345e740a1b
Submitted by: fernape MFC after: 1 week Differential revision: https://reviews.freebsd.org/D19902
160 lines
4.5 KiB
Groff
160 lines
4.5 KiB
Groff
.\" Copyright (c) 1990, 1991, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" the American National Standards Committee X3, on Information
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.\" Processing Systems.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)bsearch.3 8.3 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\"
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.Dd July 17, 2019
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.Dt BSEARCH 3
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.Os
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.Sh NAME
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.Nm bsearch
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.Nd binary search of a sorted table
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft void *
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.Fn bsearch "const void *key" "const void *base" "size_t nmemb" "size_t size" "int (*compar) (const void *, const void *)"
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.Sh DESCRIPTION
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The
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.Fn bsearch
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function searches an array of
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.Fa nmemb
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objects, the initial member of which is
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pointed to by
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.Fa base ,
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for a member that matches the object pointed to by
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.Fa key .
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The size of each member of the array is specified by
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.Fa size .
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.Pp
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The contents of the array should be in ascending sorted order according
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to the comparison function referenced by
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.Fa compar .
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The
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.Fa compar
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routine
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is expected to have
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two arguments which point to the
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.Fa key
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object and to an array member, in that order, and should return an integer
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less than, equal to, or greater than zero if the
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.Fa key
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object is found, respectively, to be less than, to match, or be
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greater than the array member.
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See the
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.Fa int_compare
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sample function in
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.Xr qsort 3
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for a comparison function that is also compatible with
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.Fn bsearch .
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.Sh RETURN VALUES
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The
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.Fn bsearch
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function returns a pointer to a matching member of the array, or a null
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pointer if no match is found.
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If two members compare as equal, which member is matched is unspecified.
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.Sh EXAMPLES
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A sample program that searches people by age in a sorted array:
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.Bd -literal
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#include <assert.h>
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#include <stdint.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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struct person {
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const char *name;
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int age;
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};
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static int
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compare(const void *a, const void *b)
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{
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const int *age;
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const struct person *person;
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age = a;
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person = b;
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return (*age - person->age);
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}
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int
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main(void)
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{
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struct person *friend;
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int age;
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/* Sorted array */
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const struct person friends[] = {
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{ "paul", 22 },
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{ "anne", 25 },
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{ "fred", 25 },
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{ "mary", 27 },
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{ "mark", 35 },
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{ "bill", 50 }
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};
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const size_t len = sizeof(friends) / sizeof(friends[0]);
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age = 22;
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friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
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assert(strcmp(friend->name, "paul") == 0);
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printf("name: %s\enage: %d\en", friend->name, friend->age);
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age = 25;
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friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
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/*
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* For multiple elements with the same key, it is implementation
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* defined which will be returned
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*/
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assert(strcmp(friend->name, "fred") == 0 ||
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strcmp(friend->name, "anne") == 0);
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printf("name: %s\enage: %d\en", friend->name, friend->age);
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age = 30;
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friend = bsearch(&age, friends, len, sizeof(friends[0]), compare);
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assert(friend == NULL);
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printf("friend aged 30 not found\en");
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}
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.Ed
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.Sh SEE ALSO
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.Xr db 3 ,
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.Xr lsearch 3 ,
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.Xr qsort 3
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.\" .Xr tsearch 3
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.Sh STANDARDS
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The
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.Fn bsearch
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function conforms to
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.St -isoC .
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