In Visual Studio C++, what are the memory allocation representations?

Question

In Visual Studio, we've all had "baadf00d", have seen seen "CC" and "CD" when inspecting variables in the debugger in C++ during run-time.

From what I understand, "CC" is in DEBUG mode only to indicate when a memory has been new() or alloc() and unitilialized. While "CD" represents delete'd or free'd memory. I've only seen "baadf00d" in RELEASE build (but I may be wrong).

Once in a while, we get into a situation of tacking memory leaks, buffer overflows, etc and these kind of information comes in handy.

Would somebody be kind enough to point out when and in what modes the memory are set to recognizable byte patterns for debugging purpose?

When and why will an OS initialise memory to 0xCD, 0xDD, etc. on malloc/free/new/delete? — phuclv
@Lưu Vĩnh Phúc : It's not the OS, it's the debugger. The "D" (as on 0xCD and 0xDD) is for Debug (i.e. malloc_dbg is what gets called via malloc as explained in msdn.microsoft.com/en-us/library/aa270812(v=vs.60).aspx). I believe it also adds fence/posts around the heaps for tracking buffer-overruns. It's quite useful to catch issues when you have a bug of double-delete or multiple-free (or even possible calling of delete instead of delete[]) and dangling pointers which has been disposed and when you inspect the data, it's "0xDD" (or when uninitialized heap shows 0xCD) — HidekiAI
I didn't say thay it's the OS. It's the other asker that wrote the tittle incorrectly — phuclv
Possible duplicate of When and why will an OS initialise memory to 0xCD, 0xDD, etc. on malloc/free/new/delete? — phuclv

Mark Ingram Mark Ingram · Accepted Answer · 2008-09-24T14:14:34

This link has more information:

https://en.wikipedia.org/wiki/Magic_number_(programming)#Debug_values

* 0xABABABAB : Used by Microsoft's HeapAlloc() to mark "no man's land" guard bytes after allocated heap memory
* 0xABADCAFE : A startup to this value to initialize all free memory to catch errant pointers
* 0xBAADF00D : Used by Microsoft's LocalAlloc(LMEM_FIXED) to mark uninitialised allocated heap memory
* 0xBADCAB1E : Error Code returned to the Microsoft eVC debugger when connection is severed to the debugger
* 0xBEEFCACE : Used by Microsoft .NET as a magic number in resource files
* 0xCCCCCCCC : Used by Microsoft's C++ debugging runtime library to mark uninitialised stack memory
* 0xCDCDCDCD : Used by Microsoft's C++ debugging runtime library to mark uninitialised heap memory
* 0xDDDDDDDD : Used by Microsoft's C++ debugging heap to mark freed heap memory
* 0xDEADDEAD : A Microsoft Windows STOP Error code used when the user manually initiates the crash.
* 0xFDFDFDFD : Used by Microsoft's C++ debugging heap to mark "no man's land" guard bytes before and after allocated heap memory
* 0xFEEEFEEE : Used by Microsoft's HeapFree() to mark freed heap memory

In Visual Studio C++, what are the memory allocation representations?

3 Answers