Visual C++: Difference between Start with/without debugging in Release mode

visual-studio debugging visual-c++ release
Ashwin Nanjappa picture Ashwin Nanjappa · Jul 29, 2010 · Viewed 9.6k times · Source

What is the difference between Start Debugging (F5) and Start without Debugging (CTRL-F5) when the code is compiled in Release mode?

I am seeing that CTRL-F5 is 10x faster than F5 for some C++ code. If I am not wrong, the debugger is attached to the executing process for F5 and it is not for CTRL-F5. Since this is Release mode, the compiled code does not have any debugging information. So, if I do not have any breakpoints, the execution times should be the same across the two, isn't it?!

(Assume that the Release and Debug modes are the typical configurations you get when you create a new Visual C++ project.)

Answer

JBH picture JBH · Dec 7, 2010

The problem is that Windows drops in a special Debug Heap, if it detects that your program is running under a Debugger. This appears to happen at the OS level, and is independent of any Debug/Release mode settings for your compilation.

You can work around this 'feature' by setting an environment variable: _NO_DEBUG_HEAP=1

This same issue has been driving me nuts for a while; today I found the following, from whence this post is derived: http://blogs.msdn.com/b/larryosterman/archive/2008/09/03/anatomy-of-a-heisenbug.aspx

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