sqlite3/hash.h

   1 /*
   2 ** 2001 September 22
   3 **
   4 ** The author disclaims copyright to this source code.  In place of
   5 ** a legal notice, here is a blessing:
   6 **
   7 **    May you do good and not evil.
   8 **    May you find forgiveness for yourself and forgive others.
   9 **    May you share freely, never taking more than you give.
  10 **
  11 *************************************************************************
  12 ** This is the header file for the generic hash-table implemenation
  13 ** used in SQLite.
  14 **
  15 ** $Id$
  16 */
  17 #ifndef _SQLITE_HASH_H_
  18 #define _SQLITE_HASH_H_
  19
  20 /* Forward declarations of structures. */
  21 typedef struct Hash Hash;
  22 typedef struct HashElem HashElem;
  23
  24 /* A complete hash table is an instance of the following structure.
  25 ** The internals of this structure are intended to be opaque -- client
  26 ** code should not attempt to access or modify the fields of this structure
  27 ** directly.  Change this structure only by using the routines below.
  28 ** However, many of the "procedures" and "functions" for modifying and
  29 ** accessing this structure are really macros, so we can't really make
  30 ** this structure opaque.
  31 */
  32 struct Hash {
  33   char keyClass;          /* SQLITE_HASH_INT, _POINTER, _STRING, _BINARY */
  34   char copyKey;           /* True if copy of key made on insert */
  35   int count;              /* Number of entries in this table */
  36   HashElem *first;        /* The first element of the array */
  37   int htsize;             /* Number of buckets in the hash table */
  38   struct _ht {            /* the hash table */
  39     int count;               /* Number of entries with this hash */
  40     HashElem *chain;         /* Pointer to first entry with this hash */
  41   } *ht;
  42 };
  43
  44 /* Each element in the hash table is an instance of the following
  45 ** structure.  All elements are stored on a single doubly-linked list.
  46 **
  47 ** Again, this structure is intended to be opaque, but it can't really
  48 ** be opaque because it is used by macros.
  49 */
  50 struct HashElem {
  51   HashElem *next, *prev;   /* Next and previous elements in the table */
  52   void *data;              /* Data associated with this element */
  53   void *pKey; int nKey;    /* Key associated with this element */
  54 };
  55
  56 /*
  57 ** There are 4 different modes of operation for a hash table:
  58 **
  59 **   SQLITE_HASH_INT         nKey is used as the key and pKey is ignored.
  60 **
  61 **   SQLITE_HASH_POINTER     pKey is used as the key and nKey is ignored.
  62 **
  63 **   SQLITE_HASH_STRING      pKey points to a string that is nKey bytes long
  64 **                           (including the null-terminator, if any).  Case
  65 **                           is ignored in comparisons.
  66 **
  67 **   SQLITE_HASH_BINARY      pKey points to binary data nKey bytes long.
  68 **                           memcmp() is used to compare keys.
  69 **
  70 ** A copy of the key is made for SQLITE_HASH_STRING and SQLITE_HASH_BINARY
  71 ** if the copyKey parameter to HashInit is 1.
  72 */
  73 /* #define SQLITE_HASH_INT       1 // NOT USED */
  74 /* #define SQLITE_HASH_POINTER   2 // NOT USED */
  75 #define SQLITE_HASH_STRING    3
  76 #define SQLITE_HASH_BINARY    4
  77
  78 /*
  79 ** Access routines.  To delete, insert a NULL pointer.
  80 */
  81 void sqlite3HashInit(Hash*, int keytype, int copyKey);
  82 void *sqlite3HashInsert(Hash*, const void *pKey, int nKey, void *pData);
  83 void *sqlite3HashFind(const Hash*, const void *pKey, int nKey);
  84 void sqlite3HashClear(Hash*);
  85
  86 /*
  87 ** Macros for looping over all elements of a hash table.  The idiom is
  88 ** like this:
  89 **
  90 **   Hash h;
  91 **   HashElem *p;
  92 **   ...
  93 **   for(p=sqliteHashFirst(&h); p; p=sqliteHashNext(p)){
  94 **     SomeStructure *pData = sqliteHashData(p);
  95 **     // do something with pData
  96 **   }
  97 */
  98 #define sqliteHashFirst(H)  ((H)->first)
  99 #define sqliteHashNext(E)   ((E)->next)
 100 #define sqliteHashData(E)   ((E)->data)
 101 #define sqliteHashKey(E)    ((E)->pKey)
 102 #define sqliteHashKeysize(E) ((E)->nKey)
 103
 104 /*
 105 ** Number of entries in a hash table
 106 */
 107 #define sqliteHashCount(H)  ((H)->count)
 108
 109 #endif /* _SQLITE_HASH_H_ */