Near-Neighbor Searching in Ternary Search Tree

Question

How is the search for the nearest neighbors in the tree? Trying to find information, I get only some formulas without illustrative examples.
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Example of a function:

void nearsearch(Tptr p, char *s, int d) 
{   if (!p || d < 0) return; 
    if (d > 0 || *s < p->splitchar) 
        nearsearch(p->lokid, s, d); 
    if (p->splitchar == 0) { 
       if ((int) strlen(s) <= d) 
          srcharr[srchtop++] = (char *) p->eqkid; 
    } else
       nearsearch(p->eqkid, *s ? s+1:s, 
          (*s == p->splitchar) ? d:d-1); 
    if (d > 0 || *s > p->splitchar) 
        nearsearch(p->hikid, s, d); 
}