HPUX Hash[3]
Hash in anderen Kapiteln des hpux Handbuch:
Tcl_Hash(3) Tcl Tcl_Hash(3)
Tcl Library Procedures Tcl Library Procedures
___________________________________________________________________________
NAME
Tcl_InitHashTable, Tcl_DeleteHashTable, Tcl_CreateHashEntry,
Tcl_DeleteHashEntry, Tcl_FindHashEntry, Tcl_GetHashValue,
Tcl_SetHashValue, Tcl_GetHashKey, Tcl_FirstHashEntry,
Tcl_NextHashEntry, Tcl_HashStats - procedures to manage hash tables
SYNOPSIS
#include <tcl.h>
Tcl_InitHashTable(tablePtr, keyType)
Tcl_DeleteHashTable(tablePtr)
Tcl_HashEntry *
Tcl_CreateHashEntry(tablePtr, key, newPtr)
Tcl_DeleteHashEntry(entryPtr)
Tcl_HashEntry *
Tcl_FindHashEntry(tablePtr, key)
ClientData
Tcl_GetHashValue(entryPtr)
Tcl_SetHashValue(entryPtr, value)
char *
Tcl_GetHashKey(tablePtr, entryPtr)
Tcl_HashEntry *
Tcl_FirstHashEntry(tablePtr, searchPtr)
Tcl_HashEntry *
Tcl_NextHashEntry(searchPtr)
char *
Tcl_HashStats(tablePtr)
ARGUMENTS
Tcl_HashTable *tablePtr (in) Address of hash table
structure (for all procedures
but Tcl_InitHashTable, this
must have been initialized by
previous call to
Tcl_InitHashTable).
int keyType (in) Kind of keys to use for new
- 1 - Formatted: August 11, 1996
Tcl_Hash(3) Tcl Tcl_Hash(3)
Tcl Library Procedures Tcl Library Procedures
hash table. Must be either
TCL_STRING_KEYS,
TCL_ONE_WORD_KEYS, or an
integer value greater than 1.
char *key (in) Key to use for probe into
table. Exact form depends on
keyType used to create table.
int *newPtr (out) The word at *newPtr is set to
1 if a new entry was created
and 0 if there was already an
entry for key.
Tcl_HashEntry *entryPtr (in) Pointer to hash table entry.
ClientData value (in) New value to assign to hash
table entry. Need not have
type ClientData, but must fit
in same space as ClientData.
Tcl_HashSearch *searchPtr (in) Pointer to record to use to
keep track of progress in
enumerating all the entries in
a hash table.
___________________________________________________________________________
DESCRIPTION
A hash table consists of zero or more entries, each consisting of a
key and a value. Given the key for an entry, the hashing routines can
very quickly locate the entry, and hence its value. There may be at
most one entry in a hash table with a particular key, but many entries
may have the same value. Keys can take one of three forms: strings,
one-word values, or integer arrays. All of the keys in a given table
have the same form, which is specified when the table is initialized.
The value of a hash table entry can be anything that fits in the same
space as a ``char *'' pointer. Values for hash table entries are
managed entirely by clients, not by the hash module itself. Typically
each entry's value is a pointer to a data structure managed by client
code.
Hash tables grow gracefully as the number of entries increases, so
that there are always less than three entries per hash bucket, on
average. This allows for fast lookups regardless of the number of
entries in a table.
Tcl_InitHashTable initializes a structure that describes a new hash
- 2 - Formatted: August 11, 1996
Tcl_Hash(3) Tcl Tcl_Hash(3)
Tcl Library Procedures Tcl Library Procedures
table. The space for the structure is provided by the caller, not by
the hash module. The value of keyType indicates what kinds of keys
will be used for all entries in the table. KeyType must have one of
the following values:
TCL_STRING_KEYS Keys are null-terminated ASCII strings. They
are passed to hashing routines using the
address of the first character of the string.
