They do not do the same thing. The latter printf
statement interprets b
as an unsigned int
, which is wrong, as b
is a pointer.
Pointers and unsigned int
s are not always the same size, so these are not interchangeable. When they aren’t the same size (an increasingly common case, as 64-bit CPUs and operating systems become more common), %x
will only print half of the address. On a Mac (and probably some other systems), that will ruin the address; the output will be wrong.
Always use %p
for pointers.