bsearch(3)

1bsearch(3)                 Library Functions Manual                 bsearch(3)
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NAME

6       bsearch - binary search of a sorted array
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LIBRARY

9       Standard C library (libc, -lc)
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SYNOPSIS

12       #include <stdlib.h>
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14       void *bsearch(const void key[.size], const void base[.size * .nmemb],
15                     size_t nmemb, size_t size,
16                     int (*compar)(const void [.size], const void [.size]));
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DESCRIPTION

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

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

37       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
38       tributes(7).
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40       ┌────────────────────────────────────────────┬───────────────┬─────────┐
41       │Interface                                   │ Attribute     │ Value   │
42       ├────────────────────────────────────────────┼───────────────┼─────────┤
43       │bsearch()                                   │ Thread safety │ MT-Safe │
44       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

47       C11, POSIX.1-2008.
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HISTORY

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

53       The example below first sorts an array of  structures  using  qsort(3),
54       then retrieves desired elements using bsearch().
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56       #include <stdio.h>
57       #include <stdlib.h>
58       #include <string.h>
59
60       #define ARRAY_SIZE(arr)  (sizeof((arr)) / sizeof((arr)[0]))
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62       struct mi {
63           int         nr;
64           const char  *name;
65       };
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67       static struct mi  months[] = {
68           { 1, "jan" }, { 2, "feb" }, { 3, "mar" }, { 4, "apr" },
69           { 5, "may" }, { 6, "jun" }, { 7, "jul" }, { 8, "aug" },
70           { 9, "sep" }, {10, "oct" }, {11, "nov" }, {12, "dec" }
71       };
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73       static int
74       compmi(const void *m1, const void *m2)
75       {
76           const struct mi *mi1 = m1;
77           const struct mi *mi2 = m2;
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79           return strcmp(mi1->name, mi2->name);
80       }
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82       int
83       main(int argc, char *argv[])
84       {
85           qsort(months, ARRAY_SIZE(months), sizeof(months[0]), compmi);
86           for (size_t i = 1; i < argc; i++) {
87               struct mi key;
88               struct mi *res;
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90               key.name = argv[i];
91               res = bsearch(&key, months, ARRAY_SIZE(months),
92                             sizeof(months[0]), compmi);
93               if (res == NULL)
94                   printf("'%s': unknown month\n", argv[i]);
95               else
96                   printf("%s: month #%d\n", res->name, res->nr);
97           }
98           exit(EXIT_SUCCESS);
99       }
100