// The following values are non-zero,constant,odd,large,and atypical.
// * Non-zero values help find bugs that assume zero-filled data
// * Constant values are good so that memory filling is deterministic (to help
// make bugs reproducible). 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 (e.g. properly aligned pointers to types other than char are not
// odd).
// * Large byte values are less typical and are useful for finding bad addresses.
// * Atypical values (i.e.,not too often) are good because they typically cause
// early detection in code.
// * For the case of the no-man's land and free blocks,if you store to any of
// these locations,the memory integrity checker will detect it.
//
// The align_land_fill was changed from 0xBD to 0xED to ensure that four bytes of
// that value (0xEDEDEDED) would form an inaccessible address outside of the lower
// 3GB of a 32-bit process address space.
static unsigned char const no_mans_land_fill{0xFD}; // Fill unaligned no-man's land
static unsigned char const align_land_fill {0xED}; // Fill aligned no-man's land
static unsigned char const dead_land_fill {0xDD}; // Fill free objects with this

static unsigned char const clean_land_fill {0xCD}; // Fill new objects with this

更多客源参考：debug_heap.cpp