Learning C

[Nick Keighley]

"Chris"posted the following on 2006-03-10:

"debugger" / "debuggers" whatever. I've used ddd.


I stress that I talking about "stepping through an application". I have
*no*
objection to examining existing code. One way to learn is to look at
good
examples (and sometimes at bad).

No they dont : you have to insert them in the code.

yes, but you don't have to keep on inserting them. Debuggers are
generally manual.

But thats being petty.

I beg to differ.

Its rare that I find someone wanting their printfs to be
portable in a system process or a an X gui or a Win 32 winproc : they
dont work. Home grown or system supplied logging libraries possibly :
but can you really analyse them at run time? I cant : I like to step
through and see the flow of the app to get a feel for how the systems
heart is beating.

ok I'm not saying you are wrong. I'm just pointing out that not
everyone
works and learns the way you do. I don't single step debuggers to
examine other people's applications


using a debugger to examine existing applications


*examining* existing applications and other examples, yes.
*stepping* existing applications and other examples, no.


right. BUT NOT IN A DEBUGGER

Really? Seems pretty straightforward to me and also how close on 100% of
Universities teach coding at some stage or other :

really? *all* universities encourage the use of stepping?
Do you have statistics?

Could you go back and *read* what I and other posters have actually
been saying?

adding modules to existing systems.

yes! absoloutly!

Maybe I'm a bit slow today but I'm not seeing the
subtleties of the point you are making here :

well you don't "add to an existing module" by using a debugger.

the user is looking for
a way to learn how to structure applications and build them himself.

yes yes

I fail to see how analysing existing, successful apps can be anything
other than beneficial. It doesnt take away the donkey work of learning
the lanugage basics, but it can make text book "science" much more
accessible and "real". I cant imagine becoming a programmer without
such practice, guidance and "practical training". Its the same in all
walks of life.

I think I'll give up here. My point wasn't that important. Just trying
to
make the point that different people do thinks in different ways. Linux

is not the only platform. Not everyone uses debuggers the way you do
(some people only use them when they suspect a compiler error). A
newbie should be aware there are different ways to do things and not
lock themselves into a particular approach too early.

Maybe I'll even get my debugger out and step through a program
sometime to see if it brings me any insights. Maybe you should try
a "debugger free day" and try and see what you have to do to manage
without. Try reasoning about the program. Consider invariants and
post/pre conditions. Try adding asserts etc.

no way is the One True Way

"A desk is a dangerous place from which to view the world" - LeCarre.

"there is nothing as practical as a good theory" Lewin

 

[Richard G. Riley]

"Nick"posted the following on 2006-03-11:

"debugger" / "debuggers" whatever. I've used ddd.

ddd is a front end to gdb.

I stress that I talking about "stepping through an application". I have
*no*
objection to examining existing code. One way to learn is to look at
good
examples (and sometimes at bad).

And how can stepping through an app be bad? Were you never put onto a
new project with a code base of several hundred thousand lines of code
and told to isolate some relatively bugs to get you familiar with the
code base?

yes, but you don't have to keep on inserting them. Debuggers are
generally manual.



I beg to differ.

I meant me pointing out they are useless in most server based apps or
message driven GUI apps.

ok I'm not saying you are wrong. I'm just pointing out that not
everyone
works and learns the way you do. I don't single step debuggers to
examine other people's applications

Thats fine Nick : I dont expect you too - but you seem to have strong
reasons for making a point against it whereas I see *only* benefits.

using a debugger to examine existing applications

We wont get into the pissing contest of who has worked on more
apps/platforms etc but I find it a good teaching tool to get people up
to speed with an app and its internal data structures : modify on the
fly, symbol tables etc. Cant do that with a print out or printfs.

*examining* existing applications and other examples, yes.
*stepping* existing applications and other examples, no.

for me "examining" is "stepping" : but obviously with some
strategically placed break points and a few retunr to callers etc

right. BUT NOT IN A DEBUGGER

Really : in a debugger. Do you really advocate printfs over a debugger
in a huge code base? How do you map data values to their equivalent
constants? To me it sounds incredible. If you hadnt mentioned ddd I
would wonder if we are talking about the same thing.

really? *all* universities encourage the use of stepping?
Do you have statistics?

Maybe stepping is the key word here : it does not mean every line. It
means strategically placed break points and data analysis at those
points. It is an art.

Could you go back and *read* what I and other posters have actually
been saying?

I did. Some people seem to think that a debugger is just for finding
bugs : it is not. It is also useful for examining runtime trends. Far
more useful than hard to decipher printfs, especially in a non console mode.

yes! absoloutly!



well you don't "add to an existing module" by using a debugger.

Of course you do. You use it to examine the data flow between the
system and your module.

yes yes



I think I'll give up here. My point wasn't that important. Just trying
to
make the point that different people do thinks in different ways. Linux

is not the only platform. Not everyone uses debuggers the way you do

Nobody said it was : you came flying in with that. The OP had
expressed an intrest in Linux and the fact that it comes with free
industry strength compilers and debuggers as well as hundreds of rock
solid C apps complete with build packages makes it a good bet for
someone to learn how to structure and analyse an application in
C. Windows can not compete with that IMO.

(some people only use them when they suspect a compiler error). A

If there is a compile error, you wont be using a debugger.

newbie should be aware there are different ways to do things and not
lock themselves into a particular approach too early.

A newbie needs to examine other peoples stuff : especially when
adding/fixing bugs. Approaches vary, but it can never hurt to get down
and dirty to be sure.

A newbie certainly shouldnt dedicate his life to printf()'s : they
simply do not work in a lot of environments, are inflexible, and only
show the data that you WANT to see, not the data you SHOULD see. This
is where a debuggers "locals" view etc comes in. You see alllocal
data. Not what someone thinks they need to see.

Maybe I'll even get my debugger out and step through a program
sometime to see if it brings me any insights. Maybe you should try
a "debugger free day" and try and see what you have to do to manage
without. Try reasoning about the program. Consider invariants and
post/pre conditions. Try adding asserts etc.

If you recall I did mention that a home brew logging system is
prefential to printf : I have nothing against them and have
implemented many with various backend report generators to examine the
data. A debugger isnt the only tool : and I never said it was. What it
can do is allow you to see the flow of an application while watching
live data, allow you to modify that data and to examine and ensure
data typing is consistant from skillful use of register/pointer/memory
examinations : it is why they exist.

no way is the One True Way

And no where did I say it was. The whole crux here is you doubting
that stepping an existing app can help a user understand it : after
many, many and varied projects on various platforms in various
languages I find it incredulous how you could doubt this would be
beneficial. In order to even put in these printfs() you need some
understanding of whats going : that does not come from a print out all
the time. It does not some from a func spec which is not always
there. It does not come from holistic overview : it comes from
stepping through and examining what is going on. From finding out when
and why certain modules are called. From knowing what that little bit
of bit fiddling results in, from forcing a function call at runtime in
order to test a different calling parameter. The list goes on. Of
course none of this is "the only way" : but its a good way and one
thats been used a lot for years.

Do you need a debugger for a ten line string rversal func? Maybe not :
but I'll tell you a little secret, I'd still use one to test it
rigorously before handing it in to a system for an integration
test. Total extra effort? About 5 minutes.


I realise that there is a core here who seem to think a debugger is
almost evil : I sometimes question if they have used a real
debugger on a real system in the real world where programmers are
cycled on and off projects and people want to optimise their "up to
speed" figures. I realise that according to some posters some projects
get by without a debugger : I've never had the pleasure of such a
project/system.

 

[Nick Keighley]

"Nick"posted the following on 2006-03-11:

ddd is a front end to gdb.

I know

And how can stepping through an app be bad? Were you never put onto a
new project with a code base of several hundred thousand lines of code
and told to isolate some relatively bugs to get you familiar with the
code base?

about a year ago I was put on 750 kloc application. I had no previous
experience with the application. And limited experience with the
programming language. I did not step through the code with a debugger.

I meant me pointing out they are useless in most server based apps or
message driven GUI apps.

there are alternatives to printf(). I usually use some sort of logger.
For both
servers and GUIs. That 750kloc application has both.

Thats fine Nick : I dont expect you too - but you seem to have strong
reasons for making a point against it whereas I see *only* benefits.

ok, we disagree. What's wrong with *reading* the code. UML? Source
browsers?

We wont get into the pissing contest of who has worked on more
apps/platforms etc but I find it a good teaching tool to get people up
to speed with an app and its internal data structures : modify on the
fly, symbol tables etc. Cant do that with a print out or printfs.

I have *never* had any desire to do these things. Find the bug. Fix
the bug. Why would you want to modify things on-the-fly?!

for me "examining" is "stepping" : but obviously with some
strategically placed break points and a few retunr to callers etc

"examine", to me, means to study the source code. A good source
browser can be handy.

Really : in a debugger. Do you really advocate printfs over a debugger
in a huge code base?



How do you map data values to their equivalent
constants? To me it sounds incredible. If you hadnt mentioned ddd I
would wonder if we are talking about the same thing.

some constants get dumped as numbers. Some enums are already wrappered
so as to be able to decode themselves (ok I admit this is C++, ...its
only a
*little bit* of a move to the Dark Side. I can stop any time I want).

Maybe stepping is the key word here : it does not mean every line. It
means strategically placed break points and data analysis at those
points. It is an art.

and *all* universities teach it? Its a long time since I was at
university.

Yorkshire Man 2:
"Symbolic debuggers! You were lucky we 'ad t'punch t' cards with ar
teeth!"

I did. Some people seem to think that a debugger is just for finding
bugs : it is not. It is also useful for examining runtime trends. Far
more useful than hard to decipher printfs, especially in a non console mode.

but you have to know where to put the breaks. And that means you must
at
least partially understand the application. To do that I'd read the
code...

Of course you do. You use it to examine the data flow between the
system and your module.

well I add to an existing module with a Text Editor. I'm not being
funny
here we *really* seem to be missing each others point.

I REALLY don't use a debugger to add code to an existing module.

Nobody said it was : you came flying in with that.
riight

The OP had
expressed an intrest in Linux and the fact that it comes with free
industry strength compilers and debuggers as well as hundreds of rock
solid C apps complete with build packages makes it a good bet for
someone to learn how to structure and analyse an application in
C. Windows can not compete with that IMO.

it's a perfectly good development platform though. Look Linux is ok.
Windows is ok. But two posters had encouraged the OP to move to
Linux. I'm not sure its such an open and shut decsision. You can
write crap non-portable code on Linux as well.

If there is a compile error, you wont be using a debugger.

well compiler bugs are about as rare as hens teeth. But why not? The
debugger would show you that the program flow or calculation results
did not follow the source code. All my tools are broken if the source
code does not represent what the machine is doing.

To be honest I can't remember the last time I had a bug caused by a
compiler error

A newbie needs to examine other peoples stuff : especially when
adding/fixing bugs. Approaches vary, but it can never hurt to get down
and dirty to be sure.

A newbie certainly shouldnt dedicate his life to printf()'s : they
simply do not work in a lot of environments, are inflexible, and only
show the data that you WANT to see, not the data you SHOULD see. This
is where a debuggers "locals" view etc comes in. You see alllocal
data. Not what someone thinks they need to see.


If you recall I did mention that a home brew logging system is
prefential to printf :

where did the words "homebrew logging system" appear in the paragraph
above? I did write a fairly blunt paragraph here. And then thought
better of it.
Do you know what an invarient is? Design by contract?

I have nothing against them and have
implemented many with various backend report generators to examine the
data.
good!

A debugger isnt the only tool : and I never said it was. What it
can do is allow you to see the flow of an application while watching
live data, allow you to modify that data

never felt the need. Not since compilers got fast enough to run during
the day.

and to examine and ensure
data typing is consistant from skillful use of register/pointer/memory
examinations : it is why they exist.

you examine registers? On a deeply embedded system, ok. But a server?

And no where did I say it was. The whole crux here is you doubting
that stepping an existing app can help a user understand it : after
many, many and varied projects on various platforms in various
languages I find it incredulous how you could doubt this would be
beneficial. In order to even put in these printfs() you need some
understanding of whats going : that does not come from a print out all
the time. It does not some from a func spec which is not always
there. It does not come from holistic overview : it comes from
stepping through and examining what is going on. From finding out when
and why certain modules are called. From knowing what that little bit
of bit fiddling results in, from forcing a function call at runtime in
order to test a different calling parameter. The list goes on. Of
course none of this is "the only way" : but its a good way and one
thats been used a lot for years.

