On Wed, 2 Dec 2009, Arne Vajh?j wrote:
Martin Gregorie wrote:
I have never got on with debuggers, so I tend to load up my programs
with trace statements that output to stderr. So far, so conventional,
however I also add command line options to control debugging detail
by setting a 'debug' integer and always leave this stuff in
production code because the speed impact of testing integer values
and skipping debug statements is minimal and the diagnostic value of
this trick during live running is huge.
I completely agree that debuggers are great for debugging toy
programs, but log output is often much better for real world programs.
I think they're for completely different purposes. Logging is for
figuring out roughly where an problem is - your application is behaving
badly, so you have a look at the logs , and you see warnings suggesting
something's wrong in the furnace or whatever. A debugger is for figuring
out why a component is causing a problem - you attach to the furnace and
fire various inputs at it and follow execution, and see where invariants
are violated, where the wrong branch is being taken, where nulls are
creeping in, etc.
I find i get a lot more use out of the debugger early on in development,
when i'm actually writing something and its internal behaviour is still
in flux. Later on, when things are more about integration and
discovering corner cases, it's often "hmm, i see the turntable is
crashing when i load colours with a lot of blue in them - oh yeah, i
only allowed forty bytes for blue, that's what it is", and you don't
even need to look hard at the code or debug to figure out the solution.