Re: Questions regarding specialized malloc()/free() replacements

Stephan Beal wrote:
blargg wrote:
[...]
void MyType_init()
[...]
void MyType_free( MyType* p )
{
/* This might be technically non-portable, though portable in
practice */
if ( p != NULL && (void*) p >= blocks &&
(void*) p < blocks += max_blocks )

Why shouldn't this be portable? An array must, by definition, be a
contiguous range of memory, which means that any memory from outside
that range *must* compare not-equal.
[...]

Equal, not equal, sure, but the others require that the pointers be
inside the same object:

| 6.5.8 Relational operators
[...]
| 5 When two pointers are compared, the result depends on the relative
| locations in the address space of the objects pointed to. If two
| pointers to object or incomplete types both point to the same object,
| or both point one past the last element of the same array object, they
| compare equal. If the objects pointed to are members of the same
| aggregate object, pointers to structure members declared later compare
| greater than pointers to members declared earlier in the structure,
| and pointers to array elements with larger subscript values compare
| greater than pointers to elements of the same array with lower
| subscript values. All pointers to members of the same union object
| compare equal. If the expression P points to an element of an array
| object and the expression Q points to the last element of the same
| array object, the pointer expression Q+1 compares greater than P. In
| all other cases, the behavior is undefined.
.

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