I need to debug a C program that includes posix threads, socket programming (udp client, server). I use ubuntu 12.04 and as IDE/SDK, Qt Creator 2.4.1 and Netbeans IDE 7.1.2. I know they use gdb for debugging.
When I start to debug my program, the program stops running after 5 min or so and neither Qt Creator or Netbeans output any error or warning, although I use debugging feature and my program suppose to listen for a UDP port.
I use printf for all line of my code, and I can see that my program works as it suppose to and listen the UDP port and waits. I can not figure the problem out why it stops without any reason and since IDEs that I am using do not show any debug error, warning, I can not think any reason.
I wonder if anyone can suggest me a debug program that monitors all/some variables and threads during the run time. Thank you.
An old, but reliable tool is ddd, which is basically the gdb GUI wrapper. Although, I usually do debugging directly with Emacs, ddd is the tool that you'll be able to run on almost all *nix platforms.
gdb isn't too comfortable but always available.
To do runtime analysis of different types, especially checking memory access, Valgrind (see here for docs) might be the tool of choice.
Update: I'm referring to *IX systems. For Windows gbd also works in the cygwin enviroment. Nativly there is VC Express, which is free and includes IDE and debugger.
I'm not quite sure what debugger is used for your kind of application. The only debugger I know about on Linux is gdb. It along with printf statements is all I need.
gdb is simple, though not "too comfortable" as #alk said, but seems to be ubiquitous.
There is also Eclipse, and that's quite a nice development and debugging platform, too.
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I'm studying computer engineering and we have a class called operating systems where they lecture us about how OSes handle stuff etc. This week we were given a homework which requests us to code a shell that works on Linux. The problem is, they tought us literally nothing on how to code a shell so we are supposed to do some research and figure it out.
I found this guide online and it seemed perfect to me: link
Code, with explanations, what else could I ask for.
Now, I'm using a Windows PC and I use Dev-C++ IDE with GCC compiler. Can I code a shell that works on Linux with my current setup or do I have to install Linux? Are there any major differences between how shells run on these OSes?
If you want to write a shell for Linux, you want to target GNU/Linux which is basically POSIX with some extensions.
Dev-C++ by default uses MinGW GCC as its compiler, providing a Win32 API.
Win32 and POSIX are completely and fundamentally different. A shell written for one will not even slightly resemble the other.
Instead, you have several options:
Dev-C++ can optionally use Cygwin GCC, providing a more GNU/Linux-like experience on Windows. You need to take great care not to rely on any Cygwin-specific functionality like how it automatically translates pathnames and line terminators. You'll still need access to a Linux install to verify that it works.
Windows 10 lets you install WSL, a more modern Linux compatibility layer for Windows. Dev-C++ doesn't explicitly states it support it, so you may need to edit and compile separately, and may lose debugging functionality. You'll still need access to a Linux install to verify that it works.
Just run Linux in a VM. The only thing to care about is getting your shell working.
I would suggest saving yourself a ton of trouble right now and just download/install an Ubuntu image in VirtualBox.
i am using gcc 4.4.3 on ubuntu 10.4 32bit machine.
i use 'gdb' to debug my code. Since few days i am seeing that whenever i debug code gdb steps into the c library functions used in the code also(like printf,fgets etc). This shows a long list of calls from one function to other.see the attached screen shot.
Previously gdb was working fine just stepping over my own code.
Maybe i am being novice !! But it is sometimes really irritating when gdb shows me numerous lines which i am not interested in the present context.
If someone can guide me as in how to turn off/on this feature and what can be cause of it being switched on on its own(i don't remember doing anything).
Many thanks.
i used to do that previously also but then it never went into any of the lib functions
You (or someone) have installed libc6-dbg package. Before that, GDB couldn't step into libc functions, because they didn't have any debug info. Now they do, and it can.
Either get out of the habit of typing step when you want next, or un-install libc6-dbg.
I want a debugger to debug my OS. At many places i am not being able to figure out what is wrong. So is there any debugger which can debug operating systems? can i do it with gdb?
You will need to use a solution which emulates another computer on your computer - essentially, a virtual machine. The most obvious ones which come to mind instantly are VirtualBox and VMware, but those weren't designed with debugging the machine and/or the OS.
What you're looking for is either Bochs or QEMU. Both (as far as I remember) can be integrated with gdb in order to set breakpoints and analyze the execution of your code. You might also want to read this OSdev.org article.
I primarily use Bochs for testing my OS projects. It includes a helpful debugger (bochsdbg).
