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hsearch(3)						     Library Functions Manual							hsearch(3)

Name
       hsearch, hcreate, hdestroy - manage hash search tables

Syntax
       #include <search.h>

       ENTRY *hsearch (item, action)
       ENTRY item;
       ACTION action;

       int hcreate (nel)
       unsigned nel;

       void hdestroy ( )

Description
       The  subroutine is a hash-table search routine generalized from Knuth (6.4) Algorithm D.  It returns a pointer into a hash table indicating
       the location at which an entry can be found.  The item is a structure of type ENTRY (defined in the <search.h> header file) containing  two
       pointers: item.key points to the comparison key, and item.data points to any other data to be associated with that key.	(Pointers to types
       other than character should be cast to pointer-to-character.)  The action is a member of an enumeration type ACTION indicating the disposi-
       tion  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.

       The subroutine allocates sufficient space for the table, and must be called before is used.  The nel is an estimate of the  maximum  number
       of  entries  that  the  table  will contain.  This number may be adjusted upward by the algorithm in order to obtain certain mathematically
       favorable circumstances.

       The subroutine destroys the search table, and may be followed by another call to

Restrictions
       Only one hash search table may be active at any given time.

Diagnostics
       The subroutine returns 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 subroutine returns zero if it cannot allocate sufficient space for the table.

See Also
       bsearch(3), lsearch(3), string(3), tsearch(3)

																	hsearch(3)

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hsearch(3C)						   Standard C Library Functions 					       hsearch(3C)

NAME
hsearch, hcreate, hdestroy - manage hash search tables SYNOPSIS
#include <search.h> ENTRY *hsearch(ENTRY item, ACTION action); int hcreate(size_t mekments); void hdestroy(void); DESCRIPTION
The hsearch() function is a hash-table search routine generalized from Knuth (6.4) Algorithm D. It returns a pointer into a hash table indicating the location at which an entry can be found. The comparison function used by hsearch() is strcmp() (see string(3C)). 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, and item.data points to any other data to be associated with that key. (Pointers to types other than void should be cast to pointer-to- void.) The action argument is a member of an enumeration type ACTION (defined in <search.h>) 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. Given a duplicate of an existing item, the new item is not entered and hsearch() returns a pointer to the existing item. FIND indicates that no entry should be made. Unsuccessful resolution is indicated by the return of a null pointer. The hcreate() function allocates sufficient space for the table, and must be called before hsearch() is used. The nel argument is an esti- mate of the maximum number of entries that the table will contain. This number may be adjusted upward by the algorithm in order to obtain certain mathematically favorable circumstances. The hdestroy() function destroys the search table, and may be followed by another call to hcreate(). RETURN VALUES
The hsearch() function returns 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() function returns 0 if it cannot allocate sufficient space for the table. USAGE
The hsearch() and hcreate() functions use malloc(3C) to allocate space. Only one hash search table may be active at any given time. EXAMPLES
Example 1 Example to read in strings. The following example will read in strings followed by two numbers and store them in a hash table, discarding duplicates. It will then read in strings and find the matching entry in the hash table and print it. #include <stdio.h> #include <search.h> #include <string.h> #include <stdlib.h> struct info { /* this is the info stored in table */ int age, room; /* other than the key */ }; #define NUM_EMPL 5000 /* # of elements in search table */ main( ) { /* space to store strings */ char string_space[NUM_EMPL*20]; /* space to store employee info */ struct info info_space[NUM_EMPL]; /* next avail space in string_space */ char *str_ptr = string_space; /* next avail space in info_space */ struct info *info_ptr = info_space; ENTRY item, *found_item; /* name to look for in table */ char name_to_find[30]; int i = 0; /* create table */ (void) hcreate(NUM_EMPL); while (scanf("%s%d%d", str_ptr, &info_ptr->age, &info_ptr->room) != EOF && i++ < NUM_EMPL) { /* put info in structure, and structure in item */ item.key = str_ptr; item.data = (void *)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 ", found_item->key, ((struct info *)found_item->data)->age, ((struct info *)found_item->data)->room); } else { (void)printf("no such employee %s ", name_to_find) } } return 0; } ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Safe | +-----------------------------+-----------------------------+ SEE ALSO
bsearch(3C), lsearch(3C), malloc(3C), string(3C), tsearch(3C), malloc(3MALLOC), attributes(5), standards(5) The Art of Computer Programming, Volume 3, Sorting and Searching by Donald E. Knuth, published by Addison-Wesley Publishing Company, 1973. SunOS 5.11 29 Dec 1996 hsearch(3C)
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