Reference

db_dbm(3db)

dbminit, fetch, store, delete, firstkey, nextkey

NAME

dbm - dbminit, fetch, store, delete, firstkey, nextkey

ndbm - dbm_open, dbm_close, dbm_fetch, dbm_store, dbm_delete,
dbm_firstkey, dbm_nextkey, dbm_error, dbm_clearerr

SYNOPSIS

#define DB_DBM_HSEARCH    1
#include <db2/db.h>
typedef struct {
	char *dptr;
	int dsize;
} datum;

DBM FUNCTIONS

int
dbminit(char *file);
datum
fetch(datum key);
int
store(datum key, datum content);
int
delete(datum key);
datum
firstkey(void);
datum
nextkey(datum key);

NDBM FUNCTIONS

DBM *
dbm_open(char *file, int flags, int mode);
void
dbm_close(DBM *db);
datum
dbm_fetch(DBM *db, datum key);
int
dbm_store(DBM *db, datum key, datum content, int flags);
int
dbm_delete(DBM *db, datum key);
datum
dbm_firstkey(DBM *db);
datum
dbm_nextkey(DBM *db);
int
dbm_error(DBM *db);
int
dbm_clearerr(DBM *db);

DESCRIPTION

The dbm and ndbm interfaces to the DB library are intended to provide source code compatibility for historic applications. They are not recommended for any other purpose. The historic dbm and ndbm database format is not supported, and databases previously built using the real dbm or ndbm libraries cannot be read by the DB functions.

To compile dbm or ndbm applications, replace the application's #include of the dbm or ndbm include file (e.g., ``#include <dbm.h>'' or ``#include <ndbm.h>'') with the following two lines:

#define DB_DBM_HSEARCH 1
#include <db2/db.h>

and recompile. If the application attempts to load against a dbm library (e.g., ``-ldbm''), remove the library from the load line.

Keys and contents are described by the datum typedef. A datum specifies a string of dsize bytes pointed to by dptr. Arbitrary binary data, as well as normal text strings, are allowed.

DBM FUNCTIONS

Before a database can be accessed, it must be opened by dbminit. This will open and/or create the database file.db. If created, the database file is created read/write by owner only (as described in chmod(2)) and modified by the process' umask value at the time of creation (see umask(2)). The group ownership of created files is based on the system and directory defaults, and is not further specified by DB.

Once open, the data stored under a key is accessed by fetch and data is placed under a key by store. A key (and its associated contents) is deleted by delete. A linear pass through all keys in a database may be made, in an (apparently) random order, by use of firstkey and nextkey. Firstkey will return the first key in the database. With any key nextkey will return the next key in the database. This code will traverse the data base:

for (key = firstkey(); key.dptr != NULL; key = nextkey(key))

NDBM FUNCTIONS

Before a database can be accessed, it must be opened by dbm_open. This will open and/or create the database file file.db depending on the flags parameter (see open(2)). If created, the database file is created with mode mode (as described in chmod(2)) and modified by the process' umask value at the time of creation (see umask(2)). The group ownership of created files is based on the system and directory defaults, and is not further specified by DB.

Once open, the data stored under a key is accessed by dbm_fetch and data is placed under a key by dbm_store. The flags field can be either DBM_INSERT or DBM_REPLACE. DBM_INSERT will only insert new entries into the database and will not change an existing entry with the same key. DBM_REPLACE will replace an existing entry if it has the same key. A key (and its associated contents) is deleted by dbm_delete. A linear pass through all keys in a database may be made, in an (apparently) random order, by use of dbm_firstkey and dbm_nextkey. Dbm_firstkey will return the first key in the database. Dbm_nextkey will return the next key in the database. This code will traverse the data base:

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

Dbm_error returns non-zero when an error has occurred reading or writing the database. Dbm_clearerr resets the error condition on the named database.

COMPATIBILITY NOTES

The historic dbm and ndbm libraries created two underlying database files, traditionally named file.dir and file.pag. The DB library creates a single database file named file.db. Applications that are aware of the underlying database file names may require additional source code modifications.

