man3/tsearch.3

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  24 .TH TSEARCH 3  1995-09-24 "GNU" "Linux Programmer's Manual"
  25 .SH NAME
  26 tsearch, tfind, tdelete, twalk, tdestroy \- manage a binary tree
  27 .SH SYNOPSIS
  28 .nf
  29 .B #include <search.h>
  30 .sp
  31 .BI "void *tsearch(const void *" key ", void **" rootp ,
  32 .BI "                int (*" compar ")(const void *, const void *));"
  33 .sp
  34 .BI "void *tfind(const void *" key ", const void **" rootp ,
  35 .BI "                int (*" compar ")(const void *, const void *));"
  36 .sp
  37 .BI "void *tdelete(const void *" key ", void **" rootp ,
  38 .BI "                int (*" compar ")(const void *, const void *));"
  39 .sp
  40 .BI "void twalk(const void *" root ", void (*" action ")(const void *" nodep ,
  41 .BI "                                   const VISIT " which ,
  42 .BI "                                   const int " depth "));"
  43 .sp
  44 .B #define _GNU_SOURCE
  45 .br
  46 .B #include <search.h>
  47 .sp
  48 .BI "void tdestroy(void *" root ", void (*" free_node ")(void *" nodep ));
  49 .RE
  50 .fi
  51 .SH DESCRIPTION
  52 \fBtsearch\fP(), \fBtfind\fP(), \fBtwalk\fP(), and \fBtdelete\fP() manage a
  53 binary tree.
  54 They are generalized from Knuth (6.2.2) Algorithm T.
  55 The first field in each node of the tree is a pointer to the
  56 corresponding data item.
  57 (The calling program must store the actual data.)
  58 \fIcompar\fP points to a comparison routine, which takes
  59 pointers to two items.
  60 It should return an integer which is negative,
  61 zero, or positive, depending on whether the first item is less than,
  62 equal to, or greater than the second.
  63 .PP
  64 \fBtsearch\fP() searches the tree for an item.
  65 \fIkey\fP points to the item to be searched for.
  66 \fIrootp\fP points to a variable which points to the root of the tree.
  67 If the tree is empty,
  68 then the variable that \fIrootp\fP points to should be set to NULL.
  69 If the item is found in the tree, then \fBtsearch\fP() returns a pointer
  70 to it.
  71 If it is not found, then \fBtsearch\fP() adds it, and returns a
  72 pointer to the newly added item.
  73 .PP
  74 \fBtfind\fP() is like \fBtsearch\fP(), except that if the item is not
  75 found, then \fBtfind\fP() returns NULL.
  76 .PP
  77 \fBtdelete\fP() deletes an item from the tree.
  78 Its arguments are the same as for \fBtsearch\fP().
  79 .PP
  80 \fBtwalk\fP() performs depth-first, left-to-right traversal of a binary
  81 tree.  \fIroot\fP points to the starting node for the traversal.
  82 If that node is not the root, then only part of the tree will be visited.
  83 \fBtwalk\fP() calls the user function \fIaction\fP each time a node is
  84 visited (that is, three times for an internal node, and once for a
  85 leaf).  \fIaction\fP, in turn, takes three arguments.
  86 The first is a pointer to the node being visited.
  87 The second is an integer which
  88 takes on the values \fBpreorder\fP, \fBpostorder\fP, and
  89 \fBendorder\fP depending on whether this is the first, second, or
  90 third visit to the internal node, or \fBleaf\fP if it is the single
  91 visit to a leaf node.
  92 (These symbols are defined in \fI<search.h>\fP.)
  93 The third argument is the depth of the node, with
  94 zero being the root.
  95 .PP
  96 (More commonly, \fBpreorder\fP, \fBpostorder\fP, and \fBendorder\fP
  97 are known as \fBpreorder\fP, \fBinorder\fP, and \fBpostorder\fP:
  98 before visiting the children, after the first and before the second,
  99 and after visiting the children.
 100 Thus, the choice of name \fBpost\%order\fP
 101 is rather confusing.)
 102 .PP
 103 \fBtdestroy\fP() removes the whole tree pointed to by \fIroot\fP,
 104 freeing all resources allocated by the \fBtsearch\fP() function.
