hsearch(3c) [hpux man page]
hsearch(3C) hsearch(3C) NAME
hsearch(), hcreate(), hdestroy() - manage hash search tables SYNOPSIS
DESCRIPTION
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. Only pointers are copied, so the calling routine must store the data (the value of the "key" must be unique). item is a structure of type (defined in the header file) containing two pointers: points to the comparison key, and points to any other data to be associated with that key. (Pointers to types other than character should be cast to pointer-to-character.) action is a member of an enumeration type indicating the disposition of the entry if it cannot be found in the table. indicates that the item should be inserted in the table at an appropriate point. indicates that no entry should be made. Unsuccessful resolution is indicated by the return of a NULL pointer. allocates sufficient space for the table, and must be called before is used. nel is an estimate of the maximum number of entries that the table will contain. This number can be adjusted upward by the algorithm in order to obtain certain mathematically favorable circumstances. destroys the search table, and can be followed by another call to EXAMPLE
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> 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 */ 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, *hsearch( ); /* 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 = (char *)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 VALUE
returns a NULL pointer if either the action is and the item could not be found or the action is and the table is full. returns zero if it cannot allocate sufficient space for the table. WARNINGS
and use to allocate space (see malloc(3C)). Only one hash search table can be active at any given time. SEE ALSO
bsearch(3C), lsearch(3C), malloc(3C), string(3C), tsearch(3C), thread_safety(5). STANDARDS CONFORMANCE
hsearch(3C)
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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 5.10 29 Dec 1996 hsearch(3C)