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DBM_CLEARERR(3P)	   POSIX Programmer's Manual	      DBM_CLEARERR(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

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.

       A database shall be stored in one or two files. When one file is	 used,
       the  name  of the database file shall be formed by appending the suffix
       .db to the file argument given to dbm_open().  When two files are used,
       the  names  of the database files shall be formed by appending the suf‐
       fixes .dir and .pag respectively to the file argument.

       The dbm_open() function shall open a database. The file argument to the
       function	 is  the pathname of the database. 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_open()	  function  need  not  accept  pathnames  longer  than
       {PATH_MAX}−4 bytes (including the terminating null), or pathnames  with
       a  last	component longer than {NAME_MAX}−4 bytes (excluding the termi‐
       nating null).

       The dbm_close() function shall close a database. The application	 shall
       ensure  that  argument 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 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 matches the
       key of the record the program is fetching.

       The  dbm_store() function shall write a record to a 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
       (for  subsequent reading, writing, or deleting) the record the applica‐
       tion is writing. The argument content is a datum that has been initial‐
       ized by the application to the value of the record the program is writ‐
       ing. 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 data‐
       base 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 unspecified. 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 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 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 data‐
       base. 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 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  member  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 multiple 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
       collision  does	not  occur, additional data may be stored, but because
       there is no way to determine whether an error is due to a key collision
       or  some	 other	error condition (dbm_error() being effectively a Bool‐
       ean), 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_nex‐
       tkey().	The contents of these files are unspecified  and  may  not  be
       portable.

       Applications  should  take care that database pathname arguments speci‐
       fied to dbm_open() are not prefixes of unrelated files. This  might  be
       done, for example, by placing databases in a separate directory.

       Since some implementations use three characters for a suffix and others
       use four characters for a suffix, applications should ensure  that  the
       maximum	portable  pathname  length  passed to dbm_open() is no greater
       than {PATH_MAX}−4 bytes, with the last component	 of  the  pathname  no
       greater than {NAME_MAX}−4 bytes.

RATIONALE
       Previously  the	standard  required  the	 database  to be stored in two
       files, one file being a directory containing a bitmap of keys and  hav‐
       ing  .dir as its suffix. The second file containing all data and having
       .pag as its suffix. This has been changed not to specify the use of the
       files  and  to allow newer implementations of the Berkeley DB interface
       using a single file that have evolved while remaining  compatible  with
       the  application programming interface. The standard developers consid‐
       ered removing the specific suffixes altogether but  decided  to	retain
       them  so	 as  not  to pollute the application file name space more than
       necessary and to allow for portable backups of the database.

FUTURE DIRECTIONS
       None.

SEE ALSO
       open()

       The Base Definitions volume of POSIX.1‐2008, <ndbm.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) 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 original Standard can be  obtained	online
       at http://www.unix.org/online.html .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013		      DBM_CLEARERR(3P)
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