 105 For the data in each tree node the function \fIfree_node\fP is called.
 106 The pointer to the data is passed as the argument to the function.
 107 If no such work is necessary \fIfree_node\fP must point to a function
 108 doing nothing.
 109 .SH "RETURN VALUE"
 110 \fBtsearch\fP() returns a pointer to a matching item in the tree, or to
 111 the newly added item, or NULL if there was insufficient memory
 112 to add the item.  \fBtfind\fP() returns a pointer to the item, or
 113 NULL if no match is found.
 114 If there are multiple elements that match the key,
 115 the element returned is unspecified.
 116 .PP
 117 \fBtdelete\fP() returns a pointer to the parent of the item deleted, or
 118 NULL if the item was not found.
 119 .PP
 120 \fBtsearch\fP(), \fBtfind\fP(), and \fBtdelete\fP() also
 121 return NULL if \fIrootp\fP was NULL on entry.
 122 .SH WARNINGS
 123 \fBtwalk\fP() takes a pointer to the root, while the other functions
 124 take a pointer to a variable which points to the root.
 125 .PP
 126 \fBtwalk\fP() uses \fBpostorder\fP to mean "after the left subtree, but
 127 before the right subtree".
 128 Some authorities would call this
 129 "inorder", and reserve "postorder" to mean "after both subtrees".
 130 .PP
 131 \fBtdelete\fP() frees the memory required for the node in the tree.
 132 The user is responsible for freeing the memory for the corresponding
 133 data.
 134 .PP
 135 The example program depends on the fact that \fBtwalk\fP() makes no
 136 further reference to a node after calling the user function with
 137 argument "endorder" or "leaf".
 138 This works with the GNU library
 139 implementation, but is not in the SysV documentation.
 140 .SH EXAMPLE
 141 The following program inserts twelve random numbers into a binary
 142 tree, where duplicate numbers are collapsed, then prints the numbers
 143 in order.
 144 .sp
 145 .nf
 146 #include <search.h>
 147 #include <stdlib.h>
 148 #include <stdio.h>
 149 #include <time.h>
 150
 151 void *root = NULL;
 152
 153 void *
 154 xmalloc(unsigned n)
 155 {
 156     void *p;
 157     p = malloc(n);
 158     if (p)
 159         return p;
 160     fprintf(stderr, "insufficient memory\\n");
 161     exit(1);
 162 }
 163
 164 int
 165 compare(const void *pa, const void *pb)
 166 {
 167     if (*(int *) pa < *(int *) pb)
 168         return \-1;
 169     if (*(int *) pa > *(int *) pb)
 170         return 1;
 171     return 0;
 172 }
 173
 174 void
 175 action(const void *nodep, const VISIT which, const int depth)
 176 {
 177     int *datap;
 178
 179     switch(which) {
 180     case preorder:
 181         break;
 182     case postorder:
 183         datap = *(int **)nodep;
 184         printf("%6d\\n", *datap);
 185         break;
 186     case endorder:
 187         break;
 188     case leaf:
 189         datap = *(int **) nodep;
 190         printf("%6d\\n", *datap);
 191         break;
 192     }
 193 }
 194
 195 int
 196 main(void)
 197 {
 198     int i, *ptr;
 199     void *val;
 200
 201     srand(time(NULL));
 202     for (i = 0; i < 12; i++) {
 203         ptr = (int *) xmalloc(sizeof(int));
 204         *ptr = rand() & 0xff;
 205         val = tsearch((void *) ptr, &root, compare);
 206         if (val == NULL)
 207             exit(1);
 208     }
 209     twalk(root, action);
 210     return 0;
 211 }
 212 .fi
 213 .SH "CONFORMING TO"
 214 SVr4, POSIX.1-2001.
 215 The function
 216 .BR tdestroy ()
 217 is a GNU extension.
 218 .SH "SEE ALSO"
 219 .BR bsearch (3),
 220 .BR hsearch (3),
 221 .BR lsearch (3),
 222 .BR qsort (3),
 223 .BR feature_test_macros (7)