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HTML
208 lines
8.2 KiB
HTML
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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
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<title>Dbstl examples</title>
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<link rel="stylesheet" href="gettingStarted.css" type="text/css" />
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<meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
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<link rel="start" href="index.html" title="Berkeley DB Programmer's Reference Guide" />
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<link rel="up" href="stl.html" title="Chapter 7. Standard Template Library API" />
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<link rel="prev" href="stl_usecase.html" title="Dbstl typical use cases" />
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<link rel="next" href="stl_db_usage.html" title="Berkeley DB configuration" />
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</head>
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<body>
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<div xmlns="" class="navheader">
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<div class="libver">
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<p>Library Version 11.2.5.2</p>
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</div>
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<table width="100%" summary="Navigation header">
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<tr>
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<th colspan="3" align="center">Dbstl examples</th>
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</tr>
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<tr>
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<td width="20%" align="left"><a accesskey="p" href="stl_usecase.html">Prev</a> </td>
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<th width="60%" align="center">Chapter 7. Standard Template Library API</th>
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<td width="20%" align="right"> <a accesskey="n" href="stl_db_usage.html">Next</a></td>
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</tr>
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</table>
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<hr />
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</div>
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<div class="sect1" lang="en" xml:lang="en">
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<div class="titlepage">
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<div>
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<div>
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<h2 class="title" style="clear: both"><a id="stl_examples"></a>Dbstl examples</h2>
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</div>
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</div>
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</div>
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<p>
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Because dbstl is so much like C++ STL, its usage exactly mirrors that
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of C++ STL, with the exception of a few optional Berkeley DB specific
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configurations. In fact, the only difference between a program using
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dbstl and one using C++ STL is the class names. That is,
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<code class="classname">vector</code> becomes <code class="classname">db_vector</code>,
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and <code class="classname">map</code> becomes <code class="classname">db_map</code>.
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</p>
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<p>
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The typical procedure for using dbstl is:
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</p>
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<div class="orderedlist">
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<ol type="1">
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<li>
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<p>
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Optionally create and open your own Berkeley DB environment and
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database handles using the DB C++ API. If you perform these opens
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using the C++ API, make sure to perform necessary
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environment and database configurations at that time.
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</p>
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</li>
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<li>
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<p>
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Optionally pass environment and database handles to dbstl container
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constructors when you create dbstl container objects. Note that you
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can create a dbstl container without passing it an environment and
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database object. When you do this, an internal anonymous database
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is created for you. In this situation, dbstl provides no data
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persistence guarantees.
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</p>
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</li>
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<li>
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<p>
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Perform dbstl-specific configurations. For example, you can
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configure cursor open flags, as well as database
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access for autocommit. You can also configure callback functions.
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</p>
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</li>
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<li>
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<p>
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Interact with the data contained in your Berkeley DB databases using
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dbstl containers and iterators. This usage of dbstl is identical to
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C++ STL container and iterator usage.
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</p>
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</li>
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<li>
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<p>
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At this time, you can also use dbstl calls that are specific to Berkeley DB.
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For example, you can use Berkeley DB specific calls that manage transaction
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begin/commit/abort, handle registration, and so forth. While these
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calls are part of dbstl, they have no equivalence in the C++ STL
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APIs.
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</p>
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</li>
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<li>
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<p>
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When your application is done using Berkeley DB, you do not need to
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explicitly close any Berkeley DB handles (environments, database,
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cursors, and so forth). Dbstl automatically closes all such handles
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for you.
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</p>
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</li>
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</ol>
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</div>
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<p>
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For examples of dbstl usage, see the example programs in the
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<code class="filename">$db/examples_stl</code> directory.
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</p>
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<p>
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The following program listing provides two code fragments. You can
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find more example code in the <code class="filename">dbstl/examples/</code>
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and <code class="filename">dbstl/test</code> directories.
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</p>
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<pre class="programlisting">//////////////// Code Snippet 1 ////////////////
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db_vector<int, ElementHolder<int> > vctr(100);
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for (int i = 0; i < 100; i++)
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vctr[i] = i;
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for (int i = 0; i < 100; i++) {
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cout<<"\nvctr["<<i<<"] : "<<vctr[i];
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vctr[i] = vctr[i] * vctr[i];
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cout<<"\nvctr["<<i<<"] squre : "<<vctr[i];
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}
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//////////////// Code Snippet 2 ////////////////
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typedef db_map<char *, const char *, ElementHolder<const char *> >
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strmap_t2;
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strmap_t2 strmap;
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char str[2], str2[2];
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str[1] = str2[1] = '\0';
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for (char c = 0; c < 26; c++) {
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str[0] = c + 'a';
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str2[0] = 'z' - c;
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strmap[str] = str2;
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}
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for (strmap_t2::iterator itr = strmap.begin(); itr != strmap.end(); ++itr)
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cout<<endl<<itr->first<<" : "<<itr->second;
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using namespace dbstl;
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dbstl::db_map<char, int> v;
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v['i'] = 1;
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cout<<v['i'];
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dbstl::db_map<char *, char *> name_addr_map;
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// The strings rather than the memory pointers are stored into DB.
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name_addr_map["Alex"] = "Sydney Australia";
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name_addr_map["David"] = "Shenzhen China";
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cout<<"Alex's address:"<<name_addr_map["Alex"];
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dbstl::db_vector<Person> vi;
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// Some callback configurations follow here.
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// The strings and objects rather than pointers are stored into DB.
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Person obj("David Zhao", "Oracle", new Office("Boston", "USA"));
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vi.push_back(obj); // More person storage.
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for (int I = 0; I < vi.size(); I++)
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cout<<vi[I]; </pre>
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<p>
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The first snippet initializes a db_vector container of 100 elements,
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with an in-memory anonymous database internally created by dbstl. The
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only difference between this and C++ STL is dbstl requires one more
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<code class="literal">type</code> parameter:
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<em class="parameter"><code>ElementHolder<int></code></em>. The
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<code class="classname">ElementHolder</code> class template should be used for
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every type of dbstl container that will store C++ primitive data types,
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such as <code class="literal">int</code>, <code class="literal">float</code>,
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<code class="literal">char *</code>, <code class="literal">wchar_t *</code>, and so forth. But these
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class templates should not be used for class types for reasons that we
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explain in the following chapters.
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</p>
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<p>
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In the second code snippet, the assignment:
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</p>
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<pre class="