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<th width="60%" align="center">Appendix 2.
Historic Interfaces
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<div class="sect1" lang="en" xml:lang="en">
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<div>
<div>
<h2 class="title" style="clear: both"><a id="dbm"></a>dbm/ndbm</h2>
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<pre class="programlisting">#define DB_DBM_HSEARCH 1
#include <db.h>
typedef struct {
char *dptr;
int dsize;
} datum; </pre>
<p>
<span class="bold"><strong>Dbm Functions</strong></span>
</p>
<pre class="programlisting">int
dbminit(char *file);
int
dbmclose();
datum
fetch(datum key);
int
store(datum key, datum content);
int
delete(datum key);
datum
firstkey(void);
datum
nextkey(datum key);</pre>
<p>
<span class="bold"><strong>Ndbm Functions</strong></span>
</p>
<pre class="programlisting">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); </pre>
<p>
The dbm functions are intended to provide high-performance
implementations and source code compatibility for applications written
to historic interfaces. They are not recommended for any other
purpose. The historic dbm database format <span class="bold"><strong>is not
supported</strong></span>, and databases previously built using the real
dbm libraries cannot be read by the Berkeley DB functions.
</p>
<p>
To compile dbm applications, replace the application's <span class="bold"><strong>#include</strong></span> of the dbm or ndbm include file (for
example, <span class="bold"><strong>#include <dbm.h></strong></span> or
<span class="bold"><strong>#include <ndbm.h></strong></span>) with the
following two lines:
</p>
<pre class="programlisting">#define DB_DBM_HSEARCH 1
#include <db.h></pre>
<p>
and recompile. If the application attempts to load against a dbm
library (for example, <span class="bold"><strong>-ldbm</strong></span>), remove
the library from the load line.
</p>
<p>
<span class="bold"><strong>Key</strong></span> and
<span class="bold"><strong>content</strong></span> parameters are objects described by the
<span class="bold"><strong>datum</strong></span> typedef. A
<span class="bold"><strong>datum</strong></span> specifies a string of
<span class="bold"><strong>dsize</strong></span> bytes pointed to by
<span class="bold"><strong>dptr</strong></span>. Arbitrary binary data, as well as normal
text strings, are allowed.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="dbmfunctions"></a>Dbm Functions</h3>
</div>
</div>
</div>
<p>
Before a database can be accessed, it must be opened by dbminit. This
will open and/or create the database
<span class="bold"><strong>file.db</strong></span>. If created, the database file is
created read/write by owner only (as described in
<span class="bold"><strong>chmod</strong></span>(2)) and modified by the process' umask
value at the time of creation (see
<span class="bold"><strong>umask</strong></span>(2)). The group ownership of created
files is based on the system and directory defaults, and is not
further specified by Berkeley DB.
</p>
<p>
A database may be closed, and any held resources released, by calling
dbmclose.
</p>
<p>
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)
are deleted by delete. A linear pass through all keys in a database
may be made, in an (apparently) random order, by using firstkey and
nextkey. The firstkey method will return the first key in the
databaseThe nextkey method will return the next key in satabase.
</p>
<p>
The following code will traverse the database:
</p>
<pre class="programlisting">for (key = firstkey(key);
key.dptr != NULL; key = nextkey(key)) {
...
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="ndbmfunctions"></a>Ndbm Functions</h3>
</div>
</div>
</div>
<p>
Before a database can be accessed, it must be opened by dbm_open. This
will open and/or create the database file
<span class="bold"><strong>file.db</strong></span>, depending on the flags parameter (see
<span class="bold"><strong>open</strong></span>(2)). If created, the database
file is created with mode <span class="bold"><strong>mode</strong></span> (as
described in <span class="bold"><strong>chmod</strong></span>(2)) and modified
by the process' umask value at the time of creation (see <span class="bold"><strong>umask</strong></span>(2)). The group ownership of created
files is based on the system and directory defaults, and is not
further specified by Berkeley DB.
</p>
<p>
Once open, the data stored under a key is accessed by dbm_fetch, and
data is placed under a key by dbm_store. The
<span class="bold"><strong>flags</strong></span> field can be either
<span class="bold"><strong>DBM_INSERT</strong></span> or
<span class="bold"><strong>DBM_REPLACE</strong></span>.
<span class="bold"><strong>DBM_INSERT</strong></span> will only insert new entries into
the database, and will not change an existing entry with the same key.
<span class="bold"><strong>DBM_REPLACE</strong></span> will replace an existing
entry if it has the same key. A key (and its associated contents) are
deleted by dbm_delete. A linear pass through all keys in a database
may be made, in an (apparently) random order, by using dbm_firstkey
and dbm_nextkey. The dbm_firstkey method will return the first key in
the database. The dbm_nextkey method will return the next key in the
database.
</p>
<p>
The following code will traverse the database:
</p>
<pre class="programlisting">for (key = dbm_firstkey(db);
key.dptr != NULL; key = dbm_nextkey(db)) {
...