The historic dbminit interface required that the underlying ``.dir'' and ``.pag'' files already exist (empty databases were created by creating zero-length ``.dir'' and ``.pag'' files). Applications that expect to create databases using this method may require additional source code modifications.

The historic dbm_dirfno and dbm_pagfno macros are supported, but will return identical file descriptors as there is only a single underlying file used by the DB hashing access method. Applications using both file descriptors for locking may require additional source code modifications.

If an application using the ndbm interface exits without closing the database, it may lose updates because the DB library buffers all writes. Such applications will require additional source code modifications to work correctly with the DB library.

DBM DIAGNOSTICS

The dbminit function returns -1 on failure, setting errno, and 0 on success.

The fetch function sets the returned datum's dptr field to NULL on failure, setting errno, and returns a non-NULL dptr on success.

The store function returns -1 on failure, setting errno, and 0 on success.

The delete function returns -1 on failure, setting errno, and 0 on success.

The firstkey function sets the returned datum's dptr field to NULL on failure, setting errno, and returns a non-NULL dptr on success.

The nextkey function sets the returned datum's dptr field to NULL on failure, setting errno, and returns a non-NULL dptr on success.

NDBM DIAGNOSTICS

The dbm_open function returns NULL on failure, setting errno, and 0 on success.

The dbm_fetch function sets the returned datum's dptr field to NULL on failure, setting errno, and returns a non-NULL dptr on success.

The dbm_store function returns -1 on failure, setting errno, 0 on success, and 1 if DBM_INSERT was set and the specified key already existed in the database.

The dbm_delete function returns -1 on failure, setting errno, and 0 on success.

The dbm_firstkey function sets the returned datum's dptr field to NULL on failure, setting errno, and returns a non-NULL dptr on success.

The dbm_nextkey function sets the returned datum's dptr field to NULL on failure, setting errno, and returns a non-NULL dptr on success.

The dbm_error function returns -1 on failure, setting errno, and 0 on success.

The dbm_clearerr function returns -1 on failure, setting errno, and 0 on success.

ERRORS

The dbminit function may fail and return errno for any of the errors specified for the following DB and library functions: dbm_close(3), and dbm_open(3).

The fetch function may fail and return errno for any of the errors specified for the following DB and library functions: dbm_fetch(3).

The store function may fail and return errno for any of the errors specified for the following DB and library functions: dbm_store(3).

The delete function may fail and return errno for any of the errors specified for the following DB and library functions: dbm_delete(3).

The firstkey function may fail and return errno for any of the errors specified for the following DB and library functions: dbm_firstkey(3).

The nextkey function may fail and return errno for any of the errors specified for the following DB and library functions: dbm_nextkey(3).

The dbm_open function may fail and return errno for any of the errors specified for the following DB and library functions: db_open(3), and memset(3).

The dbm_close function may fail and return errno for any of the errors specified for the following DB and library functions: DB->close(3).

The dbm_fetch function may fail and return errno for any of the errors specified for the following DB and library functions: DB->get(3), and memset(3).

The dbm_store function may fail and return errno for any of the errors specified for the following DB and library functions: DB->put(3), and memset(3).

The dbm_delete function may fail and return errno for any of the errors specified for the following DB and library functions: memset(3).

The dbm_firstkey function may fail and return errno for any of the errors specified for the following DB and library functions: DB->cursor(3), and memset(3).

The dbm_nextkey function may fail and return errno for any of the errors specified for the following DB and library functions: DB->cursor(3), and memset(3).

SEE ALSO

The DB library is a family of groups of functions that provides a modular programming interface to transactions and record-oriented file access. The library includes support for transactions, locking, logging and file page caching, as well as various indexed access methods. Many of the functional groups (e.g., the file page caching functions) are useful independent of the other DB functions, although some functional groups are explicitly based on other functional groups (e.g., transactions and logging). For a general description of the DB package, see db_intro(3).

db_archive(1), db_checkpoint(1), db_deadlock(1), db_dump(1), db_load(1), db_recover(1), db_stat(1), db_intro(3), db_appinit(3), db_cursor(3), db_dbm(3), db_internal(3), db_lock(3), db_log(3), db_mpool(3), db_open(3), db_thread(3), db_txn(3)

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