1Tcl_Hash(3) Tcl Library Procedures Tcl_Hash(3)
2______________________________________________________________________________
6
8 Tcl_InitHashTable, Tcl_InitCustomHashTable, Tcl_InitObjHashTable,
9 Tcl_DeleteHashTable, Tcl_CreateHashEntry, Tcl_DeleteHashEntry,
10 Tcl_FindHashEntry, Tcl_GetHashValue, Tcl_SetHashValue, Tcl_GetHashKey,
11 Tcl_FirstHashEntry, Tcl_NextHashEntry, Tcl_HashStats - procedures to
12 manage hash tables
13
15 #include <tcl.h>
16 Tcl_InitHashTable(tablePtr, keyType)
18 Tcl_InitCustomHashTable(tablePtr, keyType, typePtr)
20 Tcl_InitObjHashTable(tablePtr)
22 Tcl_DeleteHashTable(tablePtr)
24 Tcl_HashEntry *
26 Tcl_CreateHashEntry(tablePtr, key, newPtr)
27 Tcl_DeleteHashEntry(entryPtr)
29 Tcl_HashEntry *
31 Tcl_FindHashEntry(tablePtr, key)
32 ClientData
34 Tcl_GetHashValue(entryPtr)
35 Tcl_SetHashValue(entryPtr, value)
37 void *
39 Tcl_GetHashKey(tablePtr, entryPtr)
40 Tcl_HashEntry *
42 Tcl_FirstHashEntry(tablePtr, searchPtr)
43 Tcl_HashEntry *
45 Tcl_NextHashEntry(searchPtr)
46 char *
48 Tcl_HashStats(tablePtr)
49
51 Tcl_HashTable *tablePtr (in) Address of hash table
52 structure (for all pro‐
53 cedures but
54 Tcl_InitHashTable, this
55 must have been initial‐
56 ized by previous call to
57 Tcl_InitHashTable).
58 int keyType (in) Kind of keys to use for
60 new hash table. Must be
61 either TCL_STRING_KEYS,
62 TCL_ONE_WORD_KEYS,
63 TCL_CUSTOM_TYPE_KEYS,
64 TCL_CUSTOM_PTR_KEYS, or
65 an integer value greater
66 than 1.
67 Tcl_HashKeyType *typePtr (in) Address of structure
69 which defines the behav‐
70 ior of the hash table.
71 const void *key (in) Key to use for probe
73 into table. Exact form
74 depends on keyType used
75 to create table.
76 int *newPtr (out) The word at *newPtr is
78 set to 1 if a new entry
79 was created and 0 if
80 there was already an
81 entry for key.
82 Tcl_HashEntry *entryPtr (in) Pointer to hash table
84 entry.
85 ClientData value (in) New value to assign to
87 hash table entry. Need
88 not have type Client‐
89 Data, but must fit in
90 same space as Client‐
91 Data.
92 Tcl_HashSearch *searchPtr (in) Pointer to record to use
94 to keep track of
95 progress in enumerating
96 all the entries in a
97 hash table.
98______________________________________________________________________________
99
101 A hash table consists of zero or more entries, each consisting of a key
102 and a value. Given the key for an entry, the hashing routines can very
103 quickly locate the entry, and hence its value. There may be at most one
104 entry in a hash table with a particular key, but many entries may have
105 the same value. Keys can take one of four forms: strings, one-word
106 values, integer arrays, or custom keys defined by a Tcl_HashKeyType
107 structure (See section THE TCL_HASHKEYTYPE STRUCTURE below). All of the
108 keys in a given table have the same form, which is specified when the
109 table is initialized.
110 The value of a hash table entry can be anything that fits in the same
112 space as a “char *” pointer. Values for hash table entries are managed
113 entirely by clients, not by the hash module itself. Typically each
114 entry's value is a pointer to a data structure managed by client code.
115 Hash tables grow gracefully as the number of entries increases, so that
117 there are always less than three entries per hash bucket, on average.
118 This allows for fast lookups regardless of the number of entries in a
119 table.
120 The core provides three functions for the initialization of hash
122 tables, Tcl_InitHashTable, Tcl_InitObjHashTable and Tcl_InitCus‐
123 tomHashTable.
124 Tcl_InitHashTable initializes a structure that describes a new hash ta‐
126 ble. The space for the structure is provided by the caller, not by the
127 hash module. The value of keyType indicates what kinds of keys will be
128 used for all entries in the table. All of the key types described later
129 are allowed, with the exception of TCL_CUSTOM_TYPE_KEYS and TCL_CUS‐
130 TOM_PTR_KEYS.
131 Tcl_InitObjHashTable is a wrapper around Tcl_InitCustomHashTable and
133 initializes a hash table whose keys are Tcl_Obj *.
