These are various C routines for doing a 1-dimensional median search. QuickSelect and Wirth are the fastest for nominal size input data, but require a copy of the array in memory. Torben is much slower for small data, but operates on a read-only data set of arbitrary size (speed difference decreases as data size gets large).
All the functions take the same input parameters and return the same output. The typedef should be changed as appropriate for the input data.