arielby

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

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