What could be causing this crash?

Question

I have a C++ program (GCC) and when I add one or more int members to an abstract base class, the program starts crashing. In the case I've exampled, it seems that by adding this member, a member in a derived class quits getting initialized (or gets stomped on at some point). If I add more members, it starts (not) working different. This is all really odd because the member is never used anywhere. I can comment out that one line and the program recompile just fine and runs without error.

The whole program is ~3KLOC and would be very hard to strip down.

I'm totally at a loss as to where to start looking. Any Ideas?

---

Update

I found the issue: free-ing malloc-ed memory and delete-ing new-ed memory is not safe in the same program.

Answer 1

A little more information about the crash would be helpful, as there are mulitple ways a program can crash. However, the first thing I do on Linux if I suspect it could be a memory error is to run the program through Valgrind (Memcheck) and see what it can tell me.

Also as a shot in the dark, is your build system generating dependencies correctly? One possibility is that your modifying the abstract class but not recompiling all the source files which depend on the abstract class, which could be problematic.

Answer 2

Off the top of my head, without seeing any code (see comments on your question) I would suggest a rogue pointer which normally stomps on something you don't notice, but introducing a new member makes it stomp on something you do notice.

Try adding members of different sizes, or more (unused) int members, or maybe a string in the form: const char xxx[50]; to reserve more space.

Answer 3

99 times out of 100 I find that if you change the data structure of a class and you start getting weird crashes then the build dependencies are not quite right i.e. you need to rebuild something that for some reason is not getting rebuilt.

If it's not a major pain to completely clean and rebuild your entire project then I would give that a go and then we can rule this answer out.

Answer 4

Try running your program in gdb.

gdb your_executable

Then hit 'r' then enter when your code crashes you can hit 'bt' then enter to see the offending line of code.

Answer 5

After you changed the class did you re-compile all the source?

If you only re-compiled the base or derived class (not sure where you put the new int) then all the other objects have the wrong size for your class. You need to delete all the object files and re-build them.