1HCREATE(3P) POSIX Programmer's Manual HCREATE(3P)
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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.
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13 hcreate, hdestroy, hsearch — manage hash search table
14
16 #include <search.h>
17 int hcreate(size_t nel);
19 void hdestroy(void);
20 ENTRY *hsearch(ENTRY item, ACTION action);
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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 enu‐
44 meration type ACTION indicating the disposition of the entry if it can‐
45 not be found in the table. ENTER indicates that the item should be
46 inserted in the table at an appropriate point. FIND indicates that no
47 entry should be made. Unsuccessful resolution is indicated by the
48 return of a null pointer.
49 These functions need not be thread-safe.
51
53 The hcreate() function shall return 0 if it cannot allocate sufficient
54 space for the table; otherwise, it shall return non-zero.
55 The hdestroy() function shall not return a value.
57 The hsearch() function shall return a null pointer if either the action
59 is FIND and the item could not be found or the action is ENTER and the
60 table is full.
61
63 The hcreate() and hsearch() functions may fail if:
64 ENOMEM Insufficient storage space is available.
66 The following sections are informative.
68
70 The following example reads in strings followed by two numbers and
71 stores them in a hash table, discarding duplicates. It then reads in
72 strings and finds the matching entry in the hash table and prints it
73 out.
74 #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.1‐2008, <search.h>
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145 Portions of this text are reprinted and reproduced in electronic form
146 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
147 -- Portable Operating System Interface (POSIX), The Open Group Base
148 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
149 cal and Electronics Engineers, Inc and The Open Group. (This is
150 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
151 event of any discrepancy between this version and the original IEEE and
152 The Open Group Standard, the original IEEE and The Open Group Standard
153 is the referee document. The original Standard can be obtained online
154 at http://www.unix.org/online.html .
155 Any typographical or formatting errors that appear in this page are
157 most likely to have been introduced during the conversion of the source
158 files to man page format. To report such errors, see https://www.ker‐
159 nel.org/doc/man-pages/reporting_bugs.html .
160IEEE/The Open Group 2013 HCREATE(3P)