258 lines
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258 lines
11 KiB
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<title>tdelete</title>
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<basefont size="3"> <a name="tdelete"></a> <a name="tag_03_770"></a><!-- tdelete -->
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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_770_01"></a>NAME</h4>
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<blockquote>tdelete, tfind, tsearch, twalk - manage a binary search tree</blockquote>
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<h4><a name="tag_03_770_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 *tdelete(const void *restrict</tt> <i>key</i><tt>, void **restrict</tt> <i>rootp</i><tt>,<br>
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int(*</tt><i>compar</i><tt>)(const void *, const void *));<br>
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void *tfind(const void *</tt><i>key</i><tt>, void *const *</tt><i>rootp</i><tt>,<br>
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int(*</tt><i>compar</i><tt>)(const void *, const void *));<br>
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void *tsearch(const void *</tt><i>key</i><tt>, void **</tt><i>rootp</i><tt>,<br>
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int (*</tt><i>compar</i><tt>)(const void *, const void *));<br>
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void twalk(const void *</tt><i>root</i><tt>,<br>
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void (*</tt><i>action</i><tt>)(const void *, VISIT, int)); <img src="../images/opt-end.gif"
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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_770_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>tdelete</i>(), <i>tfind</i>(), <i>tsearch</i>(), and <i>twalk</i>() functions manipulate binary search trees. Comparisons
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are made with a user-supplied routine, the address of which is passed as the <i>compar</i> argument. This routine is called with
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two arguments, which are the pointers to the elements being compared. The application shall ensure that the user-supplied routine
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returns an integer less than, equal to, or greater than 0, according to whether the first argument is to be considered less than,
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equal to, or greater than the second argument. The comparison function need not compare every byte, so arbitrary data may be
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contained in the elements in addition to the values being compared.</p>
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<p>The <i>tsearch</i>() function shall build and access the tree. The <i>key</i> argument is a pointer to an element to be accessed
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or stored. If there is a node in the tree whose element is equal to the value pointed to by <i>key</i>, a pointer to this found
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node shall be returned. Otherwise, the value pointed to by <i>key</i> shall be inserted (that is, a new node is created and the
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value of <i>key</i> is copied to this node), and a pointer to this node returned. Only pointers are copied, so the application
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shall ensure that the calling routine stores the data. The <i>rootp</i> argument points to a variable that points to the root node
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of the tree. A null pointer value for the variable pointed to by <i>rootp</i> denotes an empty tree; in this case, the variable
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shall be set to point to the node which shall be at the root of the new tree.</p>
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<p>Like <i>tsearch</i>(), <i>tfind</i>() shall search for a node in the tree, returning a pointer to it if found. However, if it is
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not found, <i>tfind</i>() shall return a null pointer. The arguments for <i>tfind</i>() are the same as for <i>tsearch</i>().</p>
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<p>The <i>tdelete</i>() function shall delete a node from a binary search tree. The arguments are the same as for <i>tsearch</i>().
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The variable pointed to by <i>rootp</i> shall be changed if the deleted node was the root of the tree. The <i>tdelete</i>()
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function shall return a pointer to the parent of the deleted node, or a null pointer if the node is not found.</p>
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<p>The <i>twalk</i>() function shall traverse a binary search tree. The <i>root</i> argument is a pointer to the root node of the
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tree to be traversed. (Any node in a tree may be used as the root for a walk below that node.) The argument <i>action</i> is the
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name of a routine to be invoked at each node. This routine is, in turn, called with three arguments. The first argument shall be
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the address of the node being visited. The structure pointed to by this argument is unspecified and shall not be modified by the
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application, but it shall be possible to cast a pointer-to-node into a pointer-to-pointer-to-element to access the element stored
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in the node. The second argument shall be a value from an enumeration data type:</p>
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<pre>
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<tt>typedef enum { preorder, postorder, endorder, leaf } VISIT;
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</tt>
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</pre>
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<p>(defined in <a href="../basedefs/search.h.html"><i><search.h></i></a>), depending on whether this is the first, second, or
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third time that the node is visited (during a depth-first, left-to-right traversal of the tree), or whether the node is a leaf. The
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third argument shall be the level of the node in the tree, with the root being level 0.</p>
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<p>If the calling function alters the pointer to the root, the result is undefined.</p>
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</blockquote>
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<h4><a name="tag_03_770_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>If the node is found, both <i>tsearch</i>() and <i>tfind</i>() shall return a pointer to it. If not, <i>tfind</i>() shall return
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a null pointer, and <i>tsearch</i>() shall return a pointer to the inserted item.</p>
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<p>A null pointer shall be returned by <i>tsearch</i>() if there is not enough space available to create a new node.</p>
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<p>A null pointer shall be returned by <i>tdelete</i>(), <i>tfind</i>(), and <i>tsearch</i>() if <i>rootp</i> is a null pointer on
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entry.</p>
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<p>The <i>tdelete</i>() function shall return a pointer to the parent of the deleted node, or a null pointer if the node is not
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found.</p>