I'd say the same went (in spades) for stepping. You've got to know
where
to step. There's source code, case tools, source browsers, source code.
I've even resorted to grep to find callers of functions.

Do you need a debugger for a ten line string rversal func? Maybe not :
but I'll tell you a little secret, I'd still use one to test it
rigorously before handing it in to a system for an integration
test. Total extra effort? About 5 minutes.

I'd write unit test. Also five minutes work and more likely to give
proper
coverage.

I realise that there is a core here who seem to think a debugger is
almost evil : I sometimes question if they have used a real
debugger on a real system in the real world where programmers are
cycled on and off projects and people want to optimise their "up to
speed" figures.

normally I don't get into what I work on, but yes I do work on projects

where people get cycled on and off. I'm one of the cycled. It's a real
system. In the real world. Real people pay real money for the
facilities
it provides. And there is a requirement for more performance.

I'm not accusing you of it, but sometimes people seem to spend way
too much time hunched over a debugger when a bit of thought might
save them some time.

 

[Richard G. Riley]

I know



about a year ago I was put on 750 kloc application. I had no previous
experience with the application. And limited experience with the
programming language. I did not step through the code with a

debugger.

Your choice. I would have. Especially when I modified the code. But
again you are offering no evidence to suggest that stepping through an
app is "crazy" or "bizarre" as you originally claimed.

there are alternatives to printf(). I usually use some sort of logger.
For both
servers and GUIs. That 750kloc application has both.

Fine. But often loggers affect the app. And again, you only see what
you are told you can see.. : a debugger lets you see what you want to
see when you want to see it. Being able to see the data greatly
simplifies understanding an application and I cant expect anyone to
dispute that. But someone will ... :-;

ok, we disagree. What's wrong with *reading* the code. UML? Source
browsers?

Because not all code is readable? Because not all code can be properly
deciphered from reading? Because you dont know what data is coming up
from those functions 40 deep? Becuase its plagues with missplaced
casts?

You dont know what branch conditions are going to be taken based on HW
port values? There are numerous reasons.

I have *never* had any desire to do these things. Find the bug. Fix
the bug. Why would you want to modify things on-the-fly?!

Modify data to test or force a state. Its a basic of debugger use : you can
force your hand to avoid having to wait for a certain random data
suite to trigger the bug.

e.g someone says I'm getting a divide by zero somewhere near func().

go to func in debugger, force a zero into the divisor and see why the
checks arent stopping it. Simple example.

"examine", to me, means to study the source code. A good source
browser can be handy.

A good debugger is that too.

some constants get dumped as numbers. Some enums are already wrappered
so as to be able to decode themselves (ok I admit this is C++, ...its
only a
*little bit* of a move to the Dark Side. I can stop any time I want).

I'm not good at remembering what 0xefecda means. I prefer something in
the debugger like "WM_GETFOCUS" or some such.

and *all* universities teach it? Its a long time since I was at
university.

me too.

Yorkshire Man 2:
"Symbolic debuggers! You were lucky we 'ad t'punch t' cards with ar
teeth!"




but you have to know where to put the breaks. And that means you must
at
least partially understand the application. To do that I'd read the
code...

So do I: of course. But i also analyse the flow at the same time : a
debugger does let you read the code you know :-;

well I add to an existing module with a Text Editor. I'm not being
funny
here we *really* seem to be missing each others point.

No you dont. You use a text editor to create the symbolic equivalent
which is then compiled & linked into the bigger app. The debugger can then be
used to force data between your interfaces and the legacy very easily
for the purposes of quick integration testing. Yes, there are other
ways too.

I REALLY don't use a debugger to add code to an existing module.

No. Nor do I. I use it, frequently, to monitor the addition. No one
here is suggesting the debugger is a compiler & linker & editor. It is
for me part of the process. Not for all, but we're heading back down
that well covered track again

riight

You did. Look at the thread. The OP mentioned Linux : I said it was a
good idea for what he wanted to do : you came in with "hold on hold on
lets not start an OS war here".

it's a perfectly good development platform though. Look Linux is ok.
Windows is ok. But two posters had encouraged the OP to move to
Linux. I'm not sure its such an open and shut decsision. You can
write crap non-portable code on Linux as well.

