📄 hsearch.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html><head><meta name="generator" content="HTML Tidy, see www.w3.org"><meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 --><!-- Copyright (c) 2001-2003 The Open Group, All Rights Reserved --><title>hcreate</title></head><body bgcolor="white"><script type="text/javascript" language="JavaScript" src="../jscript/codes.js"></script><basefont size="3"> <a name="hcreate"></a> <a name="tag_03_264"></a><!-- hcreate --> <!--header start--><center><font size="2">The Open Group Base Specifications Issue 6<br>IEEE Std 1003.1, 2003 Edition<br>Copyright © 2001-2003 The IEEE and The Open Group, All Rights reserved.</font></center><!--header end--><hr size="2" noshade><h4><a name="tag_03_264_01"></a>NAME</h4><blockquote>hcreate, hdestroy, hsearch - manage hash search table</blockquote><h4><a name="tag_03_264_02"></a>SYNOPSIS</h4><blockquote class="synopsis"><div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt="[Option Start]" border="0"> #include <<a href="../basedefs/search.h.html">search.h</a>><br><br> int hcreate(size_t</tt> <i>nel</i><tt>);<br> void hdestroy(void);<br> ENTRY *hsearch(ENTRY</tt> <i>item</i><tt>, ACTION</tt> <i>action</i><tt>); <img src="../images/opt-end.gif" alt="[Option End]"border="0"></tt></code></div><tt><br></tt></blockquote><h4><a name="tag_03_264_03"></a>DESCRIPTION</h4><blockquote><p>The <i>hcreate</i>(), <i>hdestroy</i>(), and <i>hsearch</i>() functions shall manage hash search tables.</p><p>The <i>hcreate</i>() function shall allocate sufficient space for the table, and the application shall ensure it is calledbefore <i>hsearch</i>() is used. The <i>nel</i> argument is an estimate of the maximum number of entries that the table shallcontain. This number may be adjusted upward by the algorithm in order to obtain certain mathematically favorable circumstances.</p><p>The <i>hdestroy</i>() function shall dispose of the search table, and may be followed by another call to <i>hcreate</i>(). Afterthe call to <i>hdestroy</i>(), the data can no longer be considered accessible.</p><p>The <i>hsearch</i>() function is a hash-table search routine. It shall return a pointer into a hash table indicating thelocation at which an entry can be found. The <i>item</i> argument is a structure of type <b>ENTRY</b> (defined in the <a href="../basedefs/search.h.html"><i><search.h></i></a> header) containing two pointers: <i>item.key</i> points to the comparisonkey (a <b>char *</b>), and <i>item.data</i> (a <b>void *</b>) points to any other data to be associated with that key. Thecomparison function used by <i>hsearch</i>() is <a href="../functions/strcmp.html"><i>strcmp</i>()</a>. The <i>action</i> argumentis a member of an enumeration type <b>ACTION</b> indicating the disposition of the entry if it cannot be found in the table. ENTERindicates that the item should be inserted in the table at an appropriate point. FIND indicates that no entry should be made.Unsuccessful resolution is indicated by the return of a null pointer.</p><p>These functions need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe.</p></blockquote><h4><a name="tag_03_264_04"></a>RETURN VALUE</h4><blockquote><p>The <i>hcreate</i>() function shall return 0 if it cannot allocate sufficient space for the table; otherwise, it shall returnnon-zero.</p><p>The <i>hdestroy</i>() function shall not return a value.</p><p>The <i>hsearch</i>() function shall return a null pointer if either the action is FIND and the item could not be found or theaction is ENTER and the table is full.</p></blockquote><h4><a name="tag_03_264_05"></a>ERRORS</h4><blockquote><p>The <i>hcreate</i>() and <i>hsearch</i>() functions may fail if:</p><dl compact><dt>[ENOMEM]</dt><dd>Insufficient storage space is available.</dd></dl></blockquote><hr><div class="box"><em>The following sections are informative.</em></div><h4><a name="tag_03_264_06"></a>EXAMPLES</h4><blockquote><p>The following example reads in strings followed by two numbers and stores them in a hash table, discarding duplicates. It thenreads in strings and finds the matching entry in the hash table and prints it out.</p><pre><tt>#include <stdio.h>#include <search.h>#include <string.h><br>struct info { /* This is the info stored in the table */ int age, room; /* other than the key. */};<br>#define NUM_EMPL 5000 /* # of elements in search table. */<br>int main(void){ char string_space[NUM_EMPL*20]; /* Space to store strings. */ struct info info_space[NUM_EMPL]; /* Space to store employee info. */ char *str_ptr = string_space; /* Next space in string_space. */ struct info *info_ptr = info_space; /* Next space in info_space. */ ENTRY item; ENTRY *found_item; /* Name to look for in table. */ char name_to_find[30];<br> int i = 0;<br> /* Create table; no error checking is performed. */ (void) hcreate(NUM_EMPL); while (scanf("%s%d%d", str_ptr, &info_ptr->age, &info_ptr->room) != EOF && i++ < NUM_EMPL) {<br> /* Put information in structure, and structure in item. */ item.key = str_ptr; item.data = info_ptr; str_ptr += strlen(str_ptr) + 1; info_ptr++;<br> /* Put item into table. */ (void) hsearch(item, ENTER); }<br> /* Access table. */ item.key = name_to_find; while (scanf("%s", item.key) != EOF) { if ((found_item = hsearch(item, FIND)) != NULL) {<br> /* If item is in the table. */ (void)printf("found %s, age = %d, room = %d\n", found_item->key, ((struct info *)found_item->data)->age, ((struct info *)found_item->data)->room); } else (void)printf("no such employee %s\n", name_to_find); } return 0;}</tt></pre></blockquote><h4><a name="tag_03_264_07"></a>APPLICATION USAGE</h4><blockquote><p>The <i>hcreate</i>() and <i>hsearch</i>() functions may use <a href="../functions/malloc.html"><i>malloc</i>()</a> to allocatespace.</p></blockquote><h4><a name="tag_03_264_08"></a>RATIONALE</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_264_09"></a>FUTURE DIRECTIONS</h4><blockquote><p>None.</p></blockquote><h4><a name="tag_03_264_10"></a>SEE ALSO</h4><blockquote><p><a href="bsearch.html"><i>bsearch</i>()</a> , <a href="lsearch.html"><i>lsearch</i>()</a> , <a href="malloc.html"><i>malloc</i>()</a> , <a href="strcmp.html"><i>strcmp</i>()</a> , <a href="tsearch.html"><i>tsearch</i>()</a> , theBase Definitions volume of IEEE Std 1003.1-2001, <a href="../basedefs/search.h.html"><i><search.h></i></a></p></blockquote><h4><a name="tag_03_264_11"></a>CHANGE HISTORY</h4><blockquote><p>First released in Issue 1. Derived from Issue 1 of the SVID.</p></blockquote><h4><a name="tag_03_264_12"></a>Issue 6</h4><blockquote><p>The DESCRIPTION is updated to avoid use of the term "must" for application requirements.</p><p>A note indicating that this function need not be reentrant is added to the DESCRIPTION.</p></blockquote><div class="box"><em>End of informative text.</em></div><hr><hr size="2" noshade><center><font size="2"><!--footer start-->UNIX ® is a registered Trademark of The Open Group.<br>POSIX ® is a registered Trademark of The IEEE.<br>[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href="../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>]</font></center><!--footer end--><hr size="2" noshade></body></html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -