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Learning C with gdb

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Re: Learning C with gdb

#61

Post by breckinloggins »

Also cool to play around with are the various options that let GCC (and presumably LLVM) show you the various compilation stages of your C code. You can even spit out the C and resulting assembly side-by-side.

I haven't had the time to play with this, but Part 4 of the excellent "Unix as IDE" series [1] goes into it and I'm sure there's more around the web.

Another really fun way to get into the underlying assembler that the C compiler generates is Vidar Hokstad's "Writing a compiler in Ruby, bottom up" [2]. This series involves writing little C functions, compiling them to the simplest assembly you can get, then writing a ruby compiler (in Ruby!) that emits that assembly. Some people have objections to the approach, but it's really quite nifty. I especially like it because it's really refreshing to see a compiler tutorial that doesn't start with the lexer and parser.

[1] http://blog.sanctum.geek.nz/unix-as-ide-compiling/ [2] http://www.hokstad.com/compiler

Re: Learning C with gdb

#62

Post by winter_blue »

The visual debugger in both Eclipse CDT and Visual C++ let you do things like create breakpoints, step through your program, monitor variable values, even create conditional breakpoints that are triggered when a particular lineof code is executed n number of times or when some particular expression involving variables in the local context of the breakpoint turn true.

My question is, what advantages do you get in using gdb directly through the CLI rather than through an IDE? (like Eclipse/NetBeans which itself uses gdb for C/C++ debugging, but has a nice graphical UI for it.)

Re: Learning C with gdb

#63

Post by stcredzero »

SAHChandler wrote: post #49
stcredzero wrote: post #6

There was a debugger posted here to HN awhile back that actually displayed structs and pointers graphically. What was the name of that project, and is it still around? I was trying to find it the other day. I thought that was a dynamite tool for students. With LLVM, we should be able to have a REPL for C. as a pedagogical tool.

I believe it was Tenacious-C: http://tenaciousc.com/

Yes, that was it! We have a winner! (A wiener?)

Re: Learning C with gdb

#64

Post by lysol »

16s wrote: post #13

gdb is very nice. I use it with C++ too. Watch sizeof on char arrays. Why is my string's sizeof always 8? That confuses some when starting out.

That's because sizeof is for the size of the variable (a char pointer), not the size of the string up to the null terminator, which is what strlen's for.

Re: Learning C with gdb

#65

Post by IsTom »

winter_blue wrote: post #62

The visual debugger in both Eclipse CDT and Visual C++ let you do things like create breakpoints, step through your program, monitor variable values, even create conditional breakpoints that are triggered when a particular lineof code is executed n number of times or when some particular expression involving variables in the local context of the breakpoint turn true. My question is, what advantages do you get in usin…

I'm not sure if CDT and Visual C++ can't do that, but I don't think so: gdb can attach to already running processes. Saved me once from a bug in ruby runtime.

Re: Learning C with gdb

#66

Post by greenyoda »

IsTom wrote: post #65
winter_blue wrote: post #62

The visual debugger in both Eclipse CDT and Visual C++ let you do things like create breakpoints, step through your program, monitor variable values, even create conditional breakpoints that are triggered when a particular lineof code is executed n number of times or when some particular expression involving variables in the local context of the breakpoint turn true. My question is, what advantages do you get in usin…

I'm not sure if CDT and Visual C++ can't do that, but I don't think so: gdb can attach to already running processes. Saved me once from a bug in ruby runtime.

The Visual C++ debugger can attach to a running process. I've used that feature to debug server code.

Re: Learning C with gdb

#67

Post by kevinnk »

scott_s wrote: post #39
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.

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.

Yeah, GDB and Valgrind are heavily encouraged at the University of Michigan in both introductory and advanced classes. Talking to friends at other universities, it seems like most other places encourage it too.

Re: Learning C with gdb

#69

Post by fferen »

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.

I guess it depends on the college. My ECE intro to programming class taught gdb very early, basically right after we learned the basics of C. I thought it was pretty neat but it never really seemed like a huge advantage over printing, especially after I wrote a few logging macros.

Re: Learning C with gdb

#70

Post by kevinnk »

winter_blue wrote: post #62

The visual debugger in both Eclipse CDT and Visual C++ let you do things like create breakpoints, step through your program, monitor variable values, even create conditional breakpoints that are triggered when a particular lineof code is executed n number of times or when some particular expression involving variables in the local context of the breakpoint turn true. My question is, what advantages do you get in usin…

GDB itself has a -tui option which gives you a nice "gui" style interface in the command line. As to why you would not use any sort of gui interface, I don't think the command line alone gives you any advantage as far as I know.
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