.\" Copyright (c) 1990, 1991, 1993 .\" The Regents of the University of California. 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. .\" 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 8.1 (Berkeley) 6/4/93 .\" $FreeBSD: src/lib/libc/stdlib/qsort.3,v 1.17 2007/01/09 00:28:10 imp Exp $ .\" .Dd September 30, 2003 .Dt QSORT 3 .Os .Sh NAME .Nm heapsort , #ifdef UNIFDEF_BLOCKS .Nm heapsort_b , #endif .Nm mergesort , #ifdef UNIFDEF_BLOCKS .Nm mergesort_b , #endif .Nm qsort , #ifdef UNIFDEF_BLOCKS .Nm qsort_b , #endif .Nm qsort_r .Nd sort functions .Sh SYNOPSIS .In stdlib.h .Ft int .Fo heapsort .Fa "void *base" .Fa "size_t nel" .Fa "size_t width" .Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]" .Fc #ifdef UNIFDEF_BLOCKS .Ft int .Fo heapsort_b .Fa "void *base" .Fa "size_t nel" .Fa "size_t width" .Fa "int \*[lp]^compar\*[rp]\*[lp]const void *, const void *\*[rp]" .Fc #endif .Ft int .Fo mergesort .Fa "void *base" .Fa "size_t nel" .Fa "size_t width" .Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]" .Fc #ifdef UNIFDEF_BLOCKS .Ft int .Fo mergesort_b .Fa "void *base" .Fa "size_t nel" .Fa "size_t width" .Fa "int \*[lp]^compar\*[rp]\*[lp]const void *, const void *\*[rp]" .Fc #endif .Ft void .Fo qsort .Fa "void *base" .Fa "size_t nel" .Fa "size_t width" .Fa "int \*[lp]*compar\*[rp]\*[lp]const void *, const void *\*[rp]" .Fc #ifdef UNIFDEF_BLOCKS .Ft void .Fo qsort_b .Fa "void *base" .Fa "size_t nel" .Fa "size_t width" .Fa "int \*[lp]^compar\*[rp]\*[lp]const void *, const void *\*[rp]" .Fc #endif .Ft void .Fo qsort_r .Fa "void *base" .Fa "size_t nel" .Fa "size_t width" .Fa "void *thunk" .Fa "int \*[lp]*compar\*[rp]\*[lp]void *, const void *, const void *\*[rp]" .Fc .Sh DESCRIPTION The .Fn qsort function is a modified partition-exchange sort, or quicksort. The .Fn heapsort function is a modified selection sort. The .Fn mergesort function is a modified merge sort with exponential search, intended for sorting data with pre-existing order. .Pp The .Fn qsort and .Fn heapsort functions sort an array of .Fa nel objects, the initial member of which is pointed to by .Fa base . The size of each object is specified by .Fa width . The .Fn mergesort function behaves similarly, but .Em requires that .Fa width be greater than or equal to .Dq "sizeof(void *) / 2" . .Pp The contents of the array .Fa base are sorted in ascending order according to a comparison function pointed to by .Fa compar , which requires two arguments pointing to the objects being compared. .Pp 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. .Pp The .Fn qsort_r function behaves identically to .Fn qsort , except that it takes an additional argument, .Fa thunk , which is passed unchanged as the first argument to function pointed to .Fa compar . This allows the comparison function to access additional data without using global variables, and thus .Fn qsort_r is suitable for use in functions which must be reentrant. .Pp The algorithms implemented by .Fn qsort , .Fn qsort_r , and .Fn heapsort are .Em not stable; that is, if two members compare as equal, their order in the sorted array is undefined. The .Fn mergesort algorithm is stable. .Pp The .Fn qsort and .Fn qsort_r functions are an implementation of C.A.R. Hoare's .Dq quicksort algorithm, a variant of partition-exchange sorting; in particular, see .An D.E. Knuth Ns 's .%T "Algorithm Q" . .Sy Quicksort takes O N lg N average time. This implementation uses median selection to avoid its O N**2 worst-case behavior. .Pp The .Fn heapsort function is an implementation of .An "J.W.J. William" Ns 's .Dq heapsort algorithm, a variant of selection sorting; in particular, see .An "D.E. Knuth" Ns 's .%T "Algorithm H" . .Sy Heapsort takes O N lg N worst-case time. Its .Em only advantage over .Fn qsort is that it uses almost no additional memory; while .Fn qsort does not allocate memory, it is implemented using recursion. .Pp The function .Fn mergesort requires additional memory of size .Fa nel * .Fa width bytes; it should be used only when space is not at a premium. The .Fn mergesort function is optimized for data with pre-existing order; its worst case time is O N lg N; its best case is O N. .Pp Normally, .Fn qsort is faster than .Fn mergesort which is faster than .Fn heapsort . Memory availability and pre-existing order in the data can make this untrue. #ifdef UNIFDEF_BLOCKS .Pp The .Fn heapsort_b , .Fn mergesort_b , and .Fn qsort_b routines are like the corresponding routines without the _b suffix, expect that the .Fa compar callback is a block pointer instead of a function pointer. #endif .Sh RETURN VALUES The #ifdef UNIFDEF_BLOCKS .Fn qsort , .Fn qsort_b #else .Fn qsort #endif and .Fn qsort_r functions return no value. .Pp #ifdef UNIFDEF_BLOCKS .ds HEAPSORT_B heapsort_b .ds MERGESORT_B mergesort_b #endif .Rv -std heapsort \*[HEAPSORT_B] mergesort \*[MERGESORT_B] .Sh COMPATIBILITY Previous versions of .Fn qsort did not permit the comparison routine itself to call .Fn qsort 3 . This is no longer true. .Sh ERRORS The #ifdef UNIFDEF_BLOCKS .Fn heapsort , .Fn heapsort_b , .Fn mergesort , and .Fn mergesort_b #else .Fn heapsort and .Fn mergesort #endif functions succeed unless: .Bl -tag -width Er .It Bq Er EINVAL The .Fa width argument is zero, or, the .Fa width argument to .Fn mergesort #ifdef UNIFDEF_BLOCKS or .Fn mergesort_b #endif is less than .Dq "sizeof(void *) / 2" . .It Bq Er ENOMEM The #ifdef UNIFDEF_BLOCKS .Fn heapsort , .Fn heapsort_b , .Fn mergesort , or .Fn mergesort_b #else .Fn heapsort or .Fn mergesort #endif functions were unable to allocate memory. .El .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 .Rs .%A McIlroy, P.M. .%T "Optimistic Sorting and Information Theoretic Complexity" .%J "Fourth Annual ACM-SIAM Symposium on Discrete Algorithms" .%V January 1992 .Re .Rs .%A Bentley, J.L. .%A McIlroy, M.D. .%T "Engineering a Sort Function" .%J "Software--Practice and Experience" .%V Vol. 23(11) .%P pp. 1249-1265 .%D November\ 1993 .Re .Sh STANDARDS The .Fn qsort function conforms to .St -isoC .