tsearch questions

[linbl352]

Does anybody can tell me the following answers?
In the description of tsearch function, what is purpose of the callback function( compar) as follows:
void *tsearch(const void *key, void **rootp,
int(*compar)(const void *, const void *));

also, basicly what are the two parameters in the function (compar)?

[Banfa]

I imagine that the purpose of compar is to compare the 2 values passed to it probably returning

-1 if parameter 1 is less than parameter 2
0 if parameter 1 equals parameter 2
-1 if parameter 1 is greater than parameter 2

This could be used to search within a tree presumably of the key value.