Re: [Gretl-devel] msortby() stumbles over NA / nan

On Thu, 4 Dec 2014, Sven Schreiber wrote:

>> >> I tried a little test program on Windows 8. It turns out that the C >> library does return 0 for all comparisons involving a NaN (>, < and >> ==), as it should. Nonetheless, qsort() with our original simple >> callback sorts NaN (invoked via 0.0/0.0) to the start of an array of >> doubles. I don't know how that happens! > > sorry for being clueless, but what is qsort() -- gretl's internal call > to a quicksort algorithm perhaps? qsort is the standard C library quicksort function (defined in stdlib.h). Gretl calls it for sorting -- we haven't felt a need for our own quicksort implementation. But to use qsort you need to supply your own comparison function for the objects you're sorting (what I'm calling the "callback").