TCL_ONE_WORD_KEYS Keys are single-word values; they are passed
to hashing routines and stored in hash table
entries as ``char *'' values. The pointer
value is the key; it need not (and usually
doesn't) actually point to a string.
other If keyType is not TCL_STRING_KEYS or
TCL_ONE_WORD_KEYS, then it must be an integer
value greater than 1. In this case the keys
will be arrays of ``int'' values, where
keyType gives the number of ints in each key.
This allows structures to be used as keys.
All keys must have the same size. Array keys
are passed into hashing functions using the
address of the first int in the array.
Tcl_DeleteHashTable deletes all of the entries in a hash table and
frees up the memory associated with the table's bucket array and
entries. It does not free the actual table structure (pointed to by
tablePtr), since that memory is assumed to be managed by the client.
Tcl_DeleteHashTable also does not free or otherwise manipulate the
values of the hash table entries. If the entry values point to
dynamically-allocated memory, then it is the client's responsibility
to free these structures before deleting the table.
Tcl_CreateHashEntry locates the entry corresponding to a particular
key, creating a new entry in the table if there wasn't already one
with the given key. If an entry already existed with the given key
then *newPtr is set to zero. If a new entry was created, then *newPtr
is set to a non-zero value and the value of the new entry will be set
to zero. The return value from Tcl_CreateHashEntry is a pointer to
the entry, which may be used to retrieve and modify the entry's value
or to delete the entry from the table.
Tcl_DeleteHashEntry will remove an existing entry from a table. The
memory associated with the entry itself will be freed, but the client
is responsible for any cleanup associated with the entry's value, such
as freeing a structure that it points to.
Tcl_FindHashEntry is similar to Tcl_CreateHashEntry except that it
- 3 - Formatted: August 11, 1996
Tcl_Hash(3) Tcl Tcl_Hash(3)
Tcl Library Procedures Tcl Library Procedures
doesn't create a new entry if the key doesn't exist; instead, it
returns NULL as result.
Tcl_GetHashValue and Tcl_SetHashValue are used to read and write an
entry's value, respectively. Values are stored and retrieved as type
``ClientData'', which is large enough to hold a pointer value. On
almost all machines this is large enough to hold an integer value too.
Tcl_GetHashKey returns the key for a given hash table entry, either as
a pointer to a string, a one-word (``char *'') key, or as a pointer to
the first word of an array of integers, depending on the keyType used
to create a hash table. In all cases Tcl_GetHashKey returns a result
with type ``char *''. When the key is a string or array, the result
of Tcl_GetHashKey points to information in the table entry; this
information will remain valid until the entry is deleted or its table
is deleted.
Tcl_FirstHashEntry and Tcl_NextHashEntry may be used to scan all of
the entries in a hash table. A structure of type ``Tcl_HashSearch'',
provided by the client, is used to keep track of progress through the
table. Tcl_FirstHashEntry initializes the search record and returns
the first entry in the table (or NULL if the table is empty). Each
susequent call to Tcl_NextHashEntry returns the next entry in the
table or NULL if the end of the table has been reached. A call to
Tcl_FirstHashEntry followed by calls to Tcl_NextHashEntry will return
each of the entries in the table exactly once, in an arbitrary order.
It is unadvisable to modify the structure of the table, e.g. by
creating or deleting entries, while the search is in progress.
Tcl_HashStats returns a dynamically-allocated string with overall
information about a hash table, such as the number of entries it
contains, the number of buckets in its hash array, and the utilization
of the buckets. It is the caller's responsibility to free the result
string by passing it to free.
The header file tcl.h defines the actual data structures used to
implement hash tables. This is necessary so that clients can allocate
Tcl_HashTable structures and so that macros can be used to read and
write the values of entries. However, users of the hashing routines
should never refer directly to any of the fields of any of the hash-
related data structures; use the procedures and macros defined here.
KEYWORDS
hash table, key, lookup, search, value
- 4 - Formatted: August 11, 1996