All rights reserved.
This code is derived from software contributed to Berkeley by
the American National Standards Committee X3, on Information
Processing Systems.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in the
documentation and/or other materials provided with the distribution.
3. All advertising materials mentioning features or use of this software
must display the following acknowledgement:
This product includes software developed by the University of
California, Berkeley and its contributors.
4. Neither the name of the University nor the names of its contributors
may be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
@(#)qsort.3 6.7 (Berkeley) 6/29/91
.Dd June 29, 1991 .Dt QSORT 3 .Os .Sh NAME .Nm qsort, heapsort .Nd sort functions .Sh SYNOPSIS .Fd #include <stdlib.h> .Ft void .Fn qsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)" .Ft int .Fn heapsort "void *base" "size_t nmemb" "size_t size" "int (*compar)(const void *, const void *)" .Sh DESCRIPTION The .Fn qsort function is a modified partition-exchange sort, or quicksort. The .Fn heapsort function is a modified selection sort.
p The .Fn qsort and .Fn heapsort functions sort an array of .Fa nmemb objects, the initial member of which is pointed to by .Fa base . The size of each object is specified by .Fa size .
p The contents of the array are sorted in ascending order according to a comparison function pointed to by .Fa compar , which is called with two arguments that point to the objects being compared.
p 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.
p The functions .Fn qsort and .Fn heapsort are .Em not stable, that is, if two members compare as equal, their order in the sorted array is undefined.
p The .Fn qsort function 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. .Fn Qsort takes O N lg N average time. This implementation uses median selection to avoid the traditional O N**2 worst-case behavior.
p The .Fn heapsort function is an implementation of J.W.J. William's ``heapsort'' algorithm, a variant of selection sorting; in particular, see D.E. Knuth's Algorithm H. .Fn Heapsort takes O N lg N worst-case time. Its .Em only advantage over .Fn qsort is that it uses no additional memory. .Sh RETURN VALUES The .Fn qsort function returns no value.
p Upon successful completion, .Fn heapsort returns 0. Otherwise, it returns -1 and the global variable .Va errno is set to indicate the error. .Sh ERRORS The .Fn heapsort function succeeds unless: l -tag -width Er t Bq Er EINVAL The .Fa size argument is zero. .Sh COMPATIBILITY Previous versions of .Fn qsort did not permit the comparison routine to itself call .Fn qsort 3 . This is no longer true. .Sh SEE ALSO .Xr sort 1 , .Xr radixsort 3 .Rs .%A Hoare, C.A.R. .%D 1962 .%T "Quicksort" .%J "The Computer Journal" .%V 5:1 .%P pp. 10-15 .Re .Rs .%A Williams, J.W.J .%D 1964 .%T "Heapsort" .%J "Communications of the ACM" .%V 7:1 .%P pp. 347-348 .Re .Rs .%A Knuth, D.E. .%D 1968 .%B "The Art of Computer Programming" .%V Vol. 3 .%T "Sorting and Searching" .%P pp. 114-123, 145-149 .Re .Sh STANDARDS The .Fn qsort function conforms to .St -ansiC .
Indexes created Sun Oct 05 05:09:57 GMT 2025