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| 244 | \\$1\l'|0\(ul'\\$2 |
| 245 | .. |
| 246 | .TH Tcl_Hash 3 "" Tcl "Tcl Library Procedures" |
| 247 | .BS |
| 248 | .SH NAME |
| 249 | Tcl_InitHashTable, Tcl_InitCustomHashTable, Tcl_InitObjHashTable, 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 |
| 250 | .SH SYNOPSIS |
| 251 | .nf |
| 252 | \fB#include <tcl.h>\fR |
| 253 | .sp |
| 254 | \fBTcl_InitHashTable\fR(\fItablePtr, keyType\fR) |
| 255 | .sp |
| 256 | \fBTcl_InitCustomHashTable\fR(\fItablePtr, keyType, typePtr\fR) |
| 257 | .sp |
| 258 | \fBTcl_InitObjHashTable\fR(\fItablePtr\fR) |
| 259 | .sp |
| 260 | \fBTcl_DeleteHashTable\fR(\fItablePtr\fR) |
| 261 | .sp |
| 262 | Tcl_HashEntry * |
| 263 | \fBTcl_CreateHashEntry\fR(\fItablePtr, key, newPtr\fR) |
| 264 | .sp |
| 265 | \fBTcl_DeleteHashEntry\fR(\fIentryPtr\fR) |
| 266 | .sp |
| 267 | Tcl_HashEntry * |
| 268 | \fBTcl_FindHashEntry\fR(\fItablePtr, key\fR) |
| 269 | .sp |
| 270 | ClientData |
| 271 | \fBTcl_GetHashValue\fR(\fIentryPtr\fR) |
| 272 | .sp |
| 273 | \fBTcl_SetHashValue\fR(\fIentryPtr, value\fR) |
| 274 | .sp |
| 275 | char * |
| 276 | \fBTcl_GetHashKey\fR(\fItablePtr, entryPtr\fR) |
| 277 | .sp |
| 278 | Tcl_HashEntry * |
| 279 | \fBTcl_FirstHashEntry\fR(\fItablePtr, searchPtr\fR) |
| 280 | .sp |
| 281 | Tcl_HashEntry * |
| 282 | \fBTcl_NextHashEntry\fR(\fIsearchPtr\fR) |
| 283 | .sp |
| 284 | CONST char * |
| 285 | \fBTcl_HashStats\fR(\fItablePtr\fR) |
| 286 | .SH ARGUMENTS |
| 287 | .AS Tcl_HashSearch *searchPtr |
| 288 | .AP Tcl_HashTable *tablePtr in |
| 289 | Address of hash table structure (for all procedures but |
| 290 | \fBTcl_InitHashTable\fR, this must have been initialized by |
| 291 | previous call to \fBTcl_InitHashTable\fR). |
| 292 | .AP int keyType in |
| 293 | Kind of keys to use for new hash table. Must be either |
| 294 | TCL_STRING_KEYS, TCL_ONE_WORD_KEYS, TCL_CUSTOM_TYPE_KEYS, |
| 295 | TCL_CUSTOM_PTR_KEYS, or an integer value greater than 1. |
| 296 | .AP Tcl_HashKeyType *typePtr in |
| 297 | Address of structure which defines the behaviour of the hash table. |
| 298 | .AP "CONST char" *key in |
| 299 | Key to use for probe into table. Exact form depends on |
| 300 | \fIkeyType\fR used to create table. |
| 301 | .AP int *newPtr out |
| 302 | The word at \fI*newPtr\fR is set to 1 if a new entry was created |
| 303 | and 0 if there was already an entry for \fIkey\fR. |
| 304 | .AP Tcl_HashEntry *entryPtr in |
| 305 | Pointer to hash table entry. |
| 306 | .AP ClientData value in |
| 307 | New value to assign to hash table entry. Need not have type |
| 308 | ClientData, but must fit in same space as ClientData. |
| 309 | .AP Tcl_HashSearch *searchPtr in |
| 310 | Pointer to record to use to keep track of progress in enumerating |
| 311 | all the entries in a hash table. |
| 312 | .BE |
| 313 | .SH DESCRIPTION |
| 314 | .PP |
| 315 | A hash table consists of zero or more entries, each consisting of a |
| 316 | key and a value. Given the key for an entry, the hashing routines can |
| 317 | very quickly locate the entry, and hence its value. There may be at |
| 318 | most one entry in a hash table with a particular key, but many entries |
| 319 | may have the same value. Keys can take one of four forms: strings, |
| 320 | one-word values, integer arrays, or custom keys defined by a |
| 321 | Tcl_HashKeyType structure (See section \fBTHE TCL_HASHKEYTYPE |
| 322 | STRUCTURE\fR below). All of the keys in a given table have the same |
| 323 | form, which is specified when the table is initialized. |
| 324 | .PP |
| 325 | The value of a hash table entry can be anything that fits in the same |
| 326 | space as a ``char *'' pointer. Values for hash table entries are |
| 327 | managed entirely by clients, not by the hash module itself. Typically |
