180 lines
6.4 KiB
HTML
180 lines
6.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>lsearch</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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</script>
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<basefont size="3"> <a name="lsearch"></a> <a name="tag_03_353"></a><!-- lsearch -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_353_01"></a>NAME</h4>
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<blockquote>lsearch, lfind - linear search and update</blockquote>
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<h4><a name="tag_03_353_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/search.h.html">search.h</a>><br>
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<br>
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void *lsearch(const void *</tt><i>key</i><tt>, void *</tt><i>base</i><tt>, size_t *</tt><i>nelp</i><tt>, size_t</tt>
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<i>width</i><tt>,<br>
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int (*</tt><i>compar</i><tt>)(const void *, const void *));<br>
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void *lfind(const void *</tt><i>key</i><tt>, const void *</tt><i>base</i><tt>, size_t *</tt><i>nelp</i><tt>,<br>
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size_t width, int (*</tt><i>compar</i><tt>)(const void *, const void *)); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_353_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>lsearch</i>() function shall linearly search the table and return a pointer into the table for the matching entry. If the
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entry does not occur, it shall be added at the end of the table. The <i>key</i> argument points to the entry to be sought in the
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table. The <i>base</i> argument points to the first element in the table. The <i>width</i> argument is the size of an element in
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bytes. The <i>nelp</i> argument points to an integer containing the current number of elements in the table. The integer to which
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<i>nelp</i> points shall be incremented if the entry is added to the table. The <i>compar</i> argument points to a comparison
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function which the application shall supply (for example, <a href="../functions/strcmp.html"><i>strcmp</i>()</a>). It is called
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with two arguments that point to the elements being compared. The application shall ensure that the function returns 0 if the
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elements are equal, and non-zero otherwise.</p>
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<p>The <i>lfind</i>() function shall be equivalent to <i>lsearch</i>(), except that if the entry is not found, it is not added to
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the table. Instead, a null pointer is returned.</p>
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</blockquote>
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<h4><a name="tag_03_353_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If the searched for entry is found, both <i>lsearch</i>() and <i>lfind</i>() shall return a pointer to it. Otherwise,
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<i>lfind</i>() shall return a null pointer and <i>lsearch</i>() shall return a pointer to the newly added element.</p>
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<p>Both functions shall return a null pointer in case of error.</p>
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</blockquote>
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<h4><a name="tag_03_353_05"></a>ERRORS</h4>
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<blockquote>
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<p>No errors are defined.</p>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_353_06"></a>EXAMPLES</h4>
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<blockquote>
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<h5><a name="tag_03_353_06_01"></a>Storing Strings in a Table</h5>
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<p>This fragment reads in less than or equal to TABSIZE strings of length less than or equal to ELSIZE and stores them in a table,
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eliminating duplicates.</p>
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<pre>
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<tt>#include <stdio.h>
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#include <string.h>
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#include <search.h>
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<br>
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#define TABSIZE 50
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#define ELSIZE 120
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<br>
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...
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char line[ELSIZE], tab[TABSIZE][ELSIZE];
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size_t nel = 0;
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...
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while (fgets(line, ELSIZE, stdin) != NULL && nel < TABSIZE)
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(void) lsearch(line, tab, &nel,
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ELSIZE, (int (*)(const void *, const void *)) strcmp);
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...
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</tt>
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</pre>
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<h5><a name="tag_03_353_06_02"></a>Finding a Matching Entry</h5>
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<p>The following example finds any line that reads <tt>"This is a test."</tt> .</p>
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<pre>
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<tt>#include <search.h>
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#include <string.h>
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...
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char line[ELSIZE], tab[TABSIZE][ELSIZE];
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size_t nel = 0;
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char *findline;
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void *entry;
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<br>
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findline = "This is a test.\n";
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<br>
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entry = lfind(findline, tab, &nel, ELSIZE, (
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int (*)(const void *, const void *)) strcmp);
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_353_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The comparison function need not compare every byte, so arbitrary data may be contained in the elements in addition to the
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values being compared.</p>
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<p>Undefined results can occur if there is not enough room in the table to add a new item.</p>
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</blockquote>
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<h4><a name="tag_03_353_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_353_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_353_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="hcreate.html"><i>hcreate</i>()</a> , <a href="tsearch.html"><i>tsearch</i>()</a> , the Base Definitions volume of
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IEEE Std 1003.1-2001, <a href="../basedefs/search.h.html"><i><search.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_353_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 1. Derived from Issue 1 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_353_12"></a>Issue 6</h4>
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<blockquote>
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<p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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