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recno(3)                 BSD Library Functions Manual                 recno(3)


     recno -- record number database access method


     #include <sys/types.h>
     #include <db.h>


     The routine dbopen() is the library interface to database files.  One of
     the supported file formats is record number files.  The general descrip-
     tion of the database access methods is in dbopen(3), this manual page
     describes only the recno specific information.

     The record number data structure is either variable or fixed-length
     records stored in a flat-file format, accessed by the logical record num-
     ber.  The existence of record number five implies the existence of
     records one through four, and the deletion of record number one causes
     record number five to be renumbered to record number four, as well as the
     cursor, if positioned after record number one, to shift down one record.

     The recno access method specific data structure provided to dbopen() is
     defined in the <db.h> include file as follows:

     typedef struct {
             u_long flags;
             u_int cachesize;
             u_int psize;
             int lorder;
             size_t reclen;
             u_char bval;
             char *bfname;

     The elements of this structure are defined as follows:

     flags   The flag value is specified by or'ing any of the following val-

                     The records are fixed-length, not byte delimited.  The
                     structure element reclen specifies the length of the
                     record, and the structure element bval is used as the pad
                     character.  Any records, inserted into the database, that
                     are less than reclen bytes long are automatically padded.

                     In the interface specified by dbopen(), the sequential
                     record retrieval fills in both the caller's key and data
                     structures.  If the R_NOKEY flag is specified, the cursor
                     routines are not required to fill in the key structure.
                     This permits applications to retrieve records at the end
                     of files without reading all of the intervening records.

                     This flag requires that a snapshot of the file be taken
                     when dbopen() is called, instead of permitting any unmod-
                     ified records to be read from the original file.

             A suggested maximum size, in bytes, of the memory cache.  This
             value is only advisory, and the access method will allocate more
             memory rather than fail.  If cachesize is 0 (no size is speci-
             fied) a default cache is used.

     psize   The recno access method stores the in-memory copies of its
             records in a btree.  This value is the size (in bytes) of the
             pages used for nodes in that tree.  If psize is 0 (no page size
             is specified) a page size is chosen based on the underlying file
             system I/O block size.  See btree(3) for more information.

     lorder  The byte order for integers in the stored database metadata.  The
             number should represent the order as an integer; for example, big
             endian order would be the number 4,321.  If lorder is 0 (no order
             is specified) the current host order is used.

     reclen  The length of a fixed-length record.

     bval    The delimiting byte to be used to mark the end of a record for
             variable-length records, and the pad character for fixed-length
             records.  If no value is specified, newlines (``\n'') are used to
             mark the end of variable-length records and fixed-length records
             are padded with spaces.

     bfname  The recno access method stores the in-memory copies of its
             records in a btree.  If bfname is non-NULL, it specifies the name
             of the btree file, as if specified as the file name for a
             dbopen() of a btree file.

     The data part of the key/data pair used by the recno access method is the
     same as other access methods.  The key is different.  The data field of
     the key should be a pointer to a memory location of type recno_t, as
     defined in the <db.h> include file.  This type is normally the largest
     unsigned integral type available to the implementation.  The size field
     of the key should be the size of that type.

     Because there can be no meta-data associated with the underlying recno
     access method files, any changes made to the default values (e.g. fixed
     record length or byte separator value) must be explicitly specified each
     time the file is opened.

     In the interface specified by dbopen(), using the put interface to create
     a new record will cause the creation of multiple, empty records if the
     record number is more than one greater than the largest record currently
     in the database.


     The recno access method routines may fail and set errno for any of the
     errors specified for the library routine dbopen(3) or the following:

     [EINVAL]           An attempt was made to add a record to a fixed-length
                        database that was too large to fit.


     btree(3), dbopen(3), hash(3), mpool(3)

     Michael Stonebraker, Heidi Stettner, Joseph Kalash, Antonin Guttman, and
     Nadene Lynn, Document Processing in a Relational Database System,
     Memorandum No. UCB/ERL M82/32, May 1982.


     Only big and little endian byte order is supported.

BSD                             August 18, 1994                            BSD

Mac OS X 10.8 - Generated Thu Aug 30 11:00:59 CDT 2012
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