何时以及为什么操作系统会在malloc/free/new/delete上将内存初始化为0xCD,0xDD等？

我知道操作系统有时会使用某些模式(如0xCD和0xDD)初始化内存.我想知道的是何时以及为什么会发生这种情况.

什么时候

这是否特定于编译器使用？

对于这个,malloc/new和free/delete的工作方式是否相同？

它是特定于平台的吗？

它会出现在其他操作系统上,例如Linux或VxWorks吗？

为什么

我的理解是这只发生在Win32调试配置中,它用于检测内存溢出并帮助编译器捕获异常.

你能举一个关于这个初始化如何有用的实际例子吗？

我记得读过一些东西(可能在Code Complete 2中),在分配内存时将内存初始化为已知模式是好的,某些模式会触发Win32中的中断,这将导致调试器中出现异常.

这有多便携？

快速总结一下,当编译为调试模式时,Microsoft编译器用于各种无主/未初始化内存的位置(支持可能因编译器版本而异):

Value     Name           Description 
------   --------        -------------------------
0xCD     Clean Memory    Allocated memory via malloc or new but never 
                         written by the application. 

0xDD     Dead Memory     Memory that has been released with delete or free. 
                         Used to detect writing through dangling pointers. 

0xED or  Aligned Fence   'No man's land' for aligned allocations. Using a 
0xBD                     different value here than 0xFD allows the runtime
                         to detect not only writing outside the allocation,
                         but to also detect mixing alignment-specific
                         allocation/deallocation routines with the regular
                         ones.

0xFD     Fence Memory    Also known as "no mans land." This is used to wrap 
                         the allocated memory (surrounding it with a fence) 
                         and is used to detect indexing arrays out of 
                         bounds or other accesses (especially writes) past
                         the end (or start) of an allocated block.

0xFD or  Buffer slack    Used to fill slack space in some memory buffers 
0xFE                     (unused parts of `std::string` or the user buffer 
                         passed to `fread()`). 0xFD is used in VS 2005 (maybe 
                         some prior versions, too), 0xFE is used in VS 2008 
                         and later.

0xCC                     When the code is compiled with the /GZ option,
                         uninitialized variables are automatically assigned 
                         to this value (at byte level). 


// the following magic values are done by the OS, not the C runtime:

0xAB  (Allocated Block?) Memory allocated by LocalAlloc(). 

0xBAADF00D Bad Food      Memory allocated by LocalAlloc() with LMEM_FIXED,but 
                         not yet written to. 

0xFEEEFEEE               OS fill heap memory, which was marked for usage, 
                         but wasn't allocated by HeapAlloc() or LocalAlloc(). 
                         Or that memory just has been freed by HeapFree(). 

/*
 * The following values are non-zero, constant, odd, large, and atypical
 *      Non-zero values help find bugs assuming zero filled data.
 *      Constant values are good so that memory filling is deterministic
 *          (to help make bugs reproducable).  Of course it is bad if
 *          the constant filling of weird values masks a bug.
 *      Mathematically odd numbers are good for finding bugs assuming a cleared
 *          lower bit.
 *      Large numbers (byte values at least) are less typical, and are good
 *          at finding bad addresses.
 *      Atypical values (i.e. not too often) are good since they typically
 *          cause early detection in code.
 *      For the case of no-man's land and free blocks, if you store to any
 *          of these locations, the memory integrity checker will detect it.
 *
 *      _bAlignLandFill has been changed from 0xBD to 0xED, to ensure that
 *      4 bytes of that (0xEDEDEDED) would give an inaccessible address under 3gb.
 */

static unsigned char _bNoMansLandFill = 0xFD;   /* fill no-man's land with this */
static unsigned char _bAlignLandFill  = 0xED;   /* fill no-man's land for aligned routines */
static unsigned char _bDeadLandFill   = 0xDD;   /* fill free objects with this */
static unsigned char _bCleanLandFill  = 0xCD;   /* fill new objects with this */