HCREATE(3) Library Functions Manual HCREATE(3)

hcreate, hcreate_r, hdestroy, hdestroy1, hdestroy_r, hdestroy1_r, hsearch, hsearch_r — manage hash search table

Standard C Library (libc, -lc)

#include <search.h>

int
hcreate(size_t nel);

int
hcreate_r(size_t nel, struct hsearch_data *table);

void
hdestroy(void);

void
hdestroy1(void (*freekey)(void *), void (*freedata)(void *));

void
hdestroy_r(struct hsearch_data *table);

void
hdestroy1_r(struct hsearch_data *table, void (*freekey)(void *), void (*freedata)(void *));

ENTRY *
hsearch(ENTRY item, ACTION action);

int
hsearch_r(ENTRY item, ACTION action, ENTRY ** itemp, struct hsearch_data *table);

The (), hcreate_r(), hdestroy(), hdestroy_r() hdestroy1(), hdestroy1_r() hsearch(), and hsearch_r() functions manage hash search tables.

The () function allocates and initializes the table. The nel argument specifies an estimate of the maximum number of entries to be held by the table. Unless further memory allocation fails, supplying an insufficient nel value will not result in functional harm, although a performance degradation may occur. Initialization using the hcreate() function is mandatory prior to any access operations using hsearch().

The () function destroys a table previously created using hcreate(). After a call to hdestroy(), the data can no longer be accessed.

The () function is used to search the hash table. It returns a pointer into the hash table indicating the address of an item. The item argument is of type ENTRY, defined in the <search.h> header. This is a structure type that contains two pointers:

char *key
comparison key
void *data
pointer to data associated with key

The key comparison function used by () is strcmp(3).

The action argument is of type ACTION, an enumeration type which defines the following values:

Insert item into the hash table. If an existing item with the same key is found, it is not replaced. Note that the key and data elements of item are used directly by the new table entry. The storage for the key must not be modified during the lifetime of the hash table.
Search the hash table without inserting item.

The traditional () and () functions don't free(3) the data associated with the key and value of each entry, because they did not allocate them. Since there is no “iterator” function provided, the () and hdestroy1_r() allow controlling how the key or value will be freed using the provided functions in the freekey and freedata arguments. If they are NULL, then key and value are not freed.

The (), (), (), and () functions are re-entrant versions of the above functions that can operate on a table supplied by the user. The hsearch_r() function returns 0 if the action is ENTER and the element cannot be created, 1 otherwise. If the element exists or can be created, it will be placed in itemp, otherwise itemp will be set to NULL.

If successful, the hcreate() and hcreate_r() functions return a non-zero value. Otherwise, a value of 0 is returned and errno is set to indicate the error.

The hdestroy() and hdestroy_r() functions return no value.

If successful, the hsearch() function returns a pointer to hash table entry matching the provided key. If the action is FIND and the item was not found, or if the action is ENTER and the insertion failed, NULL is returned and errno is set to indicate the error. If the action is ENTER and an entry already existed in the table matching the given key, the existing entry is returned and is not replaced.

The hsearch_r() function returns 1 unless the table is full, when it returns 0. If hsearch() returns 0 or the element is not found, errno is set to indicate the error.

The hcreate(), hcreate_r(), hsearch() and hsearch_r() functions will fail if:

[]
Insufficient memory is available.

The hsearch() and hsearch_r() functions will also fail if the action is FIND and the element is not found:

[]
The item given is not found.

bsearch(3), free(3), lsearch(3), malloc(3), strcmp(3)

The hcreate(), hdestroy() and hsearch() functions conform to X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”).

The hcreate(), hdestroy() and hsearch() functions first appeared in AT&T System V UNIX. The hcreate_r(), hdestroy_r(), and hsearch_r() functions are GNU extensions. The hdestroy1() and hdestroy1_r() are NetBSD extensions.

At least the following limitations can be mentioned:

February 7, 2017 NetBSD 11.0