bsearch(3)

1BSEARCH(3)                 Linux Programmer's Manual                BSEARCH(3)
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NAME

6       bsearch - binary search of a sorted array
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SYNOPSIS

9       #include <stdlib.h>
10
11       void *bsearch(const void *key, const void *base,
12                     size_t nmemb, size_t size,
13                     int (*compar)(const void *, const void *));
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DESCRIPTION

16       The  bsearch() function searches an array of nmemb objects, the initial
17       member of which is pointed to by base, for a member  that  matches  the
18       object  pointed  to  by  key.   The size of each member of the array is
19       specified by size.
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21       The contents of the array should be in ascending sorted order according
22       to the comparison function referenced by compar.  The compar routine is
23       expected to have two arguments which point to the key object and to  an
24       array  member,  in  that order, and should return an integer less than,
25       equal to, or greater than zero if the  key  object  is  found,  respec‐
26       tively, to be less than, to match, or be greater than the array member.
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RETURN VALUE

29       The  bsearch()  function  returns a pointer to a matching member of the
30       array, or NULL if no match is found.  If there  are  multiple  elements
31       that match the key, the element returned is unspecified.
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ATTRIBUTES

34       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
35       tributes(7).
36
37       ┌────────────────────────────────────────────┬───────────────┬─────────┐
38       │Interface                                   │ Attribute     │ Value   │
39       ├────────────────────────────────────────────┼───────────────┼─────────┤
40       │bsearch()                                   │ Thread safety │ MT-Safe │
41       └────────────────────────────────────────────┴───────────────┴─────────┘
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CONFORMING TO

44       POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
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EXAMPLES

47       The example below first sorts an array of  structures  using  qsort(3),
48       then retrieves desired elements using bsearch().
49
50       #include <stdio.h>
51       #include <stdlib.h>
52       #include <string.h>
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54       struct mi {
55           int nr;
56           char *name;
57       } months[] = {
58           { 1, "jan" }, { 2, "feb" }, { 3, "mar" }, { 4, "apr" },
59           { 5, "may" }, { 6, "jun" }, { 7, "jul" }, { 8, "aug" },
60           { 9, "sep" }, {10, "oct" }, {11, "nov" }, {12, "dec" }
61       };
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63       #define nr_of_months (sizeof(months)/sizeof(months[0]))
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65       static int
66       compmi(const void *m1, const void *m2)
67       {
68           const struct mi *mi1 = m1;
69           const struct mi *mi2 = m2;
70           return strcmp(mi1->name, mi2->name);
71       }
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73       int
74       main(int argc, char **argv)
75       {
76           qsort(months, nr_of_months, sizeof(months[0]), compmi);
77           for (int i = 1; i < argc; i++) {
78               struct mi key;
79               struct mi *res;
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81               key.name = argv[i];
82               res = bsearch(&key, months, nr_of_months,
83                             sizeof(months[0]), compmi);
84               if (res == NULL)
85                   printf("'%s': unknown month\n", argv[i]);
86               else
87                   printf("%s: month #%d\n", res->name, res->nr);
88           }
89           exit(EXIT_SUCCESS);
90       }
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COLOPHON

96       This  page  is  part of release 5.12 of the Linux man-pages project.  A
97       description of the project, information about reporting bugs,  and  the
98       latest     version     of     this    page,    can    be    found    at
99       https://www.kernel.org/doc/man-pages/.
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103                                  2021-03-22                        BSEARCH(3)