cppreference isn't the standard, and while the text they write looks like it's the same verbiage that would be authoritative, it's not. (And there's some criticism of it from standards committee members in that regard).

The current C standard text says:

> The order and contiguity of storage allocated by successive calls to the aligned_alloc, calloc, malloc, and realloc functions is unspecified. The pointer returned if the allocation succeeds is suitably aligned so that it can be assigned to a pointer to any type of object with a fundamental alignment requirement and size less than or equal to the size requested. It can then be used to access such an object or an array of such objects in the space allocated (until the space is explicitly deallocated). The lifetime of an allocated object extends from the allocation until the deallocation. Each such allocation shall yield a pointer to an object disjoint from any other object. The pointer returned points to the start (lowest byte address) of the allocated space. If the space cannot be allocated, a null pointer is returned. If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned to indicate an error, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object.

So yeah, the allocations are required to be unique (at least until it's free'd).

It is in ANSI 89, under memory management functions.