Страницы справочника OS X

Эта страница руководства является частью версии 5.0 Инструментов XCode

Читать страницы руководства

RECNO(3)                 BSD Library Functions Manual                 RECNO(3)

NAME
     recno -- record number database access method

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

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

     The record number data structure is either variable or fixed-length records stored in a flat-file for-mat, format,
     mat, accessed by the logical record number.  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;
     } RECNOINFO;

     The elements of this structure are defined as follows:

     flags   The flag value is specified by or'ing any of the following values:

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

             R_NOKEY
                     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.

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

     cachesize
             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) specified)
             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 speci-fied specified
     fied 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.

ERRORS
     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.

SEE ALSO
     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.

BUGS
     Only big and little endian byte order is supported.

BSD                             August 18, 1994                            BSD