0xDEADBEEF vs. NULL

Question

Throughout various code, I have seen memory allocation in debug builds with NULL...

memset(ptr,NULL,size);

Or with 0xDEA

Answer 1

One reason that you null the buffer or set it to a special value is that you can easily tell whether the buffer contents is valid or not in the debugger.

Dereferencing a pointer of value "0xDEADBEEF" is almost always dangerous(probably crashes your program/system) because in most cases you have no idea what is stored there.

Answer 2

DEADBEEF is an example of HexSpeek. With it, as a programmer you convey intentionally an error condition.

Answer 3

I would definitely recommend 0xDEADBEEF. It clearly identifies uninitialized variables, and accesses to uninitialized pointers.

Being odd, dereferencing a 0xdeadbeef pointer will definitely crash on the PowerPC architecture when loading a word, and very likely crash on other architectures since the memory is likely to be outside the process' address space.

Zeroing out memory is a convenience since many structures/classes have member variables that use 0 as their initial value, but I would very much recommend initializing each member in the constructor rather than using the default memory fill. You will really want to be on top of whether or not you properly initialized your variables.

Answer 4

Vote me down if this is too opinion-y for StackOverflow but I think this whole discussion is a symptom of a glaring hole in the toolchain we use to make software.

Detecting uninititialized variables by initializing memory with "garabage-y" values detects only some kinds of errors in some kinds of data.

And detecting uninititialized variables in debug builds but not for release builds is like following safety procedures only when testing an aircraft and telling the flying public to be satisfied with "well, it tested OK".

WE NEED HARDWARE SUPPORT for detecting uninitialized variables. As in something like an "invalid" bit that accompanies every addressability entity of memory (=byte on most of our machines) and which is set by the OS in every byte VirtualAlloc() (et. al, or equivalents on other OS's) hands over to applications and which is automatically cleared when the byte is written to but which causes an exception if read first.

Memory is cheap enough for this and processors are fast enough for this. This end of reliance on "funny" patterns and keeps us all honest to boot.