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DBOPEN(3)			    Linux Programmer's Manual				DBOPEN(3)

NAME
       dbopen - database access methods

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

       DB *dbopen(const char *file, int flags, int mode, DBTYPE type,
		  const void *openinfo);

DESCRIPTION
       Note  well:  This page documents interfaces provided in glibc up until version 2.1.  Since
       version 2.2, glibc no longer provides these interfaces.	Probably, you are looking for the
       APIs provided by the libdb library instead.

       dbopen()  is  the  library  interface  to  database files.  The supported file formats are
       btree, hashed and UNIX file oriented.  The btree format is a representation of  a  sorted,
       balanced tree structure.  The hashed format is an extensible, dynamic hashing scheme.  The
       flat-file format is a byte stream file with fixed or variable length records.  The formats
       and  file  format  specific information are described in detail in their respective manual
       pages btree(3), hash(3) and recno(3).

       dbopen() opens file for reading and/or writing.	Files never intended to be  preserved  on
       disk may be created by setting the file argument to NULL.

       The  flags  and	mode arguments are as specified to the open(2) routine, however, only the
       O_CREAT, O_EXCL, O_EXLOCK, O_NONBLOCK, O_RDONLY, O_RDWR, O_SHLOCK, and O_TRUNC  flags  are
       meaningful.  (Note, opening a database file O_WRONLY is not possible.)

       The type argument is of type DBTYPE (as defined in the <db.h> include file) and may be set
       to DB_BTREE, DB_HASH, or DB_RECNO.

       The openinfo argument is a pointer to an access method specific structure described in the
       access  method's  manual  page.	If openinfo is NULL, each access method will use defaults
       appropriate for the system and the access method.

       dbopen() returns a pointer to a DB structure on success and NULL on error.  The DB  struc-
       ture is defined in the <db.h> include file, and contains at least the following fields:

	   typedef struct {
	       DBTYPE type;
	       int (*close)(const DB *db);
	       int (*del)(const DB *db, const DBT *key, unsigned int flags);
	       int (*fd)(const DB *db);
	       int (*get)(const DB *db, DBT *key, DBT *data,
			  unsigned int flags);
	       int (*put)(const DB *db, DBT *key, const DBT *data,
			  unsigned int flags);
	       int (*sync)(const DB *db, unsigned int flags);
	       int (*seq)(const DB *db, DBT *key, DBT *data,
			  unsigned int flags);
	   } DB;

       These elements describe a database type and a set of functions performing various actions.
       These functions take a pointer to a structure as returned by dbopen(), and  sometimes  one
       or more pointers to key/data structures and a flag value.

       type   The type of the underlying access method (and file format).

       close  A  pointer to a routine to flush any cached information to disk, free any allocated
	      resources, and close the underlying file(s).  Since key/data pairs may be cached in
	      memory, failing to sync the file with a close or sync function may result in incon-
	      sistent or lost information.  close routines return -1 on error (setting errno) and
	      0 on success.

       del    A pointer to a routine to remove key/data pairs from the database.

	      The argument flag may be set to the following value:

	      R_CURSOR
		     Delete the record referenced by the cursor.  The cursor must have previously
		     been initialized.

	      delete routines return -1 on error (setting errno), 0 on	success,  and  1  if  the
	      specified key was not in the file.

       fd     A pointer to a routine which returns a file descriptor representative of the under-
	      lying database.  A file descriptor referencing the same file will  be  returned  to
	      all  processes  which  call dbopen() with the same file name.  This file descriptor
	      may be safely used as an argument to the fcntl(2) and flock(2)  locking  functions.
	      The  file descriptor is not necessarily associated with any of the underlying files
	      used by the access method.  No file descriptor is available  for	in  memory  data-
	      bases.   fd routines return -1 on error (setting errno), and the file descriptor on
	      success.

       get    A pointer to a routine which is the interface for keyed retrieval  from  the  data-
	      base.   The  address  and  length of the data associated with the specified key are
	      returned in the structure referenced by data.  get  routines  return  -1	on  error
	      (setting errno), 0 on success, and 1 if the key was not in the file.

       put    A pointer to a routine to store key/data pairs in the database.

	      The argument flag may be set to one of the following values:

	      R_CURSOR
		     Replace  the  key/data  pair referenced by the cursor.  The cursor must have
		     previously been initialized.

	      R_IAFTER
		     Append the data immediately after the data referenced by key, creating a new
		     key/data  pair.  The record number of the appended key/data pair is returned
		     in the key structure.  (Applicable only to the DB_RECNO access method.)

	      R_IBEFORE
		     Insert the data immediately before the data referenced by	key,  creating	a
		     new  key/data  pair.   The  record  number  of the inserted key/data pair is
		     returned in the key structure.  (Applicable  only	to  the  DB_RECNO  access
		     method.)

	      R_NOOVERWRITE
		     Enter the new key/data pair only if the key does not previously exist.

	      R_SETCURSOR
		     Store  the key/data pair, setting or initializing the position of the cursor
		     to reference it.  (Applicable only to the DB_BTREE and DB_RECNO access meth-
		     ods.)

	      R_SETCURSOR  is available only for the DB_BTREE and DB_RECNO access methods because
	      it implies that the keys have an inherent order which does not change.

