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Learning C with gdb

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Re: Learning C with gdb

#31

Post by sliverstorm »

jobu wrote: post #24
dkhenry wrote: post #10

GDB skills are one of those super useful abilities that you just can't find in most CS graduates. I often spend a few days with new C developers just teaching them how to use GDB to find problems. They are amazed when they find out you can examine variables and set conditional breakpoints.

This is an area where many college professors fall short. In my intro to CS class we learned C, and the professor explicitly told us to debug our code with printf statements. It wasn't until my first job that I even found out about gdb. I can't believe how much time I wasted trying to debug C and C++ code in college with nothing more than printf and cout.

gdb being a utility, I believe the student is generally expected to learn it on their own if they like. Much like version control and other things that make the life of a coder easier, but aren't actually part of "Computer Science".

Re: Learning C with gdb

#32

Post by doctorwho »

It's great for instant feedback but IMHO interactive programming makes it easy (or at least easier) to be lazy. If you get used to coding by trial and error you'll never really understand the language or the problem you're trying to solve, you'll just keep trying things until it works. I know that's not how everyone approaches programming but I've seen it far too often to dismiss it

Re: Learning C with gdb

#33

Post by ghshephard »

jparishy wrote: post #25
geoka9 wrote: post #22

Earlier quoted context omitted.

> C compile times suck Can I ask you what you're comparing with? I can compare with C++, Scala and Go. The first two are horrible in that department when compared with C. Go's compiles are blazingly fast.

I'm not really comparing it to anything, just speaking from experience of having waited many hours waiting for C programs to compile in the past.

Isn't the job of your Makefile to require recompilation of only those source files that have changed?

I just did a random google of "how long to compile linux kernel" and came across this: https://plus.google.com/u/0/+LinusTorvalds/posts/6BxnSisp8fU

One nice excerpt:

"Total build time after make clean is about 1min, give or take 10secs. `touch include/linux/version.h` is 6 seconds to rebuild. Just doing a rebuild without touching anything is 2.7secs.

For a defconfig, it does build a godawful amount of modules :^)

'allnoconfig; make' is 16 seconds..."

Re: Learning C with gdb

#34

Post by codeinthehole »

If you enjoyed this, then you'll certainly enjoy the programming chapter of 'Hacking: The Art of Exploitation' by Jon Erickson (http://en.wikipedia.org/wiki/Hacking:_The_Art_of_Exploitatio...). The first half of the book is a similar exploration of C programming using GDB to explain everything. Recommended.

Re: Learning C with gdb

#35

Post by duaneb »

stonefroot wrote: post #28
duaneb wrote: post #21

Earlier quoted context omitted.

GDB can step through instruction by instruction, and you can easily examine registers.

Can I do this with a hand-written assembly program, i.e. not necessarily one that has been compiled with as and subject to GNU default optimisations or "constraints"?

It's been many years since i've done hand-written assembly, so I can't say for sure, but it should be able to do instruction stepping on arbitrary programs.

Re: Learning C with gdb

#36

Post by mhurron »

sliverstorm wrote: post #31
jobu wrote: post #24

Earlier quoted context omitted.

This is an area where many college professors fall short. In my intro to CS class we learned C, and the professor explicitly told us to debug our code with printf statements. It wasn't until my first job that I even found out about gdb. I can't believe how much time I wasted trying to debug C and C++ code in college with nothing more than printf and cout.

gdb being a utility, I believe the student is generally expected to learn it on their own if they like. Much like version control and other things that make the life of a coder easier, but aren't actually part of "Computer Science".

A course learning C is not a course in debugging or learning any particular debugger. When you are just learning the language, printf is probably the best way to do it.

On the other hand, a follow-up course on actual debugging is probably warranted. Debugging might not be part of the Science bit of Computer Science but it is on the practical end of the Computer bit which you'll probably run into doing the Science bit.

Re: Learning C with gdb

#38

Post by mmsmatt »

jobu wrote: post #24
dkhenry wrote: post #10

GDB skills are one of those super useful abilities that you just can't find in most CS graduates. I often spend a few days with new C developers just teaching them how to use GDB to find problems. They are amazed when they find out you can examine variables and set conditional breakpoints.

This is an area where many college professors fall short. In my intro to CS class we learned C, and the professor explicitly told us to debug our code with printf statements. It wasn't until my first job that I even found out about gdb. I can't believe how much time I wasted trying to debug C and C++ code in college with nothing more than printf and cout.

From the article: "The plan for this section is to write a simple program and then poke it in gdb until arrays start to make sense."

I poked arrays and pointers with printf() for too long before they started to make sense, would have loved an early introduction to debuggers!

Re: Learning C with gdb

#39

Post by scott_s »

jobu wrote: post #24
dkhenry wrote: post #10

GDB skills are one of those super useful abilities that you just can't find in most CS graduates. I often spend a few days with new C developers just teaching them how to use GDB to find problems. They are amazed when they find out you can examine variables and set conditional breakpoints.

This is an area where many college professors fall short. In my intro to CS class we learned C, and the professor explicitly told us to debug our code with printf statements. It wasn't until my first job that I even found out about gdb. I can't believe how much time I wasted trying to debug C and C++ code in college with nothing more than printf and cout.

Depends on the course and instructors. I wrote this as a TA for our Computing Systems class: http://courses.cs.vt.edu/~cs3214/fall2011/projects/esh3-debu...

When students came to me for help, my first two questions were always "What does gdb say?" and "What does valgrind say?" If they couldn't answer, I'd tell them to go find out.

Re: Learning C with gdb

#40

Post by jeremyjh »

sliverstorm wrote: post #31
jobu wrote: post #24

Earlier quoted context omitted.

This is an area where many college professors fall short. In my intro to CS class we learned C, and the professor explicitly told us to debug our code with printf statements. It wasn't until my first job that I even found out about gdb. I can't believe how much time I wasted trying to debug C and C++ code in college with nothing more than printf and cout.

gdb being a utility, I believe the student is generally expected to learn it on their own if they like. Much like version control and other things that make the life of a coder easier, but aren't actually part of "Computer Science".

Yes but I don't even remember being told it existed. My intro to C professor made sure we knew that Vi and Emacs existed and gave us enough information to be interested in learning more; why not gdb? My guess is he probably didn't use it.
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