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Linux 2.6 - man page for dbm_nextkey (linux section 3posix)

DBM_CLEARERR(P) 		    POSIX Programmer's Manual			  DBM_CLEARERR(P)

NAME
       dbm_clearerr,  dbm_close,  dbm_delete,  dbm_error,  dbm_fetch,  dbm_firstkey, dbm_nextkey,
       dbm_open, dbm_store - database functions

SYNOPSIS
       #include <ndbm.h>

       int dbm_clearerr(DBM *db);
       void dbm_close(DBM *db);
       int dbm_delete(DBM *db, datum key);
       int dbm_error(DBM *db);
       datum dbm_fetch(DBM *db, datum key);
       datum dbm_firstkey(DBM *db);
       datum dbm_nextkey(DBM *db);
       DBM *dbm_open(const char *file, int open_flags, mode_t file_mode);
       int dbm_store(DBM *db, datum key, datum content, int store_mode);

DESCRIPTION
       These functions create, access, and modify a database.

       A datum consists of at least two members, dptr and dsize.  The dptr member  points  to  an
       object that is dsize bytes in length. Arbitrary binary data, as well as character strings,
       may be stored in the object pointed to by dptr.

       The database is stored in two files. One file is a directory containing a bitmap  of  keys
       and has .dir as its suffix. The second file contains all data and has .pag as its suffix.

       The  dbm_open()	function  shall open a database. The file argument to the function is the
       pathname of the database.  The function opens two files named file.dir and file.pag.   The
       open_flags  argument  has  the  same meaning as the flags argument of open() except that a
       database opened for write-only access opens the files for read and write  access  and  the
       behavior  of the O_APPEND flag is unspecified. The file_mode argument has the same meaning
       as the third argument of open().

       The dbm_close() function shall close a database. The application shall ensure  that  argu-
       ment db is a pointer to a dbm structure that has been returned from a call to dbm_open().

       These  database	functions  shall  support  an internal block size large enough to support
       key/content pairs of at least 1023 bytes.

       The dbm_fetch() function shall read a record from  a  database.	 The  argument	db  is	a
       pointer	to  a  database  structure  that has been returned from a call to dbm_open(). The
       argument key is a datum that has been initialized by the application to the value  of  the
       key that matches the key of the record the program is fetching.

       The dbm_store() function shall write a record to a database.  The argument db is a pointer
       to a database structure that has been returned from a call to dbm_open(). The argument key
       is a datum that has been initialized by the application to the value of the key that iden-
       tifies (for subsequent reading, writing, or deleting) the record the application is  writ-
       ing.  The  argument content is a datum that has been initialized by the application to the
       value of the record the program is  writing.  The  argument  store_mode	controls  whether
       dbm_store()  replaces  any  pre-existing record that has the same key that is specified by
       the  key  argument.  The  application  shall  set  store_mode  to  either  DBM_INSERT   or
       DBM_REPLACE.  If  the  database	contains  a  record  that  matches  the  key argument and
       store_mode is DBM_REPLACE, the existing record shall be replaced with the new  record.  If
       the database contains a record that matches the key argument and store_mode is DBM_INSERT,
       the existing record shall be left unchanged and the new record ignored.	If  the  database
       does  not  contain  a  record  that  matches  the  key  argument  and store_mode is either
       DBM_INSERT or DBM_REPLACE, the new record shall be inserted in the database.

       If the sum of a key/content pair exceeds the internal block size, the result  is  unspeci-
       fied. Moreover, the application shall ensure that all key/content pairs that hash together
       fit on a single block. The dbm_store() function shall return an error in the event that	a
       disk block fills with inseparable data.

       The  dbm_delete()  function shall delete a record and its key from the database. The argu-
       ment db is a pointer to a database structure  that  has	been  returned	from  a  call  to
       dbm_open().   The  argument key is a datum that has been initialized by the application to
       the value of the key that identifies the record the program is deleting.

       The dbm_firstkey() function shall return the first key in the database. The argument db is
       a pointer to a database structure that has been returned from a call to dbm_open().

