Explicitly initialize DWORD to 1, but debugger shows wildly out of range value

Question

I'm a bit flabberghasted with this issue - in debug mode this issue doesn't come up at all, but in release mode it feels like there's almost nothing I can do to fix it.

Here's a screenshot of what's going on inside VS2013:

I initialize nResult to 1L, and the internal value is shown as 3422785012. In Debug mode, this value is indeed 1L.

Any ideas as to why the displayed value isn't even close to the initial value I set for nResult? I've tried playing with compiler settings - in Debug mode this code runs fine.

Answer 1

Your code is more than likely optimized. This means that the compiler has moved and eliminated code in a way that your source code does not match what the compiler has produced.

Either debug unoptimized code, or debug optimized code with the full knowledge that the source may not match the actual instructions being performed.

If you want to debug a release build but see the correct values in the debugger, go to the Properties of your project in Visual Studio, go to the C/C++ section, and disable the optimizations. Rebuild.

Answer 2

Debugging release code is quite difficult as the compiler will reorder, remove, inline and rearrange things.

The only reliable way to debug a "release" build is to leave all release options enabled, but disable code optimizations. Or you could just disable optimizations in any modules you want full debugging info from. I've seen this done in the past when a bug was impossible to track down in a fully optimized released x64 build, as x64 clobbers the parameters far more often than x86 (when looking at crash dumps).