0xDEADBEEF vs. NULL

Question

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

memset(ptr,NULL,size);

Or with 0xDEADBEEF...

memset(ptr,0xDEADBEEF,size);

1. What are the advantages to using each one, and what is the generally preferred way to achieve this in C/C++?
2. If a pointer was assigned a value of 0xDEADBEEF, couldn't it still deference to valid data?

Answer 1

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.

Answer 2

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

Answer 3

http://en.wikipedia.org/wiki/Hexspeak

These "magic" numbers are are a debugging aid to identify bad pointers, uninitialized memory etc. You want a value that is unlikely to occur during normal execution and something that is visible when doing memory dumps or inspecting variables. Initializing to zero is less useful in this regard. I would guess that when you see people initialize to zero it is because they need to have that value at zero. A pointer with a value of 0xDEADBEEF could point to a valid memory location so it's a bad idea to use that as an alternative to NULL.

Answer 4

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.