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Debugging Best Practices for C++ STL/Boost with gdb

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c++

stl

boost

gdb

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Does GDB slow down?

GDB does software watchpointing by single-stepping your program and testing the variable's value each time, which is hundreds of times slower than normal execution. (But this may still be worth it, to catch errors where you have no clue what part of your program is the culprit.)

Can you use GDB with C++?

You can use GDB as a C++ debugger if a program is written with the GNU compiler and the -g flag. By debugging with GDB, you can catch errors and solve them before they cause severe issues.

What is GDB hardware debugging?

GDB stands for the “Gnu DeBugger.” This is a powerful source-level debugging package that lets you see what is going on inside your program. You can step through the code, set breakpoints, examine and change variables, and so on. Like most Linux tools, GDB itself is command line driven, making it rather tedious to use.


Maybe not the sort of "tip" you were looking for, but I have to say that my experience after a few years of moving from C++ & STL to C++ & boost & STL is that I now spend a lot less time in GDB than I used to. I put this down to a number of things:

  • boost smart pointers (particularly "shared pointer", and the pointer containers when performance is needed). I can't remember the last time I had to write an explicit delete (delete is the "goto" of C++ IMHO). There goes a lot of GDB time tracking down invalid and leaking pointers.
  • boost is full of proven code for things you'd probably hack together an inferior version of otherwise. e.g boost::bimap is great for the common pattern of LRU caching logic. There goes another heap of GDB time.
  • Adopting unittesting. boost::test's AUTO macros mean it's an absolute doddle to set up test cases (easier than CppUnit). This catches lots of stuff long before it gets built into anything you'd have to attach a debugger to.
  • Related to that, tools like boost::bind make it easier to design-for-test. e.g algorithms can be more generic and less tied up with the types they operate on; this makes plugging them into test shims/proxies/mock objects etc easier (that and the fact that exposure to boost's template-tasticness will encourage you to "dare to template" things you'd never have considered before, yielding similar testing benefits).
  • boost::array. "C array" performance, with range checking in debug builds.
  • boost is full of great code you can't help but learn from

You might look at:

Inspecting standard container (std::map) contents with gdb


I think the easiest and most option is to use logging (well I actually use debug prints, but I think that's not a point). The biggest advantage is that you can inspect any type of data, many times per program execution and then search it with a text editor to look for interesting data. Note that this is very fast. The disadvantage is obvious, you must preselect the data which you want to log and places where to log. However, that is not such a serious issue, because you usually know where in the code bad things are happening (and if not, you just add sanity checks here and there and then, you will know).

Checked/debug libraries are good, but they are better as a testing tool (eg. run it and see if I'm doing anything wrong), and not as good at debugging a specific issue. They can't detect a flaw in user code.

Otherwise, I use plain GDB. It is not that bad as it sounds, although it might be if you are scared by "print x" printing a screenful of junk. But, if you have debugging information, things like printing a member of a std::vector work and if anything fails, you still can inspect the raw memory by the x command. But if I know what I'm looking for, I use option 1 - logging.

Note that the "difficult to inspect" structures are not only STL/Boost, but also from other libraries, like Qt/KDE.