A pointer points to the start of its pointee - i.e. the point "just before" its pointee. That's how derived-to-base casts work. That's also how you can have "one-past-the-end" pointers, which are actually "just after" the relevant array.

for example, if you have the following structs

    typedef struct { void *key; } base;
    typedef struct { base b; int misc; int data[2]; } derived;

then derived is laid out as follows

    -----+------+---------+---------+---------+-----
     ... | base | derived | data[0] | data[1] | ...
    -----+------+---------+---------+---------+-----
         ^                ^                   ^
         |                |                   |
        base         derived.data      &derived.data[2]