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HCREATE(3P) POSIX Programmer's Manual HCREATE(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
hcreate, hdestroy, hsearch — manage hash search table
#include <search.h>
int hcreate(size_t nel);
void hdestroy(void);
ENTRY *hsearch(ENTRY item, ACTION action);
The hcreate(), hdestroy(), and hsearch() functions shall manage hash
search tables.
The hcreate() function shall allocate sufficient space for the table,
and the application shall ensure it is called before hsearch() is
used. The nel argument is an estimate of the maximum number of
entries that the table shall contain. This number may be adjusted
upward by the algorithm in order to obtain certain mathematically
favorable circumstances.
The hdestroy() function shall dispose of the search table, and may be
followed by another call to hcreate(). After the call to hdestroy(),
the data can no longer be considered accessible.
The hsearch() function is a hash-table search routine. It shall
return a pointer into a hash table indicating the location at which
an entry can be found. The item argument is a structure of type ENTRY
(defined in the <search.h> header) containing two pointers: item.key
points to the comparison key (a char *), and item.data (a void *)
points to any other data to be associated with that key. The
comparison function used by hsearch() is strcmp(). The action
argument is a member of an enumeration type ACTION indicating the
disposition of the entry if it cannot be found in the table. ENTER
indicates that the item should be inserted in the table at an
appropriate point. FIND indicates that no entry should be made.
Unsuccessful resolution is indicated by the return of a null pointer.
These functions need not be thread-safe.
The hcreate() function shall return 0 if it cannot allocate
sufficient space for the table; otherwise, it shall return non-zero.
The hdestroy() function shall not return a value.
The hsearch() function shall return a null pointer if either the
action is FIND and the item could not be found or the action is ENTER
and the table is full.
The hcreate() and hsearch() functions may fail if:
ENOMEM Insufficient storage space is available.
The following sections are informative.
The following example reads in strings followed by two numbers and
stores them in a hash table, discarding duplicates. It then reads in
strings and finds the matching entry in the hash table and prints it
out.
#include <stdio.h>
#include <search.h>
#include <string.h>
struct info { /* This is the info stored in the table */
int age, room; /* other than the key. */
};
#define NUM_EMPL 5000 /* # of elements in search table. */
int main(void)
{
char string_space[NUM_EMPL*20]; /* Space to store strings. */
struct info info_space[NUM_EMPL]; /* Space to store employee info. */
char *str_ptr = string_space; /* Next space in string_space. */
struct info *info_ptr = info_space;
/* Next space in info_space. */
ENTRY item;
ENTRY *found_item; /* Name to look for in table. */
char name_to_find[30];
int i = 0;
/* Create table; no error checking is performed. */
(void) hcreate(NUM_EMPL);
while (scanf("%s%d%d", str_ptr, &info_ptr−>age,
&info_ptr−>room) != EOF && i++ < NUM_EMPL) {
/* Put information in structure, and structure in item. */
item.key = str_ptr;
item.data = info_ptr;
str_ptr += strlen(str_ptr) + 1;
info_ptr++;
/* Put item into table. */
(void) hsearch(item, ENTER);
}
/* Access table. */
item.key = name_to_find;
while (scanf("%s", item.key) != EOF) {
if ((found_item = hsearch(item, FIND)) != NULL) {
/* If item is in the table. */
(void)printf("found %s, age = %d, room = %d\n",
found_item−>key,
((struct info *)found_item−>data)−>age,
((struct info *)found_item−>data)−>room);
} else
(void)printf("no such employee %s\n", name_to_find);
}
return 0;
}
The hcreate() and hsearch() functions may use malloc() to allocate
space.
None.
None.
bsearch(3p), lsearch(3p), malloc(3p), strcmp(3p), tdelete(3p)
The Base Definitions volume of POSIX.1‐2008, search.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 HCREATE(3P)
Pages that refer to this page: search.h(0p), bsearch(3p), lsearch(3p), tdelete(3p)