| 328 | each entry's value is a pointer to a data structure managed by client |
| 329 | code. |
| 330 | .PP |
| 331 | Hash tables grow gracefully as the number of entries increases, so |
| 332 | that there are always less than three entries per hash bucket, on |
| 333 | average. This allows for fast lookups regardless of the number of |
| 334 | entries in a table. |
| 335 | .PP |
| 336 | The core provides three functions for the initialization of hash |
| 337 | tables, Tcl_InitHashTable, Tcl_InitObjHashTable and |
| 338 | Tcl_InitCustomHashTable. |
| 339 | .PP |
| 340 | \fBTcl_InitHashTable\fR initializes a structure that describes a new |
| 341 | hash table. The space for the structure is provided by the caller, |
| 342 | not by the hash module. The value of \fIkeyType\fR indicates what |
| 343 | kinds of keys will be used for all entries in the table. All of the |
| 344 | key types described later are allowed, with the exception of |
| 345 | \fBTCL_CUSTOM_TYPE_KEYS\fR and \fBTCL_CUSTOM_PTR_KEYS\fR. |
| 346 | .PP |
| 347 | \fBTcl_InitObjHashTable\fR is a wrapper around |
| 348 | \fBTcl_InitCustomHashTable\fR and initializes a hash table whose keys |
| 349 | are Tcl_Obj *. |
| 350 | .PP |
| 351 | \fBTcl_InitCustomHashTable\fR initializes a structure that describes a |
| 352 | new hash table. The space for the structure is provided by the |
| 353 | caller, not by the hash module. The value of \fIkeyType\fR indicates |
| 354 | what kinds of keys will be used for all entries in the table. |
| 355 | \fIKeyType\fR must have one of the following values: |
| 356 | .IP \fBTCL_STRING_KEYS\fR 25 |
| 357 | Keys are null-terminated strings. |
| 358 | They are passed to hashing routines using the address of the |
| 359 | first character of the string. |
| 360 | .IP \fBTCL_ONE_WORD_KEYS\fR 25 |
| 361 | Keys are single-word values; they are passed to hashing routines |
| 362 | and stored in hash table entries as ``char *'' values. |
| 363 | The pointer value is the key; it need not (and usually doesn't) |
| 364 | actually point to a string. |
| 365 | .IP \fBTCL_CUSTOM_TYPE_KEYS\fR 25 |
| 366 | Keys are of arbitrary type, and are stored in the entry. Hashing |
| 367 | and comparison is determined by \fItypePtr\fR. The Tcl_HashKeyType |
| 368 | structure is described in the section |
| 369 | \fBTHE TCL_HASHKEYTYPE STRUCTURE\fR below. |
| 370 | .IP \fBTCL_CUSTOM_PTR_KEYS\fR 25 |
| 371 | Keys are pointers to an arbitrary type, and are stored in the entry. Hashing |
| 372 | and comparison is determined by \fItypePtr\fR. The Tcl_HashKeyType |
| 373 | structure is described in the section |
| 374 | \fBTHE TCL_HASHKEYTYPE STRUCTURE\fR below. |
| 375 | .IP \fIother\fR 25 |
| 376 | If \fIkeyType\fR is not one of the above, |
| 377 | then it must be an integer value greater than 1. |
| 378 | In this case the keys will be arrays of ``int'' values, where |
| 379 | \fIkeyType\fR gives the number of ints in each key. |
| 380 | This allows structures to be used as keys. |
| 381 | All keys must have the same size. |
| 382 | Array keys are passed into hashing functions using the address |
| 383 | of the first int in the array. |
| 384 | .PP |
| 385 | \fBTcl_DeleteHashTable\fR deletes all of the entries in a hash |
| 386 | table and frees up the memory associated with the table's |
| 387 | bucket array and entries. |
| 388 | It does not free the actual table structure (pointed to |
| 389 | by \fItablePtr\fR), since that memory is assumed to be managed |
| 390 | by the client. |
| 391 | \fBTcl_DeleteHashTable\fR also does not free or otherwise |
| 392 | manipulate the values of the hash table entries. |
| 393 | If the entry values point to dynamically-allocated memory, then |
| 394 | it is the client's responsibility to free these structures |
| 395 | before deleting the table. |
| 396 | .PP |
