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.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" References consulted:
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.\" Linux libc source code
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.\" Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
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.\" 386BSD man pages
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.\" Modified Mon Mar 29 22:41:16 1993, David Metcalfe
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.\" Modified Sat Jul 24 21:35:16 1993, Rik Faith (faith@cs.unc.edu)
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.TH BSEARCH 3 2003-11-01 "" "Linux Programmer's Manual"
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.SH NAME
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bsearch \- binary search of a sorted array
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.SH SYNOPSIS
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.nf
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.B #include <stdlib.h>
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.sp
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.BI "void *bsearch(const void *" key ", const void *" base ", size_t " nmemb ,
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.RS
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.BI "size_t " size ", int (*" compar ")(const void *, const void *));"
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.RE
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.fi
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.SH DESCRIPTION
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The \fBbsearch\fP() function searches an array of \fInmemb\fP objects,
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the initial member of which is pointed to by \fIbase\fP, for a member
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that matches the object pointed to by \fIkey\fP. The size of each member
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of the array is specified by \fIsize\fP.
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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 \fIcompar\fP. The \fIcompar\fP
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routine is expected to have two arguments which point to the \fIkey\fP
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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 \fIkey\fP object is found,
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respectively, to be less than, to match, or be greater than the array
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member.
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.SH "RETURN VALUE"
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The \fBbsearch\fP() function returns a pointer to a matching member of the
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array, or NULL if no match is found. If there are multiple elements that
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match the key, the element returned is unspecified.
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.SH EXAMPLE
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The example below first sorts an array of structures using
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.BR qsort (3),
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then retrieves desired elements using
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.BR bsearch ().
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.sp
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.nf
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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 mi {
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int nr;
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char *name;
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} months[] = {
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{ 1, "jan" }, { 2, "feb" }, { 3, "mar" }, { 4, "apr" },
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{ 5, "may" }, { 6, "jun" }, { 7, "jul" }, { 8, "aug" },
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{ 9, "sep" }, {10, "oct" }, {11, "nov" }, {12, "dec" }
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};
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#define nr_of_months (sizeof(months)/sizeof(months[0]))
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static int compmi(const void *m1, const void *m2) {
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struct mi *mi1 = (struct mi *) m1;
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struct mi *mi2 = (struct mi *) m2;
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return strcmp(mi1\->name, mi2\->name);
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}
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int main(int argc, char **argv) {
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int i;
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qsort(months, nr_of_months, sizeof(struct mi), compmi);
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for (i = 1; i < argc; i++) {
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struct mi key, *res;
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key.name = argv[i];
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res = bsearch(&key, months, nr_of_months,
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sizeof(struct mi), compmi);
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if (res == NULL)
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printf("'%s': unknown month\en", argv[i]);
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else
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printf("%s: month #%d\en", res->name, res->nr);
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}
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return 0;
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}
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.fi
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.\" this example referred to in qsort.3
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.SH "CONFORMING TO"
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SVID 3, 4.3BSD, ISO 9899 (C99)
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.SH "SEE ALSO"
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.BR hsearch (3),
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.BR lsearch (3),
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.BR qsort (3),
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.BR tsearch (3)
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