0xDEADBEEF equivalent for 64-bit development?

Question

For C++ development for 32-bit systems (be it Linux, Mac OS or Windows, PowerPC or x86) I have initialised pointers that would otherwise be undefined (e.g. they can not immedi

Answer 1

Two 0xDEADBEEFs should be enough, I think..

Answer 2

I see several answers claiming NULL is a good choice, but I disagree.

NULL is often used as a valid return value from functions. It indicates a failure return or an unknown value. This is a different meaning than "uninitialized pointer."

Using a debugger on the code and seeing NULL would then leave two possibilities: the pointer was never initialized or it had failed a memory allocation.

Setting the uninitialized pointer to 0xDEADBEEF or the 64-bit equivalent means that a NULL pointer indicates an intentional value.

Answer 3

Most current 64-bit systems let you use only the lowest 2⁴⁸–2⁵² bits of the address space; higher bits of the address must be all-zero. Some chips (e.g. amd64) also let you use the highest 2⁴⁸–2⁵². Addresses outside these ranges cannot ever be mapped to accessible memory; the hardware simply won't allow it.

I therefore recommend you use a value close to 2⁶³, which is nowhere near either of the possibly-usable spaces. If the leading four hex digits are 7ff8, the value will be a double precision floating-point NaN, which is convenient. So my suggested cute hexadecimal phrase is 0x7FF8BADFBADFBADF.

By the way, you really don't want to use a value close to 0, because that makes it hard to tell an offset dereference of NULL — a structure member access, for instance — from a dereference of the poison pattern.

Answer 4

0x42 could work on both 32bit and 64bit ? (It should still trigger a crash since it is close enough to the NULL pointer, and given that it's rather large, chances are you would not have it within a regular dereference of a structure field with the structure pointer being NULL).

Answer 5

0xBADC0FFEE0DDF00D

Answer 6

I don't have a good choice for you, but here's a list of hex words that you can use to make your phrase.