Re: The usefulness of application logging

apm35@student.open.ac.uk wrote:


It depends on what you mean by logging.

I think you probably mean output to some file showing the internal
state
of the program. I must say that it's pretty rare that I find this to be
useful
in production code.

There is an exception to that rule, though. Every once in a LONG while,
I'll come across a situation where my program is failing on a client
machine -- but works perfectly well on my own machine. The client
machine
doesn't have a debugger. For various reasons (not just licensing, but
that
would be enough!), I can't install a debugger on the client machine.

In those situations, it makes sense to create a special build of my
program, which can show me what's happening in the section that I think
is having problems. Basically, I can insert debugging probes in at
compile
time, instead of at runtime. I might add

    logfile << "Before func1: some_variable=" << some_variable << '\n';
    func1(whatever);
    logfile << "After func1: some_variable=" << some_variable << '\n';

When I've determined that the problem either is (or is not) being
triggered
by func1, I move the debugging lines and repeat the test... I continue
until
I understand where the problem is originating, at which time I can
remove
all of the debugging code and fix the problem, even though I never
reproduced it in a debugger.

This debugging technique is slow and painful, and requires active
cooperation from whoever uses the computer that is experiencing the
problem. Fortunately it's pretty rare that I need it anymore -- early
on
in my career I needed it every 6 months, but in the last 10 years I
doubt I've done this more than 3 times. But it's available when all
else fails.

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