	      R_IAFTER and R_IBEFORE are available only for the DB_RECNO  access  method  because
	      they  each  imply  that the access method is able to create new keys.  This is true
	      only if the keys are ordered and independent, record numbers for example.

	      The default behavior of the put routines is to enter the new key/data pair, replac-
	      ing any previously existing key.

	      put  routines  return  -1  on  error  (setting  errno),  0 on success, and 1 if the
	      R_NOOVERWRITE flag was set and the key already exists in the file.

       seq    A pointer to a routine which is the interface for  sequential  retrieval	from  the
	      database.   The  address and length of the key are returned in the structure refer-
	      enced by key, and the address and length of the data are returned in the	structure
	      referenced by data.

	      Sequential  key/data  pair retrieval may begin at any time, and the position of the
	      "cursor" is not affected by calls to the del, get, put, or sync routines.   Modifi-
	      cations  to  the	database  during a sequential scan will be reflected in the scan,
	      that is, records inserted behind the cursor will	not  be  returned  while  records
	      inserted in front of the cursor will be returned.

	      The flag value must be set to one of the following values:

	      R_CURSOR
		     The  data	associated with the specified key is returned.	This differs from
		     the get routines in that it sets or initializes the cursor to  the  location
		     of the key as well.  (Note, for the DB_BTREE access method, the returned key
		     is not necessarily an exact match for the specified key.  The  returned  key
		     is  the  smallest key greater than or equal to the specified key, permitting
		     partial key matches and range searches.)

	      R_FIRST
		     The first key/data pair of the database is returned, and the cursor  is  set
		     or initialized to reference it.

	      R_LAST The last key/data pair of the database is returned, and the cursor is set or
		     initialized to reference it.  (Applicable only to the DB_BTREE and  DB_RECNO
		     access methods.)

	      R_NEXT Retrieve  the  key/data pair immediately after the cursor.  If the cursor is
		     not yet set, this is the same as the R_FIRST flag.

	      R_PREV Retrieve the key/data pair immediately before the cursor.	If the cursor  is
		     not  yet  set, this is the same as the R_LAST flag.  (Applicable only to the
		     DB_BTREE and DB_RECNO access methods.)

	      R_LAST and R_PREV are available only for the DB_BTREE and DB_RECNO  access  methods
	      because they each imply that the keys have an inherent order which does not change.

	      seq routines return -1 on error (setting errno), 0 on success and 1 if there are no
	      key/data pairs less than or greater than the specified  or  current  key.   If  the
	      DB_RECNO	access method is being used, and if the database file is a character spe-
	      cial file and no complete key/data pairs are currently available, the seq  routines
	      return 2.

       sync   A pointer to a routine to flush any cached information to disk.  If the database is
	      in memory only, the sync routine has no effect and will always succeed.

	      The flag value may be set to the following value:

	      R_RECNOSYNC
		     If the DB_RECNO access method is being used, this flag causes the sync  rou-
		     tine  to  apply  to  the  btree file which underlies the recno file, not the
		     recno file itself.  (See the bfname field of the recno(3)	manual	page  for
		     more information.)

	      sync routines return -1 on error (setting errno) and 0 on success.

   Key/data pairs
       Access  to  all file types is based on key/data pairs.  Both keys and data are represented
       by the following data structure:

	   typedef struct {
	       void  *data;
	       size_t size;
	   } DBT;

       The elements of the DBT structure are defined as follows:

       data   A pointer to a byte string.

       size   The length of the byte string.

       Key and data byte strings may reference strings of essentially unlimited  length  although
       any  two of them must fit into available memory at the same time.  It should be noted that
       the access methods provide no guarantees about byte string alignment.

ERRORS
       The dbopen() routine may fail and set errno for	any  of  the  errors  specified  for  the
       library routines open(2) and malloc(3) or the following:

       EFTYPE A file is incorrectly formatted.

       EINVAL A parameter has been specified (hash function, pad byte, etc.) that is incompatible
	      with the current file specification or which is not  meaningful  for  the  function
	      (for  example,  use  of the cursor without prior initialization) or there is a mis-
	      match between the version number of file and the software.

       The close routines may fail and set errno for any of the errors specified for the  library
       routines close(2), read(2), write(2), free(3), or fsync(2).

       The  del, get, put and seq routines may fail and set errno for any of the errors specified
       for the library routines read(2), write(2), free(3) or malloc(3).

       The fd routines will fail and set errno to ENOENT for in memory databases.

       The sync routines may fail and set errno for any of the errors specified for  the  library
       routine fsync(2).

BUGS
       The  typedef  DBT  is  a mnemonic for "data base thang", and was used because no-one could
       think of a reasonable name that wasn't already used.

       The file descriptor interface is a kludge and will be deleted in a future version  of  the
       interface.

       None  of  the  access  methods provide any form of concurrent access, locking, or transac-
       tions.

SEE ALSO
       btree(3), hash(3), mpool(3), recno(3)

       LIBTP: Portable, Modular Transactions for UNIX, Margo Seltzer, Michael Olson, USENIX  pro-
       ceedings, Winter 1992.

COLOPHON
       This  page  is  part of release 3.55 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at
       http://www.kernel.org/doc/man-pages/.

4.4 Berkeley Distribution		    2012-05-04					DBOPEN(3)
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