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1 | .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk) |
2 | .\" | |
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. | |
6 | .\" | |
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. | |
c13182ef | 11 | .\" |
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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13 | .\" manual page may be incorrect or out-of-date.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 | |
18 | .\" professionally. | |
c13182ef | 19 | .\" |
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20 | .\" Formatted or processed versions of this manual, if unaccompanied by |
21 | .\" the source, must acknowledge the copyright and authors of this work. | |
22 | .\" | |
23 | .\" References consulted: | |
24 | .\" Linux libc source code | |
25 | .\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991) | |
26 | .\" 386BSD man pages | |
27 | .\" | |
28 | .\" Modified 1993-03-29, David Metcalfe | |
29 | .\" Modified 1993-07-24, Rik Faith (faith@cs.unc.edu) | |
788be124 | 30 | .\" 2006-01-15, mtk, Added example program. |
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31 | .\" Modified 2012-03-08, Mark R. Bannister <cambridge@users.sourceforge.net> |
32 | .\" and Ben Bacarisse <software@bsb.me.uk> | |
33 | .\" Document qsort_r() | |
fea681da | 34 | .\" |
6d388dc9 | 35 | .TH QSORT 3 2012-03-08 "" "Linux Programmer's Manual" |
fea681da | 36 | .SH NAME |
b2db77f5 | 37 | qsort, qsort_r \- sort an array |
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38 | .SH SYNOPSIS |
39 | .nf | |
40 | .B #include <stdlib.h> | |
41 | .sp | |
42 | .BI "void qsort(void *" base ", size_t " nmemb ", size_t " size , | |
b2db77f5 | 43 | .BI " int (*" compar ")(const void *, const void *));" |
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44 | .sp |
45 | .BI "void qsort_r(void *" base ", size_t " nmemb ", size_t " size , | |
b2db77f5 | 46 | .BI " int (*" compar ")(const void *, const void *, void *)," |
a094fe6d | 47 | .BI " void *" arg ");" |
fea681da | 48 | .fi |
b2db77f5 BB |
49 | .sp |
50 | .in -4n | |
51 | Feature Test Macro Requirements for glibc (see | |
52 | .BR feature_test_macros (7)): | |
53 | .in | |
54 | .sp | |
55 | .ad l | |
56 | .BR qsort_r (): | |
57 | _GNU_SOURCE | |
58 | .ad b | |
fea681da | 59 | .SH DESCRIPTION |
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60 | The |
61 | .BR qsort () | |
62 | function sorts an array with \fInmemb\fP elements of | |
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63 | size \fIsize\fP. |
64 | The \fIbase\fP argument points to the start of the | |
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65 | array. |
66 | .PP | |
67 | The contents of the array are sorted in ascending order according to a | |
68 | comparison function pointed to by \fIcompar\fP, which is called with two | |
69 | arguments that point to the objects being compared. | |
70 | .PP | |
71 | The comparison function must return an integer less than, equal to, or | |
72 | greater than zero if the first argument is considered to be respectively | |
c13182ef | 73 | less than, equal to, or greater than the second. |
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74 | If two members compare as equal, |
75 | their order in the sorted array is undefined. | |
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76 | .PP |
77 | The | |
78 | .BR qsort_r () | |
79 | function is identical to | |
80 | .BR qsort () | |
81 | except that the comparison function | |
82 | .I compar | |
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83 | takes a third argument. |
84 | A pointer is passed to the comparison function via | |
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85 | .IR arg . |
86 | In this way, the comparison function does not need to use global variables to | |
6d388dc9 | 87 | pass through arbitrary arguments, and is therefore reentrant and safe to |
a094fe6d | 88 | use in threads. |
47297adb | 89 | .SH RETURN VALUE |
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90 | The |
91 | .BR qsort () | |
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92 | and |
93 | .BR qsort_r () | |
94 | functions return no value. | |
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95 | .SH VERSIONS |
96 | .BR qsort_r () | |
97 | was added to glibc in version 2.8. | |
47297adb | 98 | .SH CONFORMING TO |
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99 | The |
100 | .BR qsort () | |
101 | function conforms to SVr4, 4.3BSD, C89, C99. | |
19c98696 | 102 | .SH NOTES |
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103 | Library routines suitable for use as the |
104 | .I compar | |
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105 | argument to |
106 | .BR qsort () | |
107 | include | |
fb186734 | 108 | .BR alphasort (3) |
fea681da | 109 | and |
fb186734 | 110 | .BR versionsort (3). |
c13182ef | 111 | To compare C strings, the comparison function can call |
fb186734 | 112 | .BR strcmp (3), |
cb478668 | 113 | as shown in the example below. |
fea681da | 114 | .SH EXAMPLE |
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115 | For one example of use, see the example under |
116 | .BR bsearch (3). | |
117 | ||
a057d61f | 118 | Another example is the following program, |
48a1cb49 | 119 | which sorts the strings given in its command-line arguments: |
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120 | .sp |
121 | .nf | |
122 | #include <stdio.h> | |
123 | #include <stdlib.h> | |
788be124 | 124 | #include <string.h> |
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125 | |
126 | static int | |
127 | cmpstringp(const void *p1, const void *p2) | |
128 | { | |
7c5bd0eb | 129 | /* The actual arguments to this function are "pointers to |
9daa4fb9 | 130 | pointers to char", but strcmp(3) arguments are "pointers |
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131 | to char", hence the following cast plus dereference */ |
132 | ||
7c5bd0eb | 133 | return strcmp(* (char * const *) p1, * (char * const *) p2); |
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134 | } |
135 | ||
136 | int | |
137 | main(int argc, char *argv[]) | |
138 | { | |
139 | int j; | |
140 | ||
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141 | if (argc < 2) { |
142 | fprintf(stderr, "Usage: %s <string>...\\n", argv[0]); | |
143 | exit(EXIT_FAILURE); | |
144 | } | |
788be124 | 145 | |
29059a65 | 146 | qsort(&argv[1], argc \- 1, sizeof(char *), cmpstringp); |
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147 | |
148 | for (j = 1; j < argc; j++) | |
149 | puts(argv[j]); | |
150 | exit(EXIT_SUCCESS); | |
151 | } | |
152 | .fi | |
47297adb | 153 | .SH SEE ALSO |
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154 | .BR sort (1), |
155 | .BR alphasort (3), | |
156 | .BR strcmp (3), | |
157 | .BR versionsort (3) |