1HCREATE(3P) POSIX Programmer's Manual HCREATE(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 hcreate, hdestroy, hsearch - manage hash search table
13
15 #include <search.h>
16 int hcreate(size_t nel);
18 void hdestroy(void);
19 ENTRY *hsearch(ENTRY item, ACTION action);
20
23 The hcreate(), hdestroy(), and hsearch() functions shall manage hash
24 search tables.
25 The hcreate() function shall allocate sufficient space for the table,
27 and the application shall ensure it is called before hsearch() is used.
28 The nel argument is an estimate of the maximum number of entries that
29 the table shall contain. This number may be adjusted upward by the
30 algorithm in order to obtain certain mathematically favorable circum‐
31 stances.
32 The hdestroy() function shall dispose of the search table, and may be
34 followed by another call to hcreate(). After the call to hdestroy(),
35 the data can no longer be considered accessible.
36 The hsearch() function is a hash-table search routine. It shall return
38 a pointer into a hash table indicating the location at which an entry
39 can be found. The item argument is a structure of type ENTRY (defined
40 in the <search.h> header) containing two pointers: item.key points to
41 the comparison key (a char *), and item.data (a void *) points to any
42 other data to be associated with that key. The comparison function used
43 by hsearch() is strcmp(). The action argument is a member of an enumer‐
44 ation type ACTION indicating the disposition of the entry if it cannot
45 be found in the table. ENTER indicates that the item should be inserted
46 in the table at an appropriate point. FIND indicates that no entry
47 should be made. Unsuccessful resolution is indicated by the return of
48 a null pointer.
49 These functions need not be reentrant. A function that is not required
51 to be reentrant is not required to be thread-safe.
52
54 The hcreate() function shall return 0 if it cannot allocate sufficient
55 space for the table; otherwise, it shall return non-zero.
56 The hdestroy() function shall not return a value.
58 The hsearch() function shall return a null pointer if either the action
60 is FIND and the item could not be found or the action is ENTER and the
61 table is full.
62
64 The hcreate() and hsearch() functions may fail if:
65 ENOMEM Insufficient storage space is available.
67 The following sections are informative.
70
72 The following example reads in strings followed by two numbers and
73 stores them in a hash table, discarding duplicates. It then reads in
74 strings and finds the matching entry in the hash table and prints it
75 out.
76 #include <stdio.h>
79 #include <search.h>
80 #include <string.h>
81 struct info { /* This is the info stored in the table */
84 int age, room; /* other than the key. */
85 };
86 #define NUM_EMPL 5000 /* # of elements in search table. */
89 int main(void)
93 {
94 char string_space[NUM_EMPL*20]; /* Space to store strings. */
95 struct info info_space[NUM_EMPL]; /* Space to store employee info. */
96 char *str_ptr = string_space; /* Next space in string_space. */
97 struct info *info_ptr = info_space;
98 /* Next space in info_space. */
99 ENTRY item;
100 ENTRY *found_item; /* Name to look for in table. */
101 char name_to_find[30];
102 int i = 0;
105 /* Create table; no error checking is performed. */
108 (void) hcreate(NUM_EMPL);
109 while (scanf("%s%d%d", str_ptr, &info_ptr->age,
110 &info_ptr->room) != EOF && i++ < NUM_EMPL) {
111 /* Put information in structure, and structure in item. */
114 item.key = str_ptr;
115 item.data = info_ptr;
116 str_ptr += strlen(str_ptr) + 1;
117 info_ptr++;
118 /* Put item into table. */
121 (void) hsearch(item, ENTER);
122 }
123 /* Access table. */
126 item.key = name_to_find;
127 while (scanf("%s", item.key) != EOF) {
128 if ((found_item = hsearch(item, FIND)) != NULL) {
129 /* If item is in the table. */
132 (void)printf("found %s, age = %d, room = %d\n",
133 found_item->key,
134 ((struct info *)found_item->data)->age,
135 ((struct info *)found_item->data)->room);
136 } else
137 (void)printf("no such employee %s\n", name_to_find);
138 }
139 return 0;
140 }
141
143 The hcreate() and hsearch() functions may use malloc() to allocate
144 space.
145
147 None.
148
150 None.
151
153 bsearch(), lsearch(), malloc(), strcmp(), tsearch(), the Base Defini‐
154 tions volume of IEEE Std 1003.1-2001, <search.h>
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157 Portions of this text are reprinted and reproduced in electronic form
158 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
159 -- Portable Operating System Interface (POSIX), The Open Group Base
160 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
161 Electrical and Electronics Engineers, Inc and The Open Group. In the
162 event of any discrepancy between this version and the original IEEE and
163 The Open Group Standard, the original IEEE and The Open Group Standard
164 is the referee document. The original Standard can be obtained online
165 at http://www.opengroup.org/unix/online.html .
166IEEE/The Open Group 2003 HCREATE(3P)