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C++ Crt Debug Heap Dev 10

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The C run-time library provides extensive debugging support. To use one of the CRT debug libraries, you must link with /DEBUG and compile with /MDd, /MTd, or /LDd.

Apr 19, 2018 Explains that you can cause a user-defined breakpoint at a specific point of memory allocation by setting crtBreakAlloc at either compile time or run-time. Describes how to use crtBreakAlloc to debug a memory allocation. Debugging Heap Corruption in Visual C 2 Heap Corruption Heap corruption is an undesired change in the data allocated by your program. Its symptoms include: System errors, such as access violations. Unexpected data in program output. Unexpected paths of program execution. Your program may show a symptom of heap corruption immediately or may.

Aug 04, 2012  Getting started with Windows GDI graphics applications in C Andy 4 August 2012 C / MFC / STL, Windows No Comments A guide to getting started with Windows graphics applications for the very first time. The Windows Graphics Device Interface (GDI) forms the basis of drawing lines and objects, and from this device contexts. May 13, 2001  The rest of my examples will assume you have included this command first, and will not preface commands as such. So now we have a program that initialises GDI+, this is probably a good place to discuss how GDI+ actually works. As you may be aware, GDI works with the concept of a device context. Typically you would draw a box using GDI like this. Dev-C Using GDI and GradientFill From: Dave McMinn - 2004-07-20 22:26:24. Hello, Has anyone managed to successfully use GradientFill from Win32 gdi32.dll in any DevC/gcc programs? It doesn't appear to be in the import library and pexports crashes generating a def file for gdi32.dll. I don't want to have to fill in. C++ dev gdi 2. GDI objects selected in a DC can't be deleted - even when you call DeleteObject. This handy class makes these potential leaks a thing of the past. GDI provides the most basic access to the display, via C calls only (no classes or any other OO stuff) and dates back to Windows 2.0. GDI+ is more modern and has some improved capabilities, but it's still a.

Remarks

The main definitions and macros for CRT debugging can be found in the CRTDBG.h header file.

The functions in the CRT debug libraries are compiled with debug information (/Z7, /Zd, /Zi, /ZI (Debug Information Format)) and without optimization. Some functions contain assertions to verify parameters that are passed to them, and source code is provided. With this source code, you can step into CRT functions to confirm that the functions are working as you expect and check for bad parameters or memory states. (Some CRT technology is proprietary and does not provide source code for exception handling, floating point, and a few other routines.)

For more information on the various run-time libraries you can use, see C Run-Time Libraries.

See also

23 Sep 2015CPOL
By default, Visual Studio (up to VS 2013) uses additional debug heap that slows down applications, even in Release mode. Read what you can do about this.

Introduction

Some time ago, I was tracing a perf problem (UI code + some custom logic). I needed to track what module was eating most of the time in one specific scenario. I prepared the release version of the app and I added some profiling code. I’ve used Visual Studio 2013. The app used OutputDebugString so I needed to run the debugging (F5) in order to be able to see logs in the output window (I know I know, I could use DebugView as well…)

But, my main assumption was that when I run F5 in release mode, only a little performance hit would occur. What was my astonishment when I noticed it was a wrong idea! My release-debug session pointed to a completely different place in the code…

Story Continuation

What was wrong with the assumption? As it appeared when I was starting the app with F5, even in release mode Visual Studio is attaching a special debug heap! The whole application runs slower, because every system memory allocation gets additional integrity checks.
My code used win32 UI and thus every list addition, control creation was double checked by this special heap. When running using F5, the main bottleneck seemed to be happening in that UI code. When I disabled the additional heap checking (or when I simply run my application without debugger attached), the real bottleneck appeared in a completely different place.

Those kind of bugs have even their name Heisenbug, those are bugs that disappear (or are altered) by tools that are used to track the problem. As in our situation: debugger was changing the performance of my application so I was not able to find a real hot spot…

Let’s learn from the situation! What is this debug heap? Is it really useful? Can we live without it?

Example

Let’s do a simple experiment:

Full code located here: fenbf/dbgheap.cpp

The above example will allocate (and delete) memory NUM_ITERS x NUM_ALLOC times.

For NUM_ITERS=100 and NUM_ALLOC=100 and NUM_ELEMENTS=100000 (~400kb per allocation) I got:

So by running using F5, we get ~3.7 slower memory allocations!

Let’s compare calls stacks:

To prepare the above images, I run the app using F5 and I paused at random position. There were lots of allocations, so I usually entered some interesting code. Of course, producing the second view (without F5) was a bit harder, so I set a breakpoint using _asm int 3 (DebugBreak() also would work), then I got debugger attached so I could also pause at random. Additionally, since the second version runs much faster, I needed to increase the number of allocations happening in the program.

Running with F5, I could easily break in some deep allocation method (and as you can see, there is a call to ntdll.dll!_RtlDebugAllocateHeap@12 ()). When I attached debugger (the second call stack) I could only get into vector allocation method (STD).

Debug Heap

All dynamic memory allocation (new, malloc, std containers, etc. etc.) at some point must ask system to allocate the space. Debug Heap adds some special rules and ‘reinforcements’ so that memory will not be corrupt.
It might be useful when coding in raw C winApi style (when you use raw HeapAlloc calls), but probably not when using C++ and CRT/STD.

CRT has its own memory validation mechanisms (read more at msdn) so windows Debug Heap is doing additional, mostly redundant checks.

Options

What can we do about this whole feature? Fortunately, we have an option to disable it!

Any drawbacks of this approach?

Obviously, there is no additional checking… but since you’ve probably checked your app in Debug version, and since there are additional checks in CRT/STD, no problems should occur.

Also, in the latest Visual Studio 2015, this feature is disabled by default (it is enabled in the previous versions). This suggests that we should be quite safe.

On the other hand, when you rely solely on WinAPI calls and do some advanced system programming, then DebugHeap might help…

Summary

Things to remember:
Use '_NO_DEBUG_HEAP' to increase performance of your debugging sessions!.

C Crt Debug Heap Dev 10 Software

As I mentioned in the beginning, I was quite surprised to see such different results when running F5 in release mode VS running the app alone. Debugger usually adds some performance hit, but not that huge! I can expect a slow down in a debug build, but not that much in release version of the application.

Debug Heap is attached every time: in debug builds and in release as well. And it’s not that obvious. At least we can disable it.

C++ Crt Debug Heap Dev 10 Key

Fortunately Debug Heap is disabled by default in Visual Studio 2015 - this shows that MS Team might be wrong when they enabled Debug Heap by default in the previous versions of Visual Studio.

Resources

  • Books on Visual Studio: Professional Visual Studio 2015, Ivor Horton's Beginning Visual C++ 2013
  • ofekshilon.com: Accelerating Debug Runs, Part 1: _NO_DEBUG_HEAP - detailed information about this feature
  • VC++ team blog: C++ Debugging Improvements in Visual Studio 2015
  • preshing.com: The Windows Heap Is Slow When Launched from the Debugger
  • informit.com: Advanced Windows Debugging: Memory Corruption Part II—Heaps
  • MSDN blogs: Anatomy of a Heisenbug

C Crt Debug Heap Dev 10 Key

History

  • 23rd September, 2015 - Initial version

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