But you dont have the facilities to support his learning as well IMO :
remember me mentioning the thousands of apps with source code? No one
is saying Linux is "better", but I would say its better for someone
wanting to get into C programming big time : everything is part of the
base install. For Free. And documented.

well compiler bugs are about as rare as hens teeth. But why not? The
debugger would show you that the program flow or calculation results
did not follow the source code. All my tools are broken if the source
code does not represent what the machine is doing.

To be honest I can't remember the last time I had a bug caused by a
compiler error

Different things. I meant compilation error : sorry.

where did the words "homebrew logging system" appear in the paragraph
above? I did write a fairly blunt paragraph here. And then thought
better of it.
Do you know what an invarient is? Design by contract?

I used those words. Its when you wrap whatever underlying logging system is
convenient to you in a fairly generic calling interface : so you could
log to files, text consoles, window systems whatever without changing
the calling code.

never felt the need. Not since compilers got fast enough to run during
the day.

I really dont understand this. What has that got to do with a debugger?

you examine registers? On a deeply embedded system, ok. But a

I also mentioned memory and pointers. And yes I do. Very useful in
debugging big C systems.

I'd say the same went (in spades) for stepping. You've got to know
where
to step. There's source code, case tools, source browsers, source code.
I've even resorted to grep to find callers of functions.

grep is ok : if I dont have a decent IDE I use something like emacs
tags. I have used grep in about 15 years

I'd write unit test. Also five minutes work and more likely to give
proper
coverage.


normally I don't get into what I work on, but yes I do work on projects

where people get cycled on and off. I'm one of the cycled. It's a real
system. In the real world. Real people pay real money for the
facilities
it provides. And there is a requirement for more performance.

I'm not accusing you of it, but sometimes people seem to spend way
too much time hunched over a debugger when a bit of thought might
save them some time.

No doubt. And equally the opposite applies : in my experience more so.

 

[Keith Thompson]

I know


about a year ago I was put on 750 kloc application. I had no previous
experience with the application. And limited experience with the
programming language. I did not step through the code with a debugger.

[...]

If I might summarize:

Richard G. Riley really likes debuggers. Not everyone else likes them
as much as Richard does.

I believe that covers all the relevant points.

Next?

 

[Richard G. Riley]

If I might summarize:

Richard G. Riley really likes debuggers. Not everyone else likes them
as much as Richard does.

I believe that covers all the relevant points.

Next?

Very droll.

But not at all what the crux of this is about : what its about is a
one way of working which can dramatically speed up ones familiarity
with a system. I find it terrifying that there seems to be a fair
number of programmers here who think a debugger is "only for finding bugs"
: it is a limited and naive view.

Inserting printfs, asserts and so forth is time consuming, messes up
the code, limits one to what the programmer wanted you to see at
"write time", and is a colossal source of heisenbugs. Unless you're
perfect that is : which some here have indeed claimed to be.

And for using such a tool to be called "bizarre" is bizarre in
itself. Yes, yes, I know what Kernighan said : good on him.

The entire thread started with discussing how a new programmer could
familiarise himself with bulding & architecting apps : I'm afraid that
"look at the source code" simply isnt a credible answer. One learns by
doing and examining a running system compiled with debug is one of the
most productive tools in the trainers arsenal.

Next?

 

[Mark McIntyre]

with a system. I find it terrifying that there seems to be a fair
number of programmers here who think a debugger is "only for finding bugs"
: it is a limited and naive view.

is this thread still going, or has my newsprovider regurgitated it?
Either way, i find it terrifying that someone thinks a debugger is for
programme analysis and testing. Yike.
Mark McIntyre

 

[CBFalconer]

.... snip ...

If I might summarize:

Richard G. Riley really likes debuggers. Not everyone else likes
them as much as Richard does.

I believe that covers all the relevant points.

Which buggers?