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<p>The <i>twalk</i>() function shall not return a value.</p>
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</blockquote>
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<h4><a name="tag_03_770_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_770_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>The following code reads in strings and stores structures containing a pointer to each string and a count of its length. It then
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walks the tree, printing out the stored strings and their lengths in alphabetical order.</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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#include <stdio.h>
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<br>
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#define STRSZ 10000
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#define NODSZ 500
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<br>
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struct node { /* Pointers to these are stored in the tree. */
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char *string;
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int length;
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};
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<br>
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char string_space[STRSZ]; /* Space to store strings. */
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struct node nodes[NODSZ]; /* Nodes to store. */
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void *root = NULL; /* This points to the root. */
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<br>
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int main(int argc, char *argv[])
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{
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char *strptr = string_space;
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struct node *nodeptr = nodes;
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void print_node(const void *, VISIT, int);
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int i = 0, node_compare(const void *, const void *);
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<br>
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while (gets(strptr) != NULL && i++ < NODSZ) {
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/* Set node. */
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nodeptr->string = strptr;
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nodeptr->length = strlen(strptr);
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/* Put node into the tree. */
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(void) tsearch((void *)nodeptr, (void **)&root,
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node_compare);
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/* Adjust pointers, so we do not overwrite tree. */
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strptr += nodeptr->length + 1;
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nodeptr++;
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}
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twalk(root, print_node);
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return 0;
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}
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<br>
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/*
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* This routine compares two nodes, based on an
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* alphabetical ordering of the string field.
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*/
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int
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node_compare(const void *node1, const void *node2)
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{
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return strcmp(((const struct node *) node1)->string,
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((const struct node *) node2)->string);
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}
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<br>
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/*
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* This routine prints out a node, the second time
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* twalk encounters it or if it is a leaf.
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*/
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void
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print_node(const void *ptr, VISIT order, int level)
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{
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const struct node *p = *(const struct node **) ptr;
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<br>
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if (order == postorder || order == leaf) {
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(void) printf("string = %s, length = %d\n",
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p->string, p->length);
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}
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}
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</tt>
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</pre>
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</blockquote>
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<h4><a name="tag_03_770_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The <i>root</i> argument to <i>twalk</i>() is one level of indirection less than the <i>rootp</i> arguments to <i>tdelete</i>()
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and <i>tsearch</i>().</p>
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<p>There are two nomenclatures used to refer to the order in which tree nodes are visited. The <i>tsearch</i>() function uses
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<b>preorder</b>, <b>postorder</b>, and <b>endorder</b> to refer respectively to visiting a node before any of its children, after
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its left child and before its right, and after both its children. The alternative nomenclature uses <b>preorder</b>,
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<b>inorder</b>, and <b>postorder</b> to refer to the same visits, which could result in some confusion over the meaning of
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<b>postorder</b>.</p>
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</blockquote>
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<h4><a name="tag_03_770_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_770_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_770_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="lsearch.html"><i>lsearch</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_770_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_770_12"></a>Issue 5</h4>
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<blockquote>
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<p>The last paragraph of the DESCRIPTION was included as an APPLICATION USAGE note in previous issues.</p>
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</blockquote>
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<h4><a name="tag_03_770_13"></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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<p>The <b>restrict</b> keyword is added to the <i>tdelete</i>() prototype for alignment with the ISO/IEC 9899:1999
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standard.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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POSIX ® is a registered Trademark of The IEEE.<br>
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