134 Tcl_InitCustomHashTable initializes a structure that describes a new
136 hash table. The space for the structure is provided by the caller, not
137 by the hash module. The value of keyType indicates what kinds of keys
138 will be used for all entries in the table. KeyType must have one of
139 the following values:
140 TCL_STRING_KEYS Keys are null-terminated strings. They are
142 passed to hashing routines using the address
143 of the first character of the string.
144 TCL_ONE_WORD_KEYS Keys are single-word values; they are passed
146 to hashing routines and stored in hash table
147 entries as “char *” values. The pointer value
148 is the key; it need not (and usually does
149 not) actually point to a string.
150 TCL_CUSTOM_TYPE_KEYS Keys are of arbitrary type, and are stored in
152 the entry. Hashing and comparison is deter‐
153 mined by typePtr. The Tcl_HashKeyType struc‐
154 ture is described in the section THE
155 TCL_HASHKEYTYPE STRUCTURE below.
156 TCL_CUSTOM_PTR_KEYS Keys are pointers to an arbitrary type, and
158 are stored in the entry. Hashing and compari‐
159 son is determined by typePtr. The Tcl_HashKey‐
160 Type structure is described in the section THE
161 TCL_HASHKEYTYPE STRUCTURE below.
162 other If keyType is not one of the above, then it
164 must be an integer value greater than 1. In
165 this case the keys will be arrays of “int”
166 values, where keyType gives the number of ints
167 in each key. This allows structures to be
168 used as keys. All keys must have the same
169 size. Array keys are passed into hashing
170 functions using the address of the first int
171 in the array.
172 Tcl_DeleteHashTable deletes all of the entries in a hash table and
174 frees up the memory associated with the table's bucket array and
175 entries. It does not free the actual table structure (pointed to by
176 tablePtr), since that memory is assumed to be managed by the client.
177 Tcl_DeleteHashTable also does not free or otherwise manipulate the val‐
178 ues of the hash table entries. If the entry values point to dynami‐
179 cally-allocated memory, then it is the client's responsibility to free
180 these structures before deleting the table.
181 Tcl_CreateHashEntry locates the entry corresponding to a particular
183 key, creating a new entry in the table if there was not already one
184 with the given key. If an entry already existed with the given key
185 then *newPtr is set to zero. If a new entry was created, then *newPtr
186 is set to a non-zero value and the value of the new entry will be set
187 to zero. The return value from Tcl_CreateHashEntry is a pointer to the
188 entry, which may be used to retrieve and modify the entry's value or to
189 delete the entry from the table.
190 Tcl_DeleteHashEntry will remove an existing entry from a table. The
192 memory associated with the entry itself will be freed, but the client
193 is responsible for any cleanup associated with the entry's value, such
194 as freeing a structure that it points to.
195 Tcl_FindHashEntry is similar to Tcl_CreateHashEntry except that it does
197 not create a new entry if the key doesn't exist; instead, it returns
198 NULL as result.
199 Tcl_GetHashValue and Tcl_SetHashValue are used to read and write an
201 entry's value, respectively. Values are stored and retrieved as type
202 “ClientData”, which is large enough to hold a pointer value. On almost
203 all machines this is large enough to hold an integer value too.
204 Tcl_GetHashKey returns the key for a given hash table entry, either as
206 a pointer to a string, a one-word (“char *”) key, or as a pointer to
207 the first word of an array of integers, depending on the keyType used
208 to create a hash table. In all cases Tcl_GetHashKey returns a result
209 with type “char *”. When the key is a string or array, the result of
210 Tcl_GetHashKey points to information in the table entry; this informa‐
211 tion will remain valid until the entry is deleted or its table is
212 deleted.
213 Tcl_FirstHashEntry and Tcl_NextHashEntry may be used to scan all of the
215 entries in a hash table. A structure of type “Tcl_HashSearch”, pro‐
216 vided by the client, is used to keep track of progress through the ta‐
217 ble. Tcl_FirstHashEntry initializes the search record and returns the
218 first entry in the table (or NULL if the table is empty). Each subse‐
219 quent call to Tcl_NextHashEntry returns the next entry in the table or
220 NULL if the end of the table has been reached. A call to
221 Tcl_FirstHashEntry followed by calls to Tcl_NextHashEntry will return
222 each of the entries in the table exactly once, in an arbitrary order.
