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Visual Studio 2008 C++ misreporting memory address location

Answer 1

+1 A:

The debugger inserts extra space. This space is set to a pre-defined value, and if it's changed, the debugger knows that something has gone wrong. It's normal for compilers and debuggers to insert space that serves no apparent purpose.

If you have used a fixed-size char[], that immediately signals to me as a problem, since there's no explicit encapsulation. You could use a custom array type (such as boost::array) to write your own buffer overrun detection code. If you throw at this time, you will get a stack trace.

DeadMG 2010-09-21 15:33:00

It's a mix of C/C++ code - the project works in Visual Studio 6.0. We've moved the code to VS2008, and now the debugger isn't displaying things correctly.

MattLear 2010-09-21 15:33:51

@MattLear: The first thing to do is update your compiler. VS6.0 is notorious, and not in a good way. There's a perfectly fine chance that you just found a bug. Secondly, you've really got to start posting about the C parts of your code, but I'm guessing that you didn't instantiate a class in that section, so my post still applies. Edit: Wait, your OP says that you're in VS9. What compiler are you using, exactly?

DeadMG 2010-09-21 15:35:06

@DeadMG - hear hear. VC6 runs stuff 'OK' and then new compiler uncovers simple bugs. I've seen this too. Also for use of boost::array or scoped_array

Steve Townsend 2010-09-21 15:37:50

DeadMG: Code was originally developed using VS 6.0 C++. We have migrated project to VS2008 C++ and it compiles with no errors (yes, lots of warnings, and yes, I know they can be a problem). I guess I'm still trying to understand how the VS memory tool can misreport memory locations?

MattLear 2010-09-21 15:41:18

DeadMG 2010-09-21 16:52:46

@DeadMG and @Steve - I'll try and upload some of the C code to better illustrate what I'm working with. I understand that the debugger may pad space, but if that's the case, I should still be able to see a variable's data change correctly. In this case, for a char[128], I see the data change at element 14, and then carries over to the next contiguous memory block (which holds an int variable and another fixed char array). Years of Java coding has apparently eroded my pointer skillset! I appreciate the responses - really!

MattLear 2010-09-21 17:55:05

Answer 2

A:

This is (probably) not going to fix your bug, but I would try to avoid C-style arrays if you can.

Unless you have some compelling reason to use the fixed-length arrays, replace them with std::vector which will be filled with 0x00 by default.

so instead of

const size_t MYCLASS::BUFLEN(16);

    class myClass {
    public:
      myClass()
      {
        memset(buffer, 0, BUFLEN);
      }
    private:
      static const size_t BUFLEN;
      char buffer[BUFLEN];
    };

you have

const size_t MYCLASS::BUFLEN(16);

    class myClass {
    public:
      myClass() : buffer(BUFLEN)
      {
        memset(buffer, 0, BUFLEN);
      }
    private:
      static const size_t BUFLEN;
      std::vector<char> buffer;
    };

Steve Townsend 2010-09-21 15:35:12

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Visual Studio 2008 C++ misreporting memory address location

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