| 397 | \fBTcl_CreateHashEntry\fR locates the entry corresponding to a |
| 398 | particular key, creating a new entry in the table if there |
| 399 | wasn't already one with the given key. |
| 400 | If an entry already existed with the given key then \fI*newPtr\fR |
| 401 | is set to zero. |
| 402 | If a new entry was created, then \fI*newPtr\fR is set to a non-zero |
| 403 | value and the value of the new entry will be set to zero. |
| 404 | The return value from \fBTcl_CreateHashEntry\fR is a pointer to |
| 405 | the entry, which may be used to retrieve and modify the entry's |
| 406 | value or to delete the entry from the table. |
| 407 | .PP |
| 408 | \fBTcl_DeleteHashEntry\fR will remove an existing entry from a |
| 409 | table. |
| 410 | The memory associated with the entry itself will be freed, but |
| 411 | the client is responsible for any cleanup associated with the |
| 412 | entry's value, such as freeing a structure that it points to. |
| 413 | .PP |
| 414 | \fBTcl_FindHashEntry\fR is similar to \fBTcl_CreateHashEntry\fR |
| 415 | except that it doesn't create a new entry if the key doesn't exist; |
| 416 | instead, it returns NULL as result. |
| 417 | .PP |
| 418 | \fBTcl_GetHashValue\fR and \fBTcl_SetHashValue\fR are used to |
| 419 | read and write an entry's value, respectively. |
| 420 | Values are stored and retrieved as type ``ClientData'', which is |
| 421 | large enough to hold a pointer value. On almost all machines this is |
| 422 | large enough to hold an integer value too. |
| 423 | .PP |
| 424 | \fBTcl_GetHashKey\fR returns the key for a given hash table entry, |
| 425 | either as a pointer to a string, a one-word (``char *'') key, or |
| 426 | as a pointer to the first word of an array of integers, depending |
| 427 | on the \fIkeyType\fR used to create a hash table. |
| 428 | In all cases \fBTcl_GetHashKey\fR returns a result with type |
| 429 | ``char *''. |
| 430 | When the key is a string or array, the result of \fBTcl_GetHashKey\fR |
| 431 | points to information in the table entry; this information will |
| 432 | remain valid until the entry is deleted or its table is deleted. |
| 433 | .PP |
| 434 | \fBTcl_FirstHashEntry\fR and \fBTcl_NextHashEntry\fR may be used |
| 435 | to scan all of the entries in a hash table. |
| 436 | A structure of type ``Tcl_HashSearch'', provided by the client, |
| 437 | is used to keep track of progress through the table. |
| 438 | \fBTcl_FirstHashEntry\fR initializes the search record and |
| 439 | returns the first entry in the table (or NULL if the table is |
| 440 | empty). |
| 441 | Each subsequent call to \fBTcl_NextHashEntry\fR returns the |
| 442 | next entry in the table or |
| 443 | NULL if the end of the table has been reached. |
| 444 | A call to \fBTcl_FirstHashEntry\fR followed by calls to |
| 445 | \fBTcl_NextHashEntry\fR will return each of the entries in |
| 446 | the table exactly once, in an arbitrary order. |
| 447 | It is unadvisable to modify the structure of the table, e.g. |
| 448 | by creating or deleting entries, while the search is in |
| 449 | progress. |
| 450 | .PP |
| 451 | \fBTcl_HashStats\fR returns a dynamically-allocated string with |
| 452 | overall information about a hash table, such as the number of |
| 453 | entries it contains, the number of buckets in its hash array, |
| 454 | and the utilization of the buckets. |
| 455 | It is the caller's responsibility to free the result string |
| 456 | by passing it to \fBckfree\fR. |
| 457 | .PP |
| 458 | The header file \fBtcl.h\fR defines the actual data structures |
| 459 | used to implement hash tables. |
| 460 | This is necessary so that clients can allocate Tcl_HashTable |
| 461 | structures and so that macros can be used to read and write |
| 462 | the values of entries. |
| 463 | However, users of the hashing routines should never refer directly |
