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       bsearch - binary search of a sorted array


       #include <stdlib.h>

       void *bsearch(const void *key, const void *base,
                     size_t nmemb, size_t size,
                     int (*compar)(const void *, const void *));


       The  bsearch() function searches an array of nmemb objects, the initial member of which is
       pointed to by base, for a member that matches the object pointed to by key.  The  size  of
       each member of the array is specified by size.

       The  contents of the array should be in ascending sorted order according to the comparison
       function referenced by compar.  The compar routine is expected to have two arguments which
       point  to  the  key  object  and  to  an array member, in that order, and should return an
       integer less  than,  equal  to,  or  greater  than  zero  if  the  key  object  is  found,
       respectively, to be less than, to match, or be greater than the array member.


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


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue   │
       │bsearch()                                                      │ Thread safety │ MT-Safe │


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


       The  example  below  first  sorts  an  array  of structures using qsort(3), then retrieves
       desired elements using bsearch().

       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>

       struct mi {
           int nr;
           char *name;
       } months[] = {
           { 1, "jan" }, { 2, "feb" }, { 3, "mar" }, { 4, "apr" },
           { 5, "may" }, { 6, "jun" }, { 7, "jul" }, { 8, "aug" },
           { 9, "sep" }, {10, "oct" }, {11, "nov" }, {12, "dec" }

       #define nr_of_months (sizeof(months)/sizeof(months[0]))

       static int
       compmi(const void *m1, const void *m2)
           const struct mi *mi1 = m1;
           const struct mi *mi2 = m2;
           return strcmp(mi1->name, mi2->name);

       main(int argc, char *argv[])
           qsort(months, nr_of_months, sizeof(months[0]), compmi);
           for (int i = 1; i < argc; i++) {
               struct mi key;
               struct mi *res;

      = argv[i];
               res = bsearch(&key, months, nr_of_months,
                             sizeof(months[0]), compmi);
               if (res == NULL)
                   printf("'%s': unknown month\n", argv[i]);
                   printf("%s: month #%d\n", res->name, res->nr);


       hsearch(3), lsearch(3), qsort(3), tsearch(3)


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                                            2021-08-27                                 BSEARCH(3)