1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" Permission is granted to make and distribute verbatim copies of this
4 .\" manual provided the copyright notice and this permission notice are
5 .\" preserved on all copies.
7 .\" Permission is granted to copy and distribute modified versions of this
8 .\" manual under the conditions for verbatim copying, provided that the
9 .\" entire resulting derived work is distributed under the terms of a
10 .\" permission notice identical to this one.
12 .\" Since the Linux kernel and libraries are constantly changing, this
13 .\" manual page may be incorrect or out-of-date. The author(s) assume no
14 .\" responsibility for errors or omissions, or for damages resulting from
15 .\" the use of the information contained herein. The author(s) may not
16 .\" have taken the same level of care in the production of this manual,
17 .\" which is licensed free of charge, as they might when working
20 .\" Formatted or processed versions of this manual, if unaccompanied by
21 .\" the source, must acknowledge the copyright and authors of this work.
23 .\" References consulted:
24 .\" Linux libc source code
25 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
28 .\" Modified 1993-03-29, David Metcalfe
29 .\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
30 .\" 2006-01-15, mtk, Added example program.
32 .\" FIXME glibc 2.8 added qsort_r(), which needs to be documented.
34 .TH QSORT 3 2009-09-15 "" "Linux Programmer's Manual"
36 qsort \- sorts an array
39 .B #include <stdlib.h>
41 .BI "void qsort(void *" base ", size_t " nmemb ", size_t " size ,
42 .BI " int(*" compar ")(const void *, const void *));"
47 function sorts an array with \fInmemb\fP elements of
49 The \fIbase\fP argument points to the start of the
52 The contents of the array are sorted in ascending order according to a
53 comparison function pointed to by \fIcompar\fP, which is called with two
54 arguments that point to the objects being compared.
56 The comparison function must return an integer less than, equal to, or
57 greater than zero if the first argument is considered to be respectively
58 less than, equal to, or greater than the second.
59 If two members compare
60 as equal, their order in the sorted array is undefined.
64 function returns no value.
66 SVr4, 4.3BSD, C89, C99.
68 Library routines suitable for use as the
74 To compare C strings, the comparison function can call
76 as shown in the example below.
78 For one example of use, see the example under
81 Another example is the following program,
82 which sorts the strings given in its command-line arguments:
90 cmpstringp(const void *p1, const void *p2)
92 /* The actual arguments to this function are "pointers to
93 pointers to char", but strcmp(3) arguments are "pointers
94 to char", hence the following cast plus dereference */
96 return strcmp(* (char * const *) p1, * (char * const *) p2);
100 main(int argc, char *argv[])
105 fprintf(stderr, "Usage: %s <string>...\\n", argv[0]);
109 qsort(&argv[1], argc \- 1, sizeof(char *), cmpstringp);
111 for (j = 1; j < argc; j++)