAGS=" R CMD INSTALL /path/to/code

etc.

(Not sure if all versions of make support this ... if so maybe this
should be an FAQ?)

-k
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