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 char *
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 struc‐
52 ture (for all procedures but
53 Tcl_InitHashTable, this must
54 have been initialized by pre‐
55 vious call to
56 Tcl_InitHashTable).
57 int keyType (in) Kind of keys to use for new
59 hash table. Must be either
60 TCL_STRING_KEYS,
61 TCL_ONE_WORD_KEYS, TCL_CUS‐
62 TOM_TYPE_KEYS, TCL_CUS‐
63 TOM_PTR_KEYS, or an integer
64 value greater than 1.
65 Tcl_HashKeyType *typePtr (in) Address of structure which
67 defines the behaviour of the
68 hash table.
69 const char *key (in) Key to use for probe into ta‐
71 ble. Exact form depends on
72 keyType used to create table.
73 int *newPtr (out) The word at *newPtr is set to
75 1 if a new entry was created
76 and 0 if there was already an
77 entry for key.
78 Tcl_HashEntry *entryPtr (in) Pointer to hash table entry.
80 ClientData value (in) New value to assign to hash
82 table entry. Need not have
83 type ClientData, but must fit
84 in same space as ClientData.
85 Tcl_HashSearch *searchPtr (in) Pointer to record to use to
87 keep track of progress in enu‐
88 merating all the entries in a
89 hash table.
90_________________________________________________________________
91
93 A hash table consists of zero or more entries, each consisting of a key
94 and a value. Given the key for an entry, the hashing routines can very
95 quickly locate the entry, and hence its value. There may be at most one
96 entry in a hash table with a particular key, but many entries may have
97 the same value. Keys can take one of four forms: strings, one-word
98 values, integer arrays, or custom keys defined by a Tcl_HashKeyType
99 structure (See section THE TCL_HASHKEYTYPE STRUCTURE below). All of the
100 keys in a given table have the same form, which is specified when the
101 table is initialized.
102 The value of a hash table entry can be anything that fits in the same
104 space as a “char *” pointer. Values for hash table entries are managed
105 entirely by clients, not by the hash module itself. Typically each
106 entry's value is a pointer to a data structure managed by client code.
107 Hash tables grow gracefully as the number of entries increases, so that
109 there are always less than three entries per hash bucket, on average.
110 This allows for fast lookups regardless of the number of entries in a
111 table.
112 The core provides three functions for the initialization of hash
114 tables, Tcl_InitHashTable, Tcl_InitObjHashTable and Tcl_InitCus‐
115 tomHashTable.
116 Tcl_InitHashTable initializes a structure that describes a new hash ta‐
118 ble. The space for the structure is provided by the caller, not by the
119 hash module. The value of keyType indicates what kinds of keys will be
120 used for all entries in the table. All of the key types described later
121 are allowed, with the exception of TCL_CUSTOM_TYPE_KEYS and TCL_CUS‐
122 TOM_PTR_KEYS.
123 Tcl_InitObjHashTable is a wrapper around Tcl_InitCustomHashTable and
125 initializes a hash table whose keys are Tcl_Obj *.
126 Tcl_InitCustomHashTable initializes a structure that describes a new
128 hash table. The space for the structure is provided by the caller, not
129 by the hash module. The value of keyType indicates what kinds of keys
130 will be used for all entries in the table. KeyType must have one of
131 the following values:
132 TCL_STRING_KEYS Keys are null-terminated strings. They are
134 passed to hashing routines using the address
135 of the first character of the string.
136 TCL_ONE_WORD_KEYS Keys are single-word values; they are passed
138 to hashing routines and stored in hash table
139 entries as “char *” values. The pointer value
140 is the key; it need not (and usually does
141 not) actually point to a string.