} </pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="dbm_compat_notes"></a>Compatibility Notes</h3>
</div>
</div>
</div>
<p>
The historic dbm library created two underlying database files,
traditionally named <span class="bold"><strong>file.dir</strong></span> and
<span class="bold"><strong>file.pag</strong></span>. The Berkeley DB library
creates a single database file named <span class="bold"><strong>file.db</strong></span>. Applications that are aware of the
underlying database filenames may require additional source code
modifications.
</p>
<p>
The historic dbminit function required that the underlying <span class="bold"><strong>.dir</strong></span> and <span class="bold"><strong>.pag</strong></span>
files already exist (empty databases were created by first manually
creating zero-length <span class="bold"><strong>.dir</strong></span> and
<span class="bold"><strong>.pag</strong></span> files). Applications that
expect to create databases using this method may require additional
source code modifications.
</p>
<p>
The historic dbm_dirfno and dbm_pagfno macros are supported, but will
return identical file descriptors because there is only a single
underlying file used by the Berkeley DB hashing access method.
Applications using both file descriptors for locking may require
additional source code modifications.
</p>
<p>
If applications using the dbm function exits without first closing the
database, it may lose updates because the Berkeley DB library buffers
writes to underlying databases. Such applications will require
additional source code modifications to work correctly with the
Berkeley DB library.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="dbm_diagnostics"></a>Dbm Diagnostics</h3>
</div>
</div>
</div>
<p>
The dbminit function returns -1 on failure, setting <span class="bold"><strong>errno</strong></span>, and 0 on success.
</p>
<p>
The fetch function sets the <span class="bold"><strong>dptr</strong></span>
field of the returned <span class="bold"><strong>datum</strong></span> to NULL
on failure, setting <span class="bold"><strong>errno</strong></span>, and
returns a non-NULL <span class="bold"><strong>dptr</strong></span> on success.
</p>
<p>
The store function returns -1 on failure, setting <span class="bold"><strong>errno</strong></span>, and 0 on success.
</p>
<p>
The delete function returns -1 on failure, setting <span class="bold"><strong>errno</strong></span>, and 0 on success.
</p>
<p>
The firstkey function sets the <span class="bold"><strong>dptr</strong></span>
field of the returned <span class="bold"><strong>datum</strong></span> to NULL
on failure, setting <span class="bold"><strong>errno</strong></span>, and
returns a non-NULL <span class="bold"><strong>dptr</strong></span> on success.
</p>
<p>
The nextkey function sets the <span class="bold"><strong>dptr</strong></span>
field of the returned <span class="bold"><strong>datum</strong></span> to NULL
on failure, setting <span class="bold"><strong>errno</strong></span>, and
returns a non-NULL <span class="bold"><strong>dptr</strong></span> on success.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="dbm_errors"></a>Dbm Errors</h3>
</div>
</div>
</div>
<p>
The dbminit, fetch, store, delete, firstkey, and nextkey functions may
fail and return an error for errors specified for other Berkeley DB
and C library or system functions.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="ndbm_diagnostics"></a>Ndbm Diagnostics</h3>
</div>
</div>
</div>
<p>
The dbm_close method returns non-zero when an error has occurred
reading or writing the database.
</p>
<p>
The dbm_close method resets the error condition on the named database.
</p>
<p>
The dbm_open function returns NULL on failure, setting <span class="bold"><strong>errno</strong></span>, and a DBM reference on success.
</p>
<p>
The dbm_fetch function sets the <span class="bold"><strong>dptr</strong></span>
field of the returned <span class="bold"><strong>datum</strong></span> to NULL
on failure, setting <span class="bold"><strong>errno</strong></span>, and
returns a non-NULL <span class="bold"><strong>dptr</strong></span> on success.
</p>
<p>
The dbm_store function returns -1 on failure, setting <span class="bold"><strong>errno</strong></span>, 0 on success, and 1 if DBM_INSERT was
set and the specified key already existed in the database.
</p>
<p>
The dbm_delete function returns -1 on failure, setting <span class="bold"><strong>errno</strong></span>, and 0 on success.
</p>
<p>
The dbm_firstkey function sets the <span class="bold"><strong>dptr</strong></span> field of the returned <span class="bold"><strong>datum</strong></span> to NULL on failure, setting <span class="bold"><strong>errno</strong></span>, and returns a non-NULL <span class="bold"><strong>dptr</strong></span> on success.
</p>
<p>
The dbm_nextkey function sets the <span class="bold"><strong>dptr</strong></span> field of the returned <span class="bold"><strong>datum</strong></span> to NULL on failure, setting <span class="bold"><strong>errno</strong></span>, and returns a non-NULL <span class="bold"><strong>dptr</strong></span> on success.
</p>
<p>
The dbm_close function returns -1 on failure, setting <span class="bold"><strong>errno</strong></span>, and 0 on success.
</p>
<p>
The dbm_close function returns -1 on failure, setting <span class="bold"><strong>errno</strong></span>, and 0 on success.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="ndbm_errors"></a>Ndbm Errors</h3>
</div>
</div>
</div>
<p>
The dbm_open, dbm_close, dbm_fetch, dbm_store, dbm_delete,
dbm_firstkey, and dbm_nextkey functions may fail and return an error
for errors specified for other Berkeley DB and C library or system
functions.
</p>
</div>
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