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<p>Library Version 18.1.40</p>
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<th width="60%" align="center">Chapter 8. Berkeley DB Architecture </th>
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<div class="sect1" lang="en" xml:lang="en">
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<h2 class="title" style="clear: both"><a id="arch_apis"></a>Programmatic APIs</h2>
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<dl>
<dt>
<span class="sect2">
<a href="arch_apis.html#idm140654539078640">C</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="arch_apis.html#idm140654539025952">C++</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="arch_apis.html#idm140654539043616">STL</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="arch_apis.html#idm140654539044032">Java</a>
</span>
</dt>
<dt>
<span class="sect2">
<a href="arch_apis.html#idm140654539013824">Dbm/Ndbm, Hsearch</a>
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<p>
The Berkeley DB subsystems can be accessed through
interfaces from multiple languages. Applications can use
Berkeley DB via C, C++ or Java, as well as a variety of
scripting languages such as Perl, Python, Ruby or Tcl.
Environments can be shared among applications written by using
any of these interfaces. For example, you might have a local
server written in C or C++, a script for an administrator
written in Perl or Tcl, and a Web-based user interface written
in Java -- all sharing a single database environment.
</p>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539078640"></a>C</h3>
</div>
</div>
</div>
<p>
The Berkeley DB library is written entirely in ANSI C. C
applications use a single include file:
</p>
<pre class="programlisting">#include <db.h></pre>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539025952"></a>C++</h3>
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<p>
The C++ classes provide a thin wrapper around the C API,
with the major advantages being improved encapsulation and
an optional exception mechanism for errors. C++
applications use a single include file:
</p>
<pre class="programlisting">#include <db_cxx.h></pre>
<p>
The classes and methods are named in a fashion that
directly corresponds to structures and functions in the C
interface. Likewise, arguments to methods appear in the
same order as the C interface, except to remove the
explicit <span class="bold"><strong>this</strong></span> pointer.
The #defines used for flags are identical between the C
and C++ interfaces.
</p>
<p>
As a rule, each C++ object has exactly one structure
from the underlying C API associated with it. The C
structure is allocated with each constructor call and
deallocated with each destructor call. Thus, the rules the
user needs to follow in allocating and deallocating
structures are the same between the C and C++
interfaces.
</p>
<p>
To ensure portability to many platforms, both new and
old, Berkeley DB makes as few assumptions as possible
about the C++ compiler and library. For example, it does
not expect STL, templates, or namespaces to be available.
The newest C++ feature used is exceptions, which are used
liberally to transmit error information. Even the use of
exceptions can be disabled at runtime.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539043616"></a>STL</h3>
</div>
</div>
</div>
<p>
dbstl is an C++ STL style API for Berkeley DB, based on
the C++ API above. With it, you can store data/objects of
any type into or retrieve them from Berkeley DB databases
as if you are using C++ STL containers. The full
functionality of Berkeley DB can still be utilized via
dbstl with little performance overhead, e.g. you can use
all transaction and/or replication functionality of
Berkeley DB.
</p>
<p>
dbstl container/iterator class templates reside in
header files dbstl_vector.h, dbstl_map.h and dbstl_set.h.
Among them, dbstl_vector.h contains dbstl::db_vector and
its iterators; dbstl_map.h contains dbstl::db_map,
dbstl::db_multimap and their iterators; dbstl_set.h
contains dbstl::db_set and dbstl::db_multiset and their
iterators. You should include needed header file(s) to use
the container/iterator. Note that we don't use the file
name with no extention --- To use dbstl::db_vector, you
should do this:
</p>
<pre class="programlisting">#include "dbstl_vector.h"</pre>
<p>
rather than this:
</p>
<pre class="programlisting">#include "dbstl_vector"</pre>
<p>
And these header files reside in "stl" directory inside
Berkeley DB source root directory. If you have installed
Berkeley DB, they are also available in the "include"
directory in the directory where Berkeley DB is installed.
</p>
<p>
Apart from the above three header files, you may also
need to include db_exception.h and db_utility.h files. The
db_exception.h file contains all exception classes of
dbstl, which integrate seamlessly with Berkeley DB C++ API
exceptions and C++ standard exception classes in std
namespace. And the db_utility.h file contains the
DbstlElemTraits which helps you to store complex objects.
These five header files are all that you need to include
in order to make use of dbstl.
</p>
<p>
All symbols of dbstl, including classes, class
templates, global functions, etc, reside in the namespace
"dbstl", so in order to use them, you may also want to do
this:
</p>
<pre class="programlisting">using namespace dbstl;</pre>
<p>
The dbstl library is always at the same place where
Berkeley DB library is located, you will need to build it
and link with it to use dbstl.
</p>
<p>
While making use of dbstl, you will probably want to
create environment or databases directly, or set/get
configurations to Berkeley DB environment or databases,
etc. You are allowed to do so via Berkeley DB C/C++ API.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539044032"></a>Java</h3>
</div>
</div>
</div>
<p>
The Java classes provide a layer around the C API that
is almost identical to the C++ layer. The classes and
methods are, for the most part identical to the C++ layer.
Berkeley DB constants and #defines are represented as
"static final int" values. Error conditions are
communicated as Java exceptions.
</p>
<p>
As in C++, each Java object has exactly one structure
from the underlying C API associated with it. The Java
structure is allocated with each constructor or open call,
but is deallocated only by the Java garbage collector.
Because the timing of garbage collection is not
predictable, applications should take care to do a close
when finished with any object that has a close
method.
</p>
</div>
<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="idm140654539013824"></a>Dbm/Ndbm, Hsearch</h3>
</div>
</div>
</div>
<p>
Berkeley DB supports the standard UNIX <a href="../api_reference/C/dbm.html" class="olink">dbm</a> and
<a href="../api_reference/C/hsearch.html" class="olink">hsearch</a> interfaces. After including a new header file
and recompiling, programs will run orders of magnitude
faster, and underlying databases can grow as large as
necessary. Also, historic <a href="../api_reference/C/dbm.html" class="olink">dbm</a> applications can fail once
some number of entries are inserted into the database, in
which the number depends on the effectiveness of the
internal hashing function on the particular data set. This
is not a problem with Berkeley DB.
</p>
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