       The dbm_nextkey() function shall return the next key in the database. The argument db is a
       pointer to a database structure that has been returned from a  call  to	dbm_open().   The
       application  shall  ensure  that  the  dbm_firstkey()  function	is  called before calling
       dbm_nextkey(). Subsequent calls to dbm_nextkey() return the next key until all of the keys
       in the database have been returned.

       The dbm_error() function shall return the error condition of the database. The argument db
       is a pointer to a database structure that has been returned from a call to dbm_open().

       The dbm_clearerr() function shall clear the error condition of the database. The  argument
       db is a pointer to a database structure that has been returned from a call to dbm_open().

       The  dptr  pointers  returned by these functions may point into static storage that may be
       changed by subsequent calls.

       These functions need not be reentrant. A function that is not required to be reentrant  is
       not required to be thread-safe.

RETURN VALUE
       The dbm_store() and dbm_delete() functions shall return 0 when they succeed and a negative
       value when they fail.

       The dbm_store() function shall return 1 if it is called with a flags value  of  DBM_INSERT
       and the function finds an existing record with the same key.

       The  dbm_error()  function  shall  return 0 if the error condition is not set and return a
       non-zero value if the error condition is set.

       The return value of dbm_clearerr() is unspecified.

       The dbm_firstkey() and dbm_nextkey() functions shall return a key datum. When the  end  of
       the  database  is  reached,  the  dptr member of the key is a null pointer. If an error is
       detected, the dptr member of the key shall be a null pointer and the  error  condition  of
       the database shall be set.

       The  dbm_fetch()  function  shall  return  a  content datum.  If no record in the database
       matches the key or if an error condition has been detected in the database, the dptr  mem-
       ber of the content shall be a null pointer.

       The  dbm_open()	function  shall  return a pointer to a database structure. If an error is
       detected during the operation, dbm_open() shall return a ( DBM *)0.

ERRORS
       No errors are defined.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       The following code can be used to traverse the database:

	      for(key = dbm_firstkey(db); key.dptr != NULL; key = dbm_nextkey(db))

       The dbm_* functions provided in this library should not be confused in any way with  those
       of a general-purpose database management system. These functions do not provide for multi-
       ple search keys per entry, they do not protect against multi-user access (in  other  words
       they do not lock records or files), and they do not provide the many other useful database
       functions that are found in more robust database management systems. Creating and updating
       databases  by  use of these functions is relatively slow because of data copies that occur
       upon hash collisions. These functions are useful for applications requiring fast lookup of
       relatively static information that is to be indexed by a single key.

       Note that a strictly conforming application is extremely limited by these functions: since
       there is no way to determine that the keys in use do  not  all  hash  to  the  same  value
       (although that would be rare), a strictly conforming application cannot be guaranteed that
       it can store more than one block's worth of data in the database.  As long as a key colli-
       sion  does not occur, additional data may be stored, but because there is no way to deter-
       mine whether an error is  due  to  a  key  collision  or  some  other  error  condition	(
       dbm_error()  being  effectively	a Boolean), once an error is detected, the application is
       effectively limited to guessing what the error might be if it  wishes  to  continue  using
       these functions.

       The dbm_delete() function need not physically reclaim file space, although it does make it
       available for reuse by the database.

       After calling dbm_store() or dbm_delete() during a pass through the keys by dbm_firstkey()
       and  dbm_nextkey(),  the  application  should reset the database by calling dbm_firstkey()
       before again calling dbm_nextkey(). The contents of these files are  unspecified  and  may
       not be portable.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       open() , the Base Definitions volume of IEEE Std 1003.1-2001, <ndbm.h>

COPYRIGHT
       Portions  of  this  text  are  reprinted  and  reproduced in electronic form from IEEE Std
       1003.1, 2003 Edition, Standard for Information Technology  --  Portable	Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
       the Institute of Electrical and Electronics Engineers, Inc and  The  Open  Group.  In  the
       event  of  any  discrepancy  between this version and the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				  DBM_CLEARERR(P)


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