NAME    [Toc]    [Back]

     hcreate, hdestroy, hsearch - manage hash search table

LIBRARY    [Toc]    [Back]

     Standard C Library (libc, -lc)

SYNOPSIS    [Toc]    [Back]

     #include <search.h>

     int
     hcreate(size_t nel);

     void
     hdestroy(void);

     ENTRY *
     hsearch(ENTRY item, ACTION action);

DESCRIPTION    [Toc]    [Back]

     The hcreate(), hdestroy() and hsearch() functions manage hash search
     tables.

     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
     accessed.

     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
     members:
           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.

RETURN VALUES    [Toc]    [Back]

     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.

ERRORS    [Toc]    [Back]

     The hcreate() and hsearch() functions will fail if:

     [ENOMEM]           Insufficient memory is available.

SEE ALSO    [Toc]    [Back]

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

STANDARDS    [Toc]    [Back]

     The hcreate(), hdestroy() and hsearch() functions conform to X/Open
     Portability Guide Issue 4.2 (``XPG4.2'').

HISTORY    [Toc]    [Back]

     The hcreate(), hdestroy() and hsearch() functions first appeared in AT&T
     System V UNIX.

BUGS    [Toc]    [Back]

     The interface permits the use of only one hash table at a time.

BSD                            February 13, 2001                           BSD