memory values in CRT

http://www.nobugs.org/developer/win32/debug_crt_heap.html

Mnemonics for remembering what each fill-pattern means:

• The newly allocated memory (0xCD) is Clean memory.
• The free()d memory (0xDD) is Dead memory.
• The guard bytes (0xFD) are like Fences around your memory

...

I called malloc(8) followed by free() and stepped through the CRT calls to see how the memory was changed. Read the columns from left to right, and you will see what values appear in memory at various stages during malloc() and free(). The call to malloc(8) returned a block at address 0x00321000, and I've included offsets from that address so that you can find out the information for one of your allocations.

Address	Offset	After HeapAlloc()	After malloc()	During free()	After HeapFree()	Comments
0x00320FD8	-40	0x01090009	0x01090009	0x01090009	0x0109005A	Win32 heap info
0x00320FDC	-36	0x01090009	0x00180700	0x01090009	0x00180400	Win32 heap info
0x00320FE0	-32	0xBAADF00D	0x00320798	0xDDDDDDDD	0x00320448	Ptr to next CRT heap block (allocated earlier in time)
0x00320FE4	-28	0xBAADF00D	0x00000000	0xDDDDDDDD	0x00320448	Ptr to prev CRT heap block (allocated later in time)
0x00320FE8	-24	0xBAADF00D	0x00000000	0xDDDDDDDD	0xFEEEFEEE	Filename of malloc() call
0x00320FEC	-20	0xBAADF00D	0x00000000	0xDDDDDDDD	0xFEEEFEEE	Line number of malloc() call
0x00320FF0	-16	0xBAADF00D	0x00000008	0xDDDDDDDD	0xFEEEFEEE	Number of bytes to malloc()
0x00320FF4	-12	0xBAADF00D	0x00000001	0xDDDDDDDD	0xFEEEFEEE	Type (0=Freed, 1=Normal, 2=CRT use, etc)
0x00320FF8	-8	0xBAADF00D	0x00000031	0xDDDDDDDD	0xFEEEFEEE	Request #, increases from 0
0x00320FFC	-4	0xBAADF00D	0xFDFDFDFD	0xDDDDDDDD	0xFEEEFEEE	No mans land
0x00321000	+0	0xBAADF00D	0xCDCDCDCD	0xDDDDDDDD	0xFEEEFEEE	The 8 bytes you wanted
0x00321004	+4	0xBAADF00D	0xCDCDCDCD	0xDDDDDDDD	0xFEEEFEEE	The 8 bytes you wanted
0x00321008	+8	0xBAADF00D	0xFDFDFDFD	0xDDDDDDDD	0xFEEEFEEE	No mans land
0x0032100C	+12	0xBAADF00D	0xBAADF00D	0xDDDDDDDD	0xFEEEFEEE	Win32 heap allocations are rounded up to 16 bytes
0x00321010	+16	0xABABABAB	0xABABABAB	0xABABABAB	0xFEEEFEEE	Win32 heap bookkeeping
0x00321014	+20	0xABABABAB	0xABABABAB	0xABABABAB	0xFEEEFEEE	Win32 heap bookkeeping
0x00321018	+24	0x00000010	0x00000010	0x00000010	0xFEEEFEEE	Win32 heap bookkeeping
0x0032101C	+28	0x00000000	0x00000000	0x00000000	0xFEEEFEEE	Win32 heap bookkeeping
0x00321020	+32	0x00090051	0x00090051	0x00090051	0xFEEEFEEE	Win32 heap bookkeeping
0x00321024	+36	0xFEEE0400	0xFEEE0400	0xFEEE0400	0xFEEEFEEE	Win32 heap bookkeeping
0x00321028	+40	0x00320400	0x00320400	0x00320400	0xFEEEFEEE	Win32 heap bookkeeping
0x0032102C	+44	0x00320400	0x00320400	0x00320400	0xFEEEFEEE	Win32 heap bookkeeping