1HCREATE(P) POSIX Programmer's Manual HCREATE(P)
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6 hcreate, hdestroy, hsearch - manage hash search table
7
9 #include <search.h>
10 int hcreate(size_t nel);
12 void hdestroy(void);
13 ENTRY *hsearch(ENTRY item, ACTION action);
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17 The hcreate(), hdestroy(), and hsearch() functions shall manage hash
18 search tables.
19 The hcreate() function shall allocate sufficient space for the table,
21 and the application shall ensure it is called before hsearch() is used.
22 The nel argument is an estimate of the maximum number of entries that
23 the table shall contain. This number may be adjusted upward by the
24 algorithm in order to obtain certain mathematically favorable circum‐
25 stances.
26 The hdestroy() function shall dispose of the search table, and may be
28 followed by another call to hcreate(). After the call to hdestroy(),
29 the data can no longer be considered accessible.
30 The hsearch() function is a hash-table search routine. It shall return
32 a pointer into a hash table indicating the location at which an entry
33 can be found. The item argument is a structure of type ENTRY (defined
34 in the <search.h> header) containing two pointers: item.key points to
35 the comparison key (a char *), and item.data (a void *) points to any
36 other data to be associated with that key. The comparison function used
37 by hsearch() is strcmp(). The action argument is a member of an enumer‐
38 ation type ACTION indicating the disposition of the entry if it cannot
39 be found in the table. ENTER indicates that the item should be inserted
40 in the table at an appropriate point. FIND indicates that no entry
41 should be made. Unsuccessful resolution is indicated by the return of
42 a null pointer.
43 These functions need not be reentrant. A function that is not required
45 to be reentrant is not required to be thread-safe.
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48 The hcreate() function shall return 0 if it cannot allocate sufficient
49 space for the table; otherwise, it shall return non-zero.
50 The hdestroy() function shall not return a value.
52 The hsearch() function shall return a null pointer if either the action
54 is FIND and the item could not be found or the action is ENTER and the
55 table is full.
56
58 The hcreate() and hsearch() functions may fail if:
59 ENOMEM Insufficient storage space is available.
61 The following sections are informative.
64
66 The following example reads in strings followed by two numbers and
67 stores them in a hash table, discarding duplicates. It then reads in
68 strings and finds the matching entry in the hash table and prints it
69 out.
70 #include <stdio.h>
73 #include <search.h>
74 #include <string.h>
75 struct info { /* This is the info stored in the table */
78 int age, room; /* other than the key. */
79 };
80 #define NUM_EMPL 5000 /* # of elements in search table. */
83 int main(void)
87 {
88 char string_space[NUM_EMPL*20]; /* Space to store strings. */
89 struct info info_space[NUM_EMPL]; /* Space to store employee info. */
90 char *str_ptr = string_space; /* Next space in string_space. */
91 struct info *info_ptr = info_space;
92 /* Next space in info_space. */
93 ENTRY item;
94 ENTRY *found_item; /* Name to look for in table. */
95 char name_to_find[30];
96 int i = 0;
99 /* Create table; no error checking is performed. */
102 (void) hcreate(NUM_EMPL);
103 while (scanf("%s%d%d", str_ptr, &info_ptr->age,
104 &info_ptr->room) != EOF && i++ < NUM_EMPL) {
105 /* Put information in structure, and structure in item. */
108 item.key = str_ptr;
109 item.data = info_ptr;
110 str_ptr += strlen(str_ptr) + 1;
111 info_ptr++;
112 /* Put item into table. */
115 (void) hsearch(item, ENTER);
116 }
117 /* Access table. */
120 item.key = name_to_find;
121 while (scanf("%s", item.key) != EOF) {
122 if ((found_item = hsearch(item, FIND)) != NULL) {
123 /* If item is in the table. */
126 (void)printf("found %s, age = %d, room = %d\n",
127 found_item->key,
128 ((struct info *)found_item->data)->age,
129 ((struct info *)found_item->data)->room);
130 } else
131 (void)printf("no such employee %s\n", name_to_find);
132 }
133 return 0;
134 }
135
137 The hcreate() and hsearch() functions may use malloc() to allocate
138 space.
139
141 None.
142
144 None.
145
147 bsearch() , lsearch() , malloc() , strcmp() , tsearch() , the Base Def‐
148 initions volume of IEEE Std 1003.1-2001, <search.h>
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151 Portions of this text are reprinted and reproduced in electronic form
152 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
153 -- Portable Operating System Interface (POSIX), The Open Group Base
154 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
155 Electrical and Electronics Engineers, Inc and The Open Group. In the
156 event of any discrepancy between this version and the original IEEE and
157 The Open Group Standard, the original IEEE and The Open Group Standard
158 is the referee document. The original Standard can be obtained online
159 at http://www.opengroup.org/unix/online.html .
160IEEE/The Open Group 2003 HCREATE(P)