Copyright (c) 1990 The Regents of the University of California.
All rights reserved.

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@(#)qsort.3 6.4 (Berkeley) 11/26/90

C 4 qsort - quicker sort

#include <stdlib.h>

void
qsort(void *base, size_t nmemb, size_t size,

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int (*compar)(const void *, const void *));

Qsort is a modified partition-exchange sort, or quicksort.

The qsort function sorts an array of nmemb objects, the initial member of which is pointed to by base . The size of each object is specified by size .

The contents of the array are sorted in ascending order according to a comparison function pointed to by compar , which is called with two arguments that point to the objects being compared.

The comparison function must return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

Qsort is not stable, that is, if two members compare as equal, their order in the sorted array is undefined.

Qsort is an implementation of C.A.R. Hoare's ``quicksort'' algorithm, a variant of partition-exchange sorting; in particular, see D.E. Knuth's Algorithm Q. Qsort takes O N lg N average time.

Qsort returns no value. Previous versions of qsort did not permit the comparison routine to itself call qsort (3). This is no longer true. sort(1), radixsort(3) Hoare, C.A.R. [1962]. "Quicksort", The Computer Journal, 5:1, pp. 10-15.

Knuth, D.E. [1968]. "The Art of Computer Programming Vol. 3: Sorting and Searching", pp. 114-123.

Qsort conforms to ANSI X3.159-1989 (``ANSI C'').