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Message: [QUOTE="Christian Bau, post: 2382391"] How do you do that comparison? Let's say you write char* p = malloc (100); and the call succeeds. "p == NULL" and "p == 0" will both be false. However, it can be true that all the bits in p are zero on this implementation. If you write int i = 0; char* q = (char *) i; then the C99 Standard guarantees that q is a null pointer. On this implementation it means q will point to address 0x12345678 and it will not be equal to p. Unlike most current compilers, a compiler for this implementation will have to produce real code to cast from int to char*. If int and char* have the same size and alignment, then you could try to write * (int *) &q = 0; to set q to a null pointer. This will work on many implementations but not on this one; it is indeed undefined behavior. [/QUOTE]