man-pages/man3/bsearch.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Mon Mar 29 22:41:16 1993, David Metcalfe
.\" Modified Sat Jul 24 21:35:16 1993, Rik Faith (faith@cs.unc.edu)
.TH BSEARCH 3  2021-08-27 "" "Linux Programmer's Manual"
.SH NAME
bsearch \- binary search of a sorted array
.SH SYNOPSIS
.nf
.B #include <stdlib.h>
.PP
.BI "void *bsearch(const void *" key ", const void *" base ,
.BI "              size_t " nmemb ", size_t " size ,
.BI "              int (*" compar ")(const void *, const void *));"
.fi
.SH DESCRIPTION
The
.BR bsearch ()
function searches an array of
.I nmemb
objects,
the initial member of which is pointed to by
.IR base ,
for a member
that matches the object pointed to by
.IR key .
The size of each member
of the array is specified by
.IR size .
.PP
The contents of the array should be in ascending sorted order according
to the comparison function referenced by
.IR compar .
The
.I compar
routine is expected to have two arguments which point to the
.I 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
.I key
object is found,
respectively, to be less than, to match, or be greater than the array
member.
.SH RETURN VALUE
The
.BR 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.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.BR bsearch ()
T}	Thread safety	MT-Safe
.TE
.hy
.ad
.sp 1
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
.SH EXAMPLES
The example below first sorts an array of structures using
.BR qsort (3),
then retrieves desired elements using
.BR bsearch ().
.PP
.EX
#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);
}

int
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;

        key.name = argv[i];
        res = bsearch(&key, months, nr_of_months,
                      sizeof(months[0]), compmi);
        if (res == NULL)
            printf("\(aq%s\(aq: unknown month\en", argv[i]);
        else
            printf("%s: month #%d\en", res\->name, res\->nr);
    }
    exit(EXIT_SUCCESS);
}
.EE
.\" this example referred to in qsort.3
.SH SEE ALSO
.BR hsearch (3),
.BR lsearch (3),
.BR qsort (3),
.BR tsearch (3)