KITFORMA · EDITORIAL ANSWER
Why can returning a-b from a qsort comparator misorder integers?
KitForma editorial guide. Subtracting two arbitrary signed integers can overflow, and the comparator then fails to represent a consistent ordering. Extreme values expose errors that ordinary positive samples conceal.
Step-by-step answer
Subtracting two arbitrary signed integers can overflow, and the comparator then fails to represent a consistent ordering. Extreme values expose errors that ordinary positive samples conceal.
Read the values with correctly typed pointers and return
(a > b) - (a < b) for ascending integer order. Keep the comparator free of state changes and ensure its ordering remains consistent for all compared pairs. Use additional fields explicitly for tie-breaking.
Test minimum, maximum, zero and repeated values, checking both order and element preservation. qsort is not required to preserve input order among equal elements; include an original-position tie-breaker when stable presentation is part of the requirement.Sources and verification
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