On Wed, Jan 14, 2009 at 13:56, Barry Smith <bsmith at mcs.anl.gov> wrote: > All of this demonstrates that it would be legal that that (!ptr) is not > correct and one should always use if (ptr == NULL).
FWIW, C99, 6.5.3.3.5 reads | The result of the logical negation operator ! is 0 if the value of its operand compares | unequal to 0, 1 if the value of its operand compares equal to 0. The result has type int. | The expression !E is equivalent to (0==E). In (0 == ptr) the 0 is a null pointer constant (as per 6.5.9.2 `one operand is a pointer and the other is a null pointer constant') so there is no reason to prefer (ptr == NULL). Note that in C++, NULL is a macro which expands to 0, not (void*)0 as is common in C, so that it doesn't need an explicit cast. Jed
