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    Command:

    dbopen

    
    
    

    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  inter-
           faces.   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 for-
           mat 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 struc-
           ture 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  structure  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,
    
                  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  inconsis-
                  tent  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  suc-
                  cess, and 1 if the specified key was not in the file.
    
           fd     A pointer to a routine which returns a file descriptor represen-
                  tative of the underlying database.  A file descriptor  referenc-
                  ing  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 databases.   fd  rou-
                  tines  return -1 on error (setting errno), and the file descrip-
                  tor on success.
    
           get    A pointer  to  a  routine  which  is  the  interface  for  keyed
                  retrieval from the database.  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  struc-
                         ture.  (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
    
                  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, replacing 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 referenced 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.  Modifications 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.
    
                  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 routine 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 suc-
                  cess.
    
       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 unlim-
           ited 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 spec-
           ified 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  mismatch
                  between the version number of file and the software.
    
           The  close routines may fail and set errno for any of the errors speci-
           fied for the library routines close(2), read(2), write(2), free(3),  or
           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, lock-
           ing, or transactions.
    
    
    

    SEE ALSO

           btree(3), hash(3), mpool(3), recno(3)
    
           LIBTP:  Portable, Modular Transactions for UNIX, Margo Seltzer, Michael
           Olson, USENIX proceedings, Winter 1992.
    
    
    

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

    
    
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