bsearch(3)

NAME
bsearch - binary search of a sorted array

LIBRARY
Standard C library (libc, -lc)

SYNOPSIS
#include <stdlib.h>

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

DESCRIPTION
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.

RETURN VALUE
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.

ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value
 | Thread safety | MT-Safe

STANDARDS
C11, POSIX.1-2008.

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

EXAMPLES
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>

    #define ARRAY_SIZE(arr)  (sizeof((arr)) / sizeof((arr)[0]))

    struct mi {
        int         nr;
        const char  *name;
    };

    static struct mi  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" }
    };

    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);
    }

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

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

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