142 TCL_CUSTOM_TYPE_KEYS Keys are of arbitrary type, and are stored in
144 the entry. Hashing and comparison is deter‐
145 mined by typePtr. The Tcl_HashKeyType struc‐
146 ture is described in the section THE
147 TCL_HASHKEYTYPE STRUCTURE below.
148 TCL_CUSTOM_PTR_KEYS Keys are pointers to an arbitrary type, and
150 are stored in the entry. Hashing and compari‐
151 son is determined by typePtr. The Tcl_HashKey‐
152 Type structure is described in the section THE
153 TCL_HASHKEYTYPE STRUCTURE below.
154 other If keyType is not one of the above, then it
156 must be an integer value greater than 1. In
157 this case the keys will be arrays of “int”
158 values, where keyType gives the number of ints
159 in each key. This allows structures to be
160 used as keys. All keys must have the same
161 size. Array keys are passed into hashing
162 functions using the address of the first int
163 in the array.
164 Tcl_DeleteHashTable deletes all of the entries in a hash table and
166 frees up the memory associated with the table's bucket array and
167 entries. It does not free the actual table structure (pointed to by
168 tablePtr), since that memory is assumed to be managed by the client.
169 Tcl_DeleteHashTable also does not free or otherwise manipulate the val‐
170 ues of the hash table entries. If the entry values point to dynami‐
171 cally-allocated memory, then it is the client's responsibility to free
172 these structures before deleting the table.
173 Tcl_CreateHashEntry locates the entry corresponding to a particular
175 key, creating a new entry in the table if there was not already one
176 with the given key. If an entry already existed with the given key
177 then *newPtr is set to zero. If a new entry was created, then *newPtr
178 is set to a non-zero value and the value of the new entry will be set
179 to zero. The return value from Tcl_CreateHashEntry is a pointer to the
180 entry, which may be used to retrieve and modify the entry's value or to
181 delete the entry from the table.
182 Tcl_DeleteHashEntry will remove an existing entry from a table. The
184 memory associated with the entry itself will be freed, but the client
185 is responsible for any cleanup associated with the entry's value, such
186 as freeing a structure that it points to.
187 Tcl_FindHashEntry is similar to Tcl_CreateHashEntry except that it does
189 not create a new entry if the key doesn't exist; instead, it returns
190 NULL as result.
191 Tcl_GetHashValue and Tcl_SetHashValue are used to read and write an
193 entry's value, respectively. Values are stored and retrieved as type
194 “ClientData”, which is large enough to hold a pointer value. On almost
195 all machines this is large enough to hold an integer value too.
196 Tcl_GetHashKey returns the key for a given hash table entry, either as
198 a pointer to a string, a one-word (“char *”) key, or as a pointer to
199 the first word of an array of integers, depending on the keyType used
200 to create a hash table. In all cases Tcl_GetHashKey returns a result
201 with type “char *”. When the key is a string or array, the result of
202 Tcl_GetHashKey points to information in the table entry; this informa‐
203 tion will remain valid until the entry is deleted or its table is
204 deleted.
205 Tcl_FirstHashEntry and Tcl_NextHashEntry may be used to scan all of the
207 entries in a hash table. A structure of type “Tcl_HashSearch”, pro‐
208 vided by the client, is used to keep track of progress through the ta‐
209 ble. Tcl_FirstHashEntry initializes the search record and returns the
210 first entry in the table (or NULL if the table is empty). Each subse‐
211 quent call to Tcl_NextHashEntry returns the next entry in the table or
212 NULL if the end of the table has been reached. A call to
213 Tcl_FirstHashEntry followed by calls to Tcl_NextHashEntry will return
214 each of the entries in the table exactly once, in an arbitrary order.
215 It is inadvisable to modify the structure of the table, e.g. by creat‐
216 ing or deleting entries, while the search is in progress, with the
217 exception of deleting the entry returned by Tcl_FirstHashEntry or
218 Tcl_NextHashEntry.
219 Tcl_HashStats returns a dynamically-allocated string with overall
221 information about a hash table, such as the number of entries it con‐
222 tains, the number of buckets in its hash array, and the utilization of
223 the buckets. It is the caller's responsibility to free the result
224 string by passing it to ckfree.
