1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
3 .\" %%%LICENSE_START(VERBATIM)
4 .\" Permission is granted to make and distribute verbatim copies of this
5 .\" manual provided the copyright notice and this permission notice are
6 .\" preserved on all copies.
8 .\" Permission is granted to copy and distribute modified versions of this
9 .\" manual under the conditions for verbatim copying, provided that the
10 .\" entire resulting derived work is distributed under the terms of a
11 .\" permission notice identical to this one.
13 .\" Since the Linux kernel and libraries are constantly changing, this
14 .\" manual page may be incorrect or out-of-date. The author(s) assume no
15 .\" responsibility for errors or omissions, or for damages resulting from
16 .\" the use of the information contained herein. The author(s) may not
17 .\" have taken the same level of care in the production of this manual,
18 .\" which is licensed free of charge, as they might when working
21 .\" Formatted or processed versions of this manual, if unaccompanied by
22 .\" the source, must acknowledge the copyright and authors of this work.
25 .\" References consulted:
26 .\" Linux libc source code
27 .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
30 .\" Modified 1993-03-29, David Metcalfe
31 .\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu)
32 .\" 2006-01-15, mtk, Added example program.
33 .\" Modified 2012-03-08, Mark R. Bannister <cambridge@users.sourceforge.net>
34 .\" and Ben Bacarisse <software@bsb.me.uk>
35 .\" Document qsort_r()
37 .TH QSORT 3 2012-03-08 "" "Linux Programmer's Manual"
39 qsort, qsort_r \- sort an array
42 .B #include <stdlib.h>
44 .BI "void qsort(void *" base ", size_t " nmemb ", size_t " size ,
45 .BI " int (*" compar ")(const void *, const void *));"
47 .BI "void qsort_r(void *" base ", size_t " nmemb ", size_t " size ,
48 .BI " int (*" compar ")(const void *, const void *, void *),"
49 .BI " void *" arg ");"
53 Feature Test Macro Requirements for glibc (see
54 .BR feature_test_macros (7)):
64 function sorts an array with \fInmemb\fP elements of
66 The \fIbase\fP argument points to the start of the
69 The contents of the array are sorted in ascending order according to a
70 comparison function pointed to by \fIcompar\fP, which is called with two
71 arguments that point to the objects being compared.
73 The comparison function must return an integer less than, equal to, or
74 greater than zero if the first argument is considered to be respectively
75 less than, equal to, or greater than the second.
76 If two members compare as equal,
77 their order in the sorted array is undefined.
81 function is identical to
83 except that the comparison function
85 takes a third argument.
86 A pointer is passed to the comparison function via
88 In this way, the comparison function does not need to use global variables to
89 pass through arbitrary arguments, and is therefore reentrant and safe to
96 functions return no value.
99 was added to glibc in version 2.8.
103 function conforms to SVr4, 4.3BSD, C89, C99.
105 Library routines suitable for use as the
113 To compare C strings, the comparison function can call
115 as shown in the example below.
117 For one example of use, see the example under
120 Another example is the following program,
121 which sorts the strings given in its command-line arguments:
129 cmpstringp(const void *p1, const void *p2)
131 /* The actual arguments to this function are "pointers to
132 pointers to char", but strcmp(3) arguments are "pointers
133 to char", hence the following cast plus dereference */
135 return strcmp(* (char * const *) p1, * (char * const *) p2);
139 main(int argc, char *argv[])
144 fprintf(stderr, "Usage: %s <string>...\\n", argv[0]);
148 qsort(&argv[1], argc \- 1, sizeof(char *), cmpstringp);
150 for (j = 1; j < argc; j++)