--
"If you want to post a followup via groups.google.com, don't use
the broken "Reply" link at the bottom of the article. Click on
"show options" at the top of the article, then click on the
"Reply" at the bottom of the article headers." - Keith Thompson
More details at: <http://cfaj.freeshell.org/google/>
Also see <http://www.safalra.com/special/googlegroupsreply/>

 

[Ian Collins]

Very droll.

But not at all what the crux of this is about : what its about is a
one way of working which can dramatically speed up ones familiarity
with a system. I find it terrifying that there seems to be a fair
number of programmers here who think a debugger is "only for finding bugs"
: it is a limited and naive view.

There is the middle ground, read the code first and step tough bits you
can't sus out in the debugger. A decent source browser (one that gives
you callers and callees) is a better tool for the job, it gives you an
overview of the code, rather than the details of one part of it.

Using a debugger as the main tool for familiarising one's self with a
large body of code is a bit like using a microscope to read a book.

 

[Nick Keighley]

[ a long debate partly about using a debugger to analyse existing,
working
applications. Richard G. Riley thinks it's a good idea. I (Nick
Keighley) don't]

ok. This is *way* off topic. It has gone on too long. And the post has
grown
to gigantic proportions. I'm *really* going to stop now (I think I said
that
before...).

We are both probably frustratrated that the other doesn't seem to
understand our perefectly reasonable point of view. And everyone else
on
clc is probably even more frustrated that we both keep banging on.

What I do find odd is that we have drawn opposite conclusions for the
same
reason. Neither of us likes doing things manually that can be automated

(sign of a good programmer). So Richard objects to using printf() (or
custom
logger) because it is manual, error prone and may disturb the program,
and prefers using a debugger to achieve the same end. I object to the
use
of a debugger ***for exactly the same reasons*** !

I find [a debugger] a good teaching tool to get people up
to speed with an app and its internal data structures : modify on the
fly, symbol tables etc. Cant do that with a print out or printfs.

I have *never* had any desire to do these things. Find the bug. Fix
the bug. Why would you want to modify things on-the-fly?!

Modify data to test or force a state. Its a basic of debugger use : you can
force your hand to avoid having to wait for a certain random data
suite to trigger the bug.

e.g someone says I'm getting a divide by zero somewhere near func().

go to func in debugger, force a zero into the divisor and see why the
checks arent stopping it. Simple example.

no. Put an assert() in. A modified variable is just for today. An
approriate
assert() lasts forever. Next year when someone casts doubt on the same
function, you simply look at the func() source code and say "nope,
can't
be a divide by zero because there's an assert() to check for that". Fix
it
once, never touch it again.

You did. Look at the thread. The OP mentioned Linux : I said it was a
good idea for what he wanted to do : you came in with "hold on hold on
lets not start an OS war here".

a debugger war is much more fun...

I used those words. Its when you wrap whatever underlying logging system is
convenient to you in a fairly generic calling interface : so you could
log to files, text consoles, window systems whatever without changing
the calling code.

I note you didn't say if you knew what "Design by Contract" meant.

I really dont understand this. What has that got to do with a debugger?

I've modified variables using the debugger (the "debugger" actually had

toggle switches...) when the run time of the compiler was significant.
If it
took hours to recompile your code then machine code patches and
register
hacking was acceptable. It is no longer necessary (well, sometimes).

I also mentioned memory and pointers. And yes I do. Very useful in
debugging big C systems.

wow. Culture Shockville. To my shame I couldn't even tell you what
registers
my platform has without STFWing. Ok that's a project for today.

grep is ok : if I dont have a decent IDE I use something like emacs
tags. I have used grep in about 15 years

ok it's a tool of desparation. You * never* use grep?!

<snip>

 

[Richard G. Riley]

There is the middle ground, read the code first and step tough bits you
can't sus out in the debugger. A decent source browser (one that

gives

100% of course. *Nothing* is as good as a good clear printout for an
overview and a familiarity. Hell, I print out man pages still.

you callers and callees) is a better tool for the job, it gives you an
overview of the code, rather than the details of one part of it.

Using a debugger as the main tool for familiarising one's self with a
large body of code is a bit like using a microscope to read a book.

