Cursor

Cursors are used to navigate sets of records returned by index searches with functions mco_cursor_first(), mco_cursor_last(), mco_cursor_prev() and mco_cursor_next(). A cursor structure is also used for calls to generated index_cursor functions and mco_uda_cursor() Following is the definition of the mco_cursor_t structure as defined in mco.h:

 
 
    #define mco_cursor_size      (100*sizeof(mco_offs_t))   /* cursor structure size */
     
    typedef struct mco_cursor_t_
    {
        MCO_PUB_STRUCT_BASE c[mco_cursor_size_w];
     
    } mco_cursor_t,  /* cursor (structure)            */
    *mco_cursor_h; /* cursor handle (pointer)       */
 

The array c contains 100 offsets values. These are set to the addresses of database records satisfying a search.

Cursor Types

Cursors are of different types depending on the type of index they operate on. The following cursor types are defined in mco.h:

 
    typedef enum MCO_CURSOR_TYPE_E_
    {
        MCO_LIST_CURSOR = 0, MCO_TREE_CURSOR = 1, 
        MCO_HASH_CURSOR = 2, MCO_KDTREE_CURSOR = 3, 
        MCO_PTREE_CURSOR = 4, MCO_RTREE_CURSOR = 5
     
    } MCO_CURSOR_TYPE;
     

 

MCO_LIST_CURSOR	List (hash) index cursor.
MCO_TREE_CURSOR	tree index cursor
MCO_HASH_CURSOR	hash index cursor
MCO_KDTREE_CURSOR	kdtree index cursor
MCO_PTREE_CURSOR	patricia Trie index cursor
MCO_RTREE_CURSOR	rtree index cursor

 

Cursor Operation Codes

When calling an index search function to return a cursor, one of the following cursor operator codes (opcodes) must be specified:

 
    typedef enum MCO_OPCODE_E_
    {
        MCO_NOP = 0,  /* No operation */
        MCO_LT = 1,   /* Values less-than sample */
        MCO_LE = 2,   /* Values less-or-equal to the sample */
        MCO_EQ = 3,   /* Values equal to the sample */
        MCO_GE = 4,   /* Values greater-or-equal to the sample */
        MCO_GT = 5,   /* Values greater-than the sample */
        MCO_OVERLAP = 6,  /* rtree, overlapping regions */
        MCO_CONTAIN = 7,  /* rtree, containing regions */
        MCO_EX = 8,       /* patricia, exact match */
        MCO_BEST = 9,     /* patricia, the best, longest match */
        MCO_PREF = 10,    /* patricia, prefix match */
        MCO_NEXT_MATCH = 11, /* patricia, continue search instead of new search */
        MCO_NEIGHBOURHOOD = 12, /* rtree, list object distances from the sample */
        MCO_NEIGHBORHOOD = MCO_NEIGHBOURHOOD, /* American synonym */
        MCO_BELONG = MCO_LE /* patricia, sample belongs to value */
     
    } MCO_OPCODE;
     

 

MCO_NOP	No Operation
MCO_LT	Values less-than sample
MCO_LE	Values less-or-equal to the sample
MCO_EQ	Values equal to the sample
MCO_GE	Values greater-than-or-equal-to the sample
MCO_GT	Values greater-than the sample
MCO_OVERLAP	rtree, overlapping regions
MCO_CONTAIN	rtree, containing regions
MCO_EX	patricia, exact match
MCO_BEST	patricia, the best, longest match
MCO_PREF	patricia, prefix match
MCO_NEXT_MATCH	patricia, continue search instead of new search
MCO_NEIGHBORHOOD (= MCO_NEIGHBOURHOOD)	rtree, list object distances from the sample
MCO_BELONG (= MCO_LE)	patricia, sample belongs to value