A CS course I'm taking online suggests students compile their source code and run tools like valgrind on the OS UNIX. I'm completely new to UNIX, Linux, their tools, and coding in c. I've made some attempts at installing FreeBSD 8.1 on VMWare Player 3.1.3, and even managed to get VMWare Tools running. But the FreeBSD documentation has led me down many dead-ends in accomplishing common tasks i.e. mounting an NFS or USB device. It turns out that the packages I need to make this happen aren't installed or configured, and I don't see any straight answer on how to install them.
So, if I'm using UNIX only as a tool to run gcc, g++, valgrind for this CS course, and these can be run on Linux instead, it seems like I can get the job done faster using Ubuntu Linux.
Can Linux be used to compile and run c code identically on UNIX, if compiled on Linux? Or if not, what are the differences to look for?
Thanks
For the novice-level C programmer such as OP, the difference of environment is negligible. Go ahead with Linux.
I think for purposes of the course you could run your programs and tools on Linux,
but I guess the reason your teacher wants you to use FreeBSD is so that you learn other things besides just coding up your problems
The two should be effectively the same. The only major difference you might see would be due to different versions being used. I would check to see what versions of gcc, g++ and valgrind the teacher is having you use, and make sure that you have the same version running on your install of Linux.
You can also use MinGW or Cygwin. You mentioned VMWare, so I'm guessing you're trying to just get an environment up and running in a windows environment. They both allow you to use the compiler and some of the tools without a full install of a Linux based system. In a CS course they would be more than enough.
The main differences too look for:
Compiling C / C++ is not machine independent. You need to have a small environment to compile on UNIX anyway if you need to submit compiled programs to your professor.
C / C++ is rather portable if you don't use anything that's non-portable. It's very hard to verify that you didn't use something that's different between the two machines, so you may wish to compile on UNIX to verify you didn't let an unavailable library (or an specific to the OS procedure, argument, behavior, bugs, etc.) slip into your code.
The vendor of make between the two machines may differ. This means that while the core of make will operate similarly, certain features might not be available in both. In reality, you probably won't use most of makes extended features, but in a worst case scenario you might opt to maintain multiple Makefiles or limit yourself to a common subset of features.
At the end of the day, it all boils down to what your professor will want. Odds are 95+% that you can do 100% of the work in Linux, but the prof's requirements or grading environment might be such that you will have to copy your code into a UNIX account to build the final "submission" executable. Considering that university UNIX accounts aren't nearly as portable as Linux on a laptop, the cost of the "final verification / porting" to the University computer is likely to be small compared to the convenience of working on your homework more hours than you can manage in a fixed lab.
I have learned C and I would like to start to improve open source software. I would like to hack away one irritating bug in GTK+. To see the bug I need to use Gedit.
How can I download the sources of GTK+ and gedit and compile both of them so that I can see where the bug is? And I have never used any debugger in Linux so is there somewhere a tutorial for that?
You can get information about downloading and compiling of gedit here:
http://projects.gnome.org/gedit/developers.html
My Debugger of choice is GDB:
http://www.gnu.org/software/gdb/
GDB is a console application that may be hard to handle for a beginner. Try an IDE like Eclipse that provides a GUI to GDB.
Almost all Linux debuggers are front-ends for or adaptations of the gdb debugger. You should therefore learn how to use this first, preferably by starting on
small programs of your own construction, not giant FOSS codebases. The gdb manual,
available from here is actually a pretty good tutorial.
The information on building and installing GTK+ should be here:
http://www.gtk.org/development.html
The sources should be here:
http://www.gtk.org/download-linux.html
You can check out gdb:
http://www.gnu.org/software/gdb/ That's a pretty standard linux debugger. I would spend time with it on something simple first, or get an IDE that uses it. Learning gdb can be worth the time though.
gdb is a dinosaur which should long since have been made extinct. Debugging is one area where (gasp!) Windows beats Unix. Having got that off my chest, I advise you to start with the Data Display Debugger (DDD) graphical front end to gdb. Yes, the GUI is quaint, but you will be far more productive, quicker, than if you start with gdb.
Also don't overlook valgrind for finding and diagnosing memory errors. The KDE project actually mandates use of valgrind; I'm not sure about Gnome.
It is possible that you won't see the bug if you download the latest gedit and gtk+ sources. It might be fixed in the latest sources or the latest sources might be different enough to not trigger your bug.
What Linux distribution are you running?
First of all I'd suggest consulting your distribution's bug database to see if someone has filed a similar bug. If you don't find anything, I'd suggest using your distribution's tools to obtain the source that corresponds to the binary that you have installed on your sytem (e.g. apt-get source libgtk-2.0 on Debian or Ubuntu).
Also, your distribution might also make a debug package available (e.g. libgtk2.0-0-dbg on Debian) which will let you run a debugger on the binary that you already have without requiring the source. While this is no substitute for having the sources, it can be useful for running valgrind or making sense out of a core file.