I'm afraid that due to some of the replies I might have become a bit
exasperated and come across as a bit of a fanatic

But to close and to summarise some points which a lot of posters dont
seem to be aware of - or at least it appears that way from their
"debuggers are only occasional useful" replies -

1) A debugger can give you that high level overview too
2) It has cross reference facilities for definition finding
3) Ability to give symbolic representation to data
4) Ability to tweak at runtime to force unlikely conditions
5) Abilitiy to see entire dataset : not that determined useful by the
original programmer
6) Watchpoints & HW breakpoints to isolate required conditions.
7) Shows types : reveals bad casts & conversions very quickly in the
datawindow.


There are more. A good print out is good if for nothing else than
sitting on the jacks having a read Or annotation. The combo of a
good debugger with the experience of how to use it and possibly a
profiler is nirvana for a C programmer working on a large project.

I've seen old systems where the code is simply unreadable :
multistatements per line, single letter variable names, cast city :
code like this can be a nightmare to read from a printout - it is
useful to watch the program run. Yes, printfs* can be useful if
you have the knowledge and the facility to insert them.

(*) Or home brew multi-platform/interface compatible logging system
like Linux's klogd.

One last point about your microscope comment : this is only true if
you *step* every line. You dont. You place strategic break points at
the page or chapter you are interested in : after all, a C program is
hardly a novel - thought it is a schematic

And to anyone that got this far that isnt totally bored by the whole
thing : consider this. You see a function in a source browser :
are you not interested in HOW it was called? Why it was called? You can
guess from 30000 pages of printout or from a call hierachy in a source
analysys tool or IDE : but its 2 seconds work to set a break point
there and examine a few call stacks.

Yes, I'm an advocate. And astonished by the claims of some who say
they havent used a debugger more than twice in over 20 years of C programming.

 

[Richard G. Riley]

no. Put an assert() in. A modified variable is just for today. An
approriate
assert() lasts forever. Next year when someone casts doubt on the same
function, you simply look at the func() source code and say "nope,
can't
be a divide by zero because there's an assert() to check for that". Fix
it
once, never touch it again.

Thats not the example I gave. I gave the example to force the divide
by zero error : with no added code which changes the footprint between
runtime and debug models. To expand a bit, I might want to check a
deeply embedded function can handle an integer limit or a null
pointer. One very important issue
here is that I dont do this all the time - only when its deep in a
system where a quick glance cant quarentee the absence of such
"limits". I might want to call "convertBitmap()" with option 3 for GIF
since the test data framework didnt incude that option. Or 6 which is
not yet implemented.

Bottom line is that also, some systems dont want to exit : they want
to handle the assert condition more generously. assert is one up from
printf mind you. At least you can compile it out without running
around changing all your source. Not that I agree with code footprint
which is different between "real" and "development".

Also, how many times have we found

assert(a++);

as opposed to "assert(a);a++" in some remote rarely called routine?

Bad? Yes. But shit happens.

If what you want is required then yes, an assert is useful.

a debugger war is much more fun...

It can be.. (ps this is far from OT : it is about using C language mechanisms
for debugging aid which overrule the need for a HW/SW debugger). If it
was in the std group then yes.

I note you didn't say if you knew what "Design by Contract" meant.

It has nothing to do with what I am advocating here. And so I wont get
dragged into a terminology war. I'm not talking about designing
anything here. And if I wanted to bluff, google is a mere keypress away
:-;

Remember that the crux of this is that I'm saying it can be
advantageous for someone wanting to familiarise themself with a system
to see it runing under a good debugger. You claimed this as "bizarre".

I've modified variables using the debugger (the "debugger" actually had

toggle switches...) when the run time of the compiler was significant.
If it
took hours to recompile your code then machine code patches and
register
hacking was acceptable. It is no longer necessary (well, sometimes).

You must work on very small systems. I would never counter someone
modifying code here there and everywhere to *find* a bug when you can
get the same effect in less time without modifying the code.

What are toggle switches? What is a machine code patch in this
context? I would rarely advocate register hacking : the whole point of
a debugger is that it gives symbolic access to your system variables
and messing with registers is not required.

wow. Culture Shockville. To my shame I couldn't even tell you what
registers
my platform has without STFWing. Ok that's a project for today.



ok it's a tool of desparation. You * never* use grep?!

I used it today to find where a certain daemon was in a boot hierarchy
: nice.

OK, lets call it a day.