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219 | See the \\fBoptions\\fR manual entry for details on the standard options. | |
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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 |