hcreate, hdestroy, hsearch - manage hash search table
Standard C Library (libc, -lc)
hsearch(ENTRY item, ACTION action);
The hcreate(), hdestroy() and hsearch() functions manage hash search
The hcreate() 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 hdestroy() function destroys a table previously created using
hcreate(). After a call to hdestroy(), the data can no longer be
The hsearch() function is used to search to the hash table. It returns a
pointer into the hash table indicating the address of an item. The item
argument is of type ENTRY, a structural type which contains the following
char *key comparison key.
void *data pointer to data associated with key.
The key comparison function used by hsearch() is strcmp(3).
The action argument is of type ACTION, an enumeration type which defines
the following values:
ENTER 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.
FIND Search the hash table without inserting item.
If successful, the hcreate() function returns a non-zero value. Otherwise,
a value of 0 is returned and errno is set to indicate the error.
The hdestroy() functions returns 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 hcreate() and hsearch() functions will fail if:
[ENOMEM] Insufficient memory is available.
bsearch(3), lsearch(3), malloc(3), strcmp(3)
The hcreate(), hdestroy() and hsearch() functions conform to X/Open
Portability Guide Issue 4.2 (``XPG4.2'').
The hcreate(), hdestroy() and hsearch() functions first appeared in AT&T
System V UNIX.
The interface permits the use of only one hash table at a time.
BSD February 13, 2001 BSD
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