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
       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 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
       identifies  (for  subsequent  reading, writing, or deleting) the record the application is
       writing. 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
       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 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
       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 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
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .