man3/bsearch.3

   1 .\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
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  23 .\" References consulted:
  24 .\"     Linux libc source code
  25 .\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
  26 .\"     386BSD man pages
  27 .\" Modified Mon Mar 29 22:41:16 1993, David Metcalfe
  28 .\" Modified Sat Jul 24 21:35:16 1993, Rik Faith (faith@cs.unc.edu)
  29 .TH BSEARCH 3  2003-11-01 "" "Linux Programmer's Manual"
  30 .SH NAME
  31 bsearch \- binary search of a sorted array
  32 .SH SYNOPSIS
  33 .nf
  34 .B #include <stdlib.h>
  35 .sp
  36 .BI "void *bsearch(const void *" key ", const void *" base ,
  37 .BI "              size_t " nmemb ", size_t " size ,
  38 .BI "              int (*" compar ")(const void *, const void *));"
  39 .fi
  40 .SH DESCRIPTION
  41 The
  42 .BR bsearch ()
  43 function searches an array of \fInmemb\fP objects,
  44 the initial member of which is pointed to by \fIbase\fP, for a member
  45 that matches the object pointed to by \fIkey\fP.
  46 The size of each member
  47 of the array is specified by \fIsize\fP.
  48 .PP
  49 The contents of the array should be in ascending sorted order according
  50 to the comparison function referenced by \fIcompar\fP.
  51 The \fIcompar\fP
  52 routine is expected to have two arguments which point to the \fIkey\fP
  53 object and to an array member, in that order, and should return an integer
  54 less than, equal to, or greater than zero if the \fIkey\fP object is found,
  55 respectively, to be less than, to match, or be greater than the array
  56 member.
  57 .SH "RETURN VALUE"
  58 The
  59 .BR bsearch ()
  60 function returns a pointer to a matching member of the
  61 array, or NULL if no match is found.
  62 If there are multiple elements that
  63 match the key, the element returned is unspecified.
  64 .SH "CONFORMING TO"
  65 SVr4, 4.3BSD, POSIX.1-2001, C89, C99.
  66 .SH EXAMPLE
  67 The example below first sorts an array of structures using
  68 .BR qsort (3),
  69 then retrieves desired elements using
  70 .BR bsearch ().
  71 .sp
  72 .nf
  73 #include <stdio.h>
  74 #include <stdlib.h>
  75 #include <string.h>
  76
  77 struct mi {
  78     int nr;
  79     char *name;
  80 } months[] = {
  81     { 1, "jan" }, { 2, "feb" }, { 3, "mar" }, { 4, "apr" },
  82     { 5, "may" }, { 6, "jun" }, { 7, "jul" }, { 8, "aug" },
  83     { 9, "sep" }, {10, "oct" }, {11, "nov" }, {12, "dec" }
  84 };
  85
  86 #define nr_of_months (sizeof(months)/sizeof(months[0]))
  87
  88 static int
  89 compmi(const void *m1, const void *m2)
  90 {
  91     struct mi *mi1 = (struct mi *) m1;
  92     struct mi *mi2 = (struct mi *) m2;
  93     return strcmp(mi1\->name, mi2\->name);
  94 }
  95
  96 int
  97 main(int argc, char **argv)
  98 {
  99     int i;
 100
 101     qsort(months, nr_of_months, sizeof(struct mi), compmi);
 102     for (i = 1; i < argc; i++) {
 103         struct mi key, *res;
 104         key.name = argv[i];
 105         res = bsearch(&key, months, nr_of_months,
 106                       sizeof(struct mi), compmi);
 107         if (res == NULL)
 108             printf("\(aq%s\(aq: unknown month\en", argv[i]);
 109         else
 110             printf("%s: month #%d\en", res\->name, res\->nr);
 111     }
 112     exit(EXIT_SUCCESS);
 113 }
 114 .fi
 115 .\" this example referred to in qsort.3
 116 .SH "SEE ALSO"
 117 .BR hsearch (3),
 118 .BR lsearch (3),
 119 .BR qsort (3),
 120 .BR tsearch (3)