223 It is inadvisable to modify the structure of the table, e.g. by creat‐
224 ing or deleting entries, while the search is in progress, with the
225 exception of deleting the entry returned by Tcl_FirstHashEntry or
226 Tcl_NextHashEntry.
227 Tcl_HashStats returns a dynamically-allocated string with overall
229 information about a hash table, such as the number of entries it con‐
230 tains, the number of buckets in its hash array, and the utilization of
231 the buckets. It is the caller's responsibility to free the result
232 string by passing it to ckfree.
233 The header file tcl.h defines the actual data structures used to imple‐
235 ment hash tables. This is necessary so that clients can allocate
236 Tcl_HashTable structures and so that macros can be used to read and
237 write the values of entries. However, users of the hashing routines
238 should never refer directly to any of the fields of any of the hash-
239 related data structures; use the procedures and macros defined here.
240
242 Extension writers can define new hash key types by defining four proce‐
243 dures, initializing a Tcl_HashKeyType structure to describe the type,
244 and calling Tcl_InitCustomHashTable. The Tcl_HashKeyType structure is
245 defined as follows:
246 typedef struct Tcl_HashKeyType {
248 int version;
249 int flags;
250 Tcl_HashKeyProc *hashKeyProc;
251 Tcl_CompareHashKeysProc *compareKeysProc;
252 Tcl_AllocHashEntryProc *allocEntryProc;
253 Tcl_FreeHashEntryProc *freeEntryProc;
254 } Tcl_HashKeyType;
255 The version member is the version of the table. If this structure is
257 extended in future then the version can be used to distinguish between
258 different structures. It should be set to TCL_HASH_KEY_TYPE_VERSION.
259 The flags member is 0 or one or more of the following values OR'ed
261 together:
262 TCL_HASH_KEY_RANDOMIZE_HASH
264 There are some things, pointers for example
265 which do not hash well because they do not use
266 the lower bits. If this flag is set then the
267 hash table will attempt to rectify this by
268 randomizing the bits and then using the upper
269 N bits as the index into the table.
270 TCL_HASH_KEY_SYSTEM_HASH This flag forces Tcl to use the memory alloca‐
272 tion procedures provided by the operating sys‐
273 tem when allocating and freeing memory used to
274 store the hash table data structures, and not
275 any of Tcl's own customized memory allocation
276 routines. This is important if the hash table
277 is to be used in the implementation of a cus‐
278 tom set of allocation routines, or something
279 that a custom set of allocation routines might
280 depend on, in order to avoid any circular
281 dependency.
282 The hashKeyProc member contains the address of a function called to
284 calculate a hash value for the key.
285 typedef unsigned int Tcl_HashKeyProc(
287 Tcl_HashTable *tablePtr,
288 void *keyPtr);
289 If this is NULL then keyPtr is used and TCL_HASH_KEY_RANDOMIZE_HASH is
291 assumed.
292 The compareKeysProc member contains the address of a function called to
294 compare two keys.
295 typedef int Tcl_CompareHashKeysProc(
297 void *keyPtr,
298 Tcl_HashEntry *hPtr);
299 If this is NULL then the keyPtr pointers are compared. If the keys do
301 not match then the function returns 0, otherwise it returns 1.
302 The allocEntryProc member contains the address of a function called to
304 allocate space for an entry and initialize the key and clientData.
305 typedef Tcl_HashEntry *Tcl_AllocHashEntryProc(
307 Tcl_HashTable *tablePtr,
308 void *keyPtr);
309 If this is NULL then Tcl_Alloc is used to allocate enough space for a
311 Tcl_HashEntry, the key pointer is assigned to key.oneWordValue and the
312 clientData is set to NULL. String keys and array keys use this function
313 to allocate enough space for the entry and the key in one block, rather
314 than doing it in two blocks. This saves space for a pointer to the key
315 from the entry and another memory allocation. Tcl_Obj* keys use this
316 function to allocate enough space for an entry and increment the refer‐
317 ence count on the value.
318 The freeEntryProc member contains the address of a function called to
320 free space for an entry.
321 typedef void Tcl_FreeHashEntryProc(
323 Tcl_HashEntry *hPtr);
324 If this is NULL then Tcl_Free is used to free the space for the entry.
326 Tcl_Obj* keys use this function to decrement the reference count on the
327 value.
328
330 hash table, key, lookup, search, value
331Tcl Tcl_Hash(3)