Sometimes I see programmers use:
void *ptr = <something>;
if (ptr == NULL)
<do something>;
Instead of:
void *ptr = <something>;
if (!ptr)
<do something>;
Is there anything that can go wrong with if (!ptr), or is it just a coding style preference?
In C, it is just a coding style preference.
Some people prefer if (NULL == ptr) with the argument that if the programmer made a typo (and mistyped the == as a single =) the compiler will complain. However, many compilers would emit a warning for if (ptr=NULL) (at least recent GCC do, when invoked as gcc -Wall -Wextra as you should).
In C++ (where you would use nullptr instead of NULL) there could be a difference, because one can redefine operator ! (e.g. on smart pointers). However, on raw plain pointers (like void*, or sometype* or SomeClass*), you cannot redefine operators like ! or !=.
BTW, some weird processors might have NULL pointers which are not an all zero-bits machine word (but the compiler should deal with this issue). I can't name any such processor in wide use today (however think of 1980s segmented 16 bits x86 as a counter example).
==, too, so it's unclear which is better. Though if you are daft enough to define a==0 != !a, you deserve all that comes to you...0 . There's probably some x86 around today (notably in devices such as cameras and other embedded controllers).NULL always zero.