Is NULL always false?

Question

Is it safe to assume that NULL always translates to false in C?

void *somePtr = NULL;

if (!somePtr) {
  /* This will always be executed? */
}

Or should an explicit check against the value of NULL be made?

Answer 1

Yes. NULL evaluates to false, since C considers any non-zero value true and any zero value false. NULL is essentially the zero address and is treated as such in comparisons, and I believe would be promoted to an int for the boolean check. I would expect that your code is readable to anyone familiar with C although I would probably make the check explicit.

In C and C++ programming, two null pointers are guaranteed to compare equal; ANSI C guarantees that any null pointer will be equal to 0 in a comparison with an integer type; furthermore the macro NULL is defined as a null pointer constant, that is value 0 (either as an integer type or converted to a pointer to void), so a null pointer will compare equal to NULL.

Ref: http://en.wikipedia.org/wiki/Null_pointer#Null_pointer