225 The header file tcl.h defines the actual data structures used to imple‐
227 ment hash tables. This is necessary so that clients can allocate
228 Tcl_HashTable structures and so that macros can be used to read and
229 write the values of entries. However, users of the hashing routines
230 should never refer directly to any of the fields of any of the hash-
231 related data structures; use the procedures and macros defined here.
232
234 Extension writers can define new hash key types by defining four proce‐
235 dures, initializing a Tcl_HashKeyType structure to describe the type,
236 and calling Tcl_InitCustomHashTable. The Tcl_HashKeyType structure is
237 defined as follows:
238 typedef struct Tcl_HashKeyType {
239 int version;
240 int flags;
241 Tcl_HashKeyProc *hashKeyProc;
242 Tcl_CompareHashKeysProc *compareKeysProc;
243 Tcl_AllocHashEntryProc *allocEntryProc;
244 Tcl_FreeHashEntryProc *freeEntryProc;
245 } Tcl_HashKeyType;
246 The version member is the version of the table. If this structure is
248 extended in future then the version can be used to distinguish between
249 different structures. It should be set to TCL_HASH_KEY_TYPE_VERSION.
250 The flags member is 0 or one or more of the following values OR'ed
252 together:
253 TCL_HASH_KEY_RANDOMIZE_HASH
255 There are some things, pointers for example
256 which do not hash well because they do not use
257 the lower bits. If this flag is set then the
258 hash table will attempt to rectify this by
259 randomizing the bits and then using the upper
260 N bits as the index into the table.
261 TCL_HASH_KEY_SYSTEM_HASH This flag forces Tcl to use the memory alloca‐ │
263 tion procedures provided by the operating sys‐ │
264 tem when allocating and freeing memory used to │
265 store the hash table data structures, and not │
266 any of Tcl's own customized memory allocation │
267 routines. This is important if the hash table │
268 is to be used in the implementation of a cus‐ │
269 tom set of allocation routines, or something │
270 that a custom set of allocation routines might │
271 depend on, in order to avoid any circular │
272 dependency.
273 The hashKeyProc member contains the address of a function called to
275 calculate a hash value for the key.
276 typedef unsigned int (Tcl_HashKeyProc) (
277 Tcl_HashTable *tablePtr,
278 void *keyPtr);
279 If this is NULL then keyPtr is used and TCL_HASH_KEY_RANDOMIZE_HASH is
280 assumed.
281 The compareKeysProc member contains the address of a function called to
283 compare two keys.
284 typedef int (Tcl_CompareHashKeysProc) (
285 void *keyPtr,
286 Tcl_HashEntry *hPtr);
287 If this is NULL then the keyPtr pointers are compared. If the keys do
288 not match then the function returns 0, otherwise it returns 1.
289 The allocEntryProc member contains the address of a function called to
291 allocate space for an entry and initialize the key and clientData.
292 typedef Tcl_HashEntry *(Tcl_AllocHashEntryProc) (
293 Tcl_HashTable *tablePtr,
294 void *keyPtr);
295 If this is NULL then Tcl_Alloc is used to allocate enough space for a
296 Tcl_HashEntry, the key pointer is assigned to key.oneWordValue and the
297 clientData is set to NULL. String keys and array keys use this function
298 to allocate enough space for the entry and the key in one block, rather
299 than doing it in two blocks. This saves space for a pointer to the key
300 from the entry and another memory allocation. Tcl_Obj* keys use this
301 function to allocate enough space for an entry and increment the refer‐
302 ence count on the object.
303 The freeEntryProc member contains the address of a function called to
305 free space for an entry.
306 typedef void (Tcl_FreeHashEntryProc) (Tcl_HashEntry *hPtr);
307 If this is NULL then Tcl_Free is used to free the space for the entry.
308 Tcl_Obj* keys use this function to decrement the reference count on the
309 object.
310
312 hash table, key, lookup, search, value
313Tcl Tcl_Hash(3)