| 464 | to any of the fields of any of the hash-related data structures; |
| 465 | use the procedures and macros defined here. |
| 466 | .SH "THE TCL_HASHKEYTYPE STRUCTURE" |
| 467 | .PP |
| 468 | Extension writers can define new hash key types by defining four |
| 469 | procedures, initializing a Tcl_HashKeyType structure to describe |
| 470 | the type, and calling \fBTcl_InitCustomHashTable\fR. |
| 471 | The \fBTcl_HashKeyType\fR structure is defined as follows: |
| 472 | .CS |
| 473 | typedef struct Tcl_HashKeyType { |
| 474 | int \fIversion\fR; |
| 475 | int \fIflags\fR; |
| 476 | Tcl_HashKeyProc *\fIhashKeyProc\fR; |
| 477 | Tcl_CompareHashKeysProc *\fIcompareKeysProc\fR; |
| 478 | Tcl_AllocHashEntryProc *\fIallocEntryProc\fR; |
| 479 | Tcl_FreeHashEntryProc *\fIfreeEntryProc\fR; |
| 480 | } Tcl_HashKeyType; |
| 481 | .CE |
| 482 | .PP |
| 483 | The \fIversion\fR member is the version of the table. If this |
| 484 | structure is extended in future then the version can be used |
| 485 | to distinguish between different structures. It should be set |
| 486 | to \fBTCL_HASH_KEY_TYPE_VERSION\fR. |
| 487 | .PP |
| 488 | The \fIflags\fR member is one or more of the following values OR'ed together: |
| 489 | .IP \fBTCL_HASH_KEY_RANDOMIZE_HASH\fR 25 |
| 490 | There are some things, pointers for example which don't hash well |
| 491 | because they do not use the lower bits. If this flag is set then the |
| 492 | hash table will attempt to rectify this by randomising the bits and |
| 493 | then using the upper N bits as the index into the table. |
| 494 | .PP |
| 495 | The \fIhashKeyProc\fR member contains the address of a function |
| 496 | called to calculate a hash value for the key. |
| 497 | .CS |
| 498 | typedef unsigned int (Tcl_HashKeyProc) ( |
| 499 | Tcl_HashTable *\fItablePtr\fR, |
| 500 | VOID *\fIkeyPtr\fR); |
| 501 | .CE |
| 502 | If this is NULL then \fIkeyPtr\fR is used and |
| 503 | \fBTCL_HASH_KEY_RANDOMIZE_HASH\fR is assumed. |
| 504 | .PP |
| 505 | The \fIcompareKeysProc\fR member contains the address of a function |
| 506 | called to compare two keys. |
| 507 | .CS |
| 508 | typedef int (Tcl_CompareHashKeysProc) (VOID *\fIkeyPtr\fR, |
| 509 | Tcl_HashEntry *\fIhPtr\fR); |
| 510 | .CE |
| 511 | If this is NULL then the \fIkeyPtr\fR pointers are compared. |
| 512 | If the keys don't match then the function returns 0, otherwise |
| 513 | it returns 1. |
| 514 | .PP |
| 515 | The \fIallocEntryProc\fR member contains the address of a function |
| 516 | called to allocate space for an entry and initialise the key. |
| 517 | .CS |
| 518 | typedef Tcl_HashEntry *(Tcl_AllocHashEntryProc) ( |
| 519 | Tcl_HashTable *\fItablePtr\fR, VOID *\fIkeyPtr\fR); |
| 520 | .CE |
| 521 | If this is NULL then Tcl_Alloc is used to allocate enough space for a |
| 522 | Tcl_HashEntry and the key pointer is assigned to key.oneWordValue. |
| 523 | String keys and array keys use this function to allocate enough |
| 524 | space for the entry and the key in one block, rather than doing |
| 525 | it in two blocks. This saves space for a pointer to the key from |
| 526 | the entry and another memory allocation. Tcl_Obj * keys use this |
| 527 | function to allocate enough space for an entry and increment the |
| 528 | reference count on the object. |
| 529 | If |
| 530 | .PP |
| 531 | The \fIfreeEntryProc\fR member contains the address of a function |
| 532 | called to free space for an entry. |
| 533 | .CS |
| 534 | typedef void (Tcl_FreeHashEntryProc) (Tcl_HashEntry *\fIhPtr\fR); |
| 535 | .CE |
| 536 | If this is NULL then Tcl_Free is used to free the space for the |
| 537 | entry. Tcl_Obj * keys use this function to decrement the |
| 538 | reference count on the object. |
| 539 | .SH KEYWORDS |
| 540 | hash table, key, lookup, search, value |