hsearch, hcreate, hdestroy, hsearch_r, hcreate_r, hdestroy_r
- Manage hash tables
#include <search.h>
ENTRY *hsearch(
ENTRY item,
ACTION action ); int hcreate(
size_t nel ); void hdestroy(
void ); int hsearch_r(
ENTRY item,
ACTION action,
ENTRY **target,
struct hsearch_data *hsearch_data ); int hcreate_r(
size_t nel,
struct hsearch_data *hsearch_data ); void hdestroy_r(
struct hsearch_data *hsearch_data );
Standard C Library (libc)
Interfaces documented on this reference page conform to
industry standards as follows:
hsearch(), hcreate(), hdestroy(): XSH4.2
Refer to the standards(5) reference page for more information
about industry standards and associated tags.
Identifies a structure of the type ENTRY as defined in the
search.h header file. It contains two pointers: Points to
the comparison key string. Points to any other data associated
with the char *key parameter.
Pointers to types other than char should be cast as
char *. Specifies a value for an ACTION enum type,
which indicates what is to be done with an item key
when it cannot be found in the hash table. The following
two actions can be specified for this parameter:
Enter the key specified by the item parameter
into the hash table at the appropriate place. When
the table is full, a null pointer is returned. Do
not enter the item key into the table, but return a
null pointer when an item key cannot be found in
the hash table. Specifies an estimate of the maximum
number of entries that the hash table will contain.
Under some circumstances, the hcreate() function
may make the hash table larger than specified
to obtain mathematically favorable conditions for
access to the hash table. Points at the hash
table. This table is kept in the thread's address
space. Points at the size of the hash table.
Points at the log base 2 version of the hash table
length. Points at the number of entries in the
hash table. Specifies the length of the hash
table. Specifies the log base 2 version of the
hash table length. Points to the item actually
found. Consists of data for the hash table.
The hsearch(), hcreate(), and hdestroy() functions are
used to manage hash table operations: The hcreate() function
initializes the hash table. You must call the hcreate()
function before calling the hsearch() function. The
hsearch() function searches a hash table. It returns a
pointer into a hash table that indicates where a given
entry can be found. The hsearch() function uses open
addressing with a hash function. The hdestroy() function
deletes the hash table. This allows you to start a new
hash table because only one table may be active at a time.
After the call to hdestroy(), the hash table data should
no longer be considered accessible.
[Tru64 UNIX] The hsearch_r(), hcreate_r(), and hdestroy_r()
functions are reentrant versions of hsearch(),
hcreate(), and hdestroy(). Upon successful completion,
the hsearch_r() function returns 0 (zero). Upon failure,
it returns -1 and sets errno.
[Tru64 UNIX] Threads can share hash tables by using the
hcreate_r, hsearch_r, and hdestroy_r functions with a common
hsearch_data value. To prevent corruption of data when
sharing a hash table, locks must be used around calls that
use the common hsearch_data value.
The hsearch() function returns a null pointer when the
action parameter is FIND and the key pointed to by item
cannot be found or when the specified action is ENTER and
the hash table is full.
Upon successful completion, the hcreate() function returns
a nonzero value. Otherwise, when sufficient space for the
table cannot be allocated, the hcreate() function returns
a value of 0 (zero).
If any of the following conditions occur, the hsearch()
function sets errno to the corresponding value: The table
is full. [Tru64 UNIX] The search failed.
Functions: bsearch(3), lsearch(3), tsearch(3), qsort(3)
Standards: standards(5)
hsearch(3)
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