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);
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22 The hcreate(), hdestroy(), and hsearch() functions shall manage hash
23 search tables.
24 The hcreate() function shall allocate sufficient space for the table,
26 and the application shall ensure it is called before hsearch() is used.
27 The nel argument is an estimate of the maximum number of entries that
28 the table shall contain. This number may be adjusted upward by the
29 algorithm in order to obtain certain mathematically favorable circum‐
30 stances.
31 The hdestroy() function shall dispose of the search table, and may be
33 followed by another call to hcreate(). After the call to hdestroy(),
34 the data can no longer be considered accessible.
35 The hsearch() function is a hash-table search routine. It shall return
37 a pointer into a hash table indicating the location at which an entry
38 can be found. The item argument is a structure of type ENTRY (defined
39 in the <search.h> header) containing two pointers: item.key points to
40 the comparison key (a char *), and item.data (a void *) points to any
41 other data to be associated with that key. The comparison function used
42 by hsearch() is strcmp(). The action argument is a member of an enu‐
43 meration type ACTION indicating the disposition of the entry if it can‐
44 not be found in the table. ENTER indicates that the item should be
45 inserted in the table at an appropriate point. FIND indicates that no
46 entry should be made. Unsuccessful resolution is indicated by the
47 return of a null pointer.
48 These functions need not be thread-safe.
50
52 The hcreate() function shall return 0 if it cannot allocate sufficient
53 space for the table; otherwise, it shall return non-zero.
54 The hdestroy() function shall not return a value.
56 The hsearch() function shall return a null pointer if either the action
58 is FIND and the item could not be found or the action is ENTER and the
59 table is full.
60
62 The hcreate() and hsearch() functions may fail if:
63 ENOMEM Insufficient storage space is available.
65 The following sections are informative.
67
69 The following example reads in strings followed by two numbers and
70 stores them in a hash table, discarding duplicates. It then reads in
71 strings and finds the matching entry in the hash table and prints it
72 out.
73 #include <stdio.h>
76 #include <search.h>
77 #include <string.h>
78 struct info { /* This is the info stored in the table */
80 int age, room; /* other than the key. */
81 };
82 #define NUM_EMPL 5000 /* # of elements in search table. */
84 int main(void)
86 {
87 char string_space[NUM_EMPL*20]; /* Space to store strings. */
88 struct info info_space[NUM_EMPL]; /* Space to store employee info. */
89 char *str_ptr = string_space; /* Next space in string_space. */
90 struct info *info_ptr = info_space;
91 /* Next space in info_space. */
92 ENTRY item;
93 ENTRY *found_item; /* Name to look for in table. */
94 char name_to_find[30];
95 int i = 0;
97 /* Create table; no error checking is performed. */
99 (void) hcreate(NUM_EMPL);
100 while (scanf("%s%d%d", str_ptr, &info_ptr->age,
101 &info_ptr->room) != EOF && i++ < NUM_EMPL) {
102 /* Put information in structure, and structure in item. */
104 item.key = str_ptr;
105 item.data = info_ptr;
106 str_ptr += strlen(str_ptr) + 1;
107 info_ptr++;
108 /* Put item into table. */
110 (void) hsearch(item, ENTER);
111 }
112 /* Access table. */
114 item.key = name_to_find;
115 while (scanf("%s", item.key) != EOF) {
116 if ((found_item = hsearch(item, FIND)) != NULL) {
117 /* If item is in the table. */
119 (void)printf("found %s, age = %d, room = %d\n",
120 found_item->key,
121 ((struct info *)found_item->data)->age,
122 ((struct info *)found_item->data)->room);
123 } else
124 (void)printf("no such employee %s\n", name_to_find);
125 }
126 return 0;
127 }
128
130 The hcreate() and hsearch() functions may use malloc() to allocate
131 space.
132
134 None.
135
137 None.
138
140 bsearch(), lsearch(), malloc(), strcmp(), tdelete()
141 The Base Definitions volume of POSIX.1‐2017, <search.h>
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145 Portions of this text are reprinted and reproduced in electronic form
146 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
147 table Operating System Interface (POSIX), The Open Group Base Specifi‐
148 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
149 Electrical and Electronics Engineers, Inc and The Open Group. In the
150 event of any discrepancy between this version and the original IEEE and
151 The Open Group Standard, the original IEEE and The Open Group Standard
152 is the referee document. The original Standard can be obtained online
153 at http://www.opengroup.org/unix/online.html .
154 Any typographical or formatting errors that appear in this page are
156 most likely to have been introduced during the conversion of the source
157 files to man page format. To report such errors, see https://www.ker‐
158 nel.org/doc/man-pages/reporting_bugs.html .
159IEEE/The Open Group 2017 HCREATE(3P)