Alex Rivera | Logout

Of Memory Management, Heap Corruption, and C++

Asked 2008-08-11T04:52:50.800
20

So, I need some help. I am working on a project in C++. However, I think I have somehow managed to corrupt my heap. This is based on the fact that I added an std::string to a class and assigning it a value from another std::string:

std::string hello = "Hello, world.\n";
/* exampleString = "Hello, world.\n" would work fine. */
exampleString = hello;

crashes on my system with a stack dump. So basically I need to stop and go through all my code and memory management stuff and find out where I've screwed up. The codebase is still small (about 1000 lines), so this is easily do-able.

Still, I'm over my head with this kind of stuff, so I thought I'd throw it out there. I'm on a Linux system and have poked around with valgrind, and while not knowing completely what I'm doing, it did report that the std::string's destructor was an invalid free. I have to admit to getting the term 'Heap Corruption' from a Google search; any general purpose articles on this sort of stuff would be appreciated as well.

(In before rm -rf ProjectDir, do again in C# :D)

EDIT: I haven't made it clear, but what I'm asking for are ways an advice of diagnosing these sort of memory problems. I know the std::string stuff is right, so it's something I've done (or a bug, but there's Not A Problem With Select). I'm sure I could check the code I've written up and you very smart folks would see the problem in no time, but I want to add this kind of code analysis to my 'toolbox', as it were.

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2 Answers

1

Other than tools like Boundschecker or Purify, your best bet at solving problems like this is to just get really good at reading code and become familiar with the code that you're working on.

Memory corruption is one of the most difficult things to troubleshoot and usually these types of problems are solved by spending hours/days in a debugger and noticing something like "hey, pointer X is being used after it was deleted!".

If it helps any, it's something you get better at as you gain experience.

Your memory allocation for the array looks correct, but make sure you check all the places where you access the array too.

answered 2008-08-21T19:18:44.040
0

As far as I can tell your code is correct. Assuming exampleString is an std::string that has class scope like you describe, you ought to be able to initialize/assign it that way. Perhaps there is some other issue? Maybe a snippet of actual code would help put it in context.

Question: Is exampleString a pointer to a string object created with new?

answered 2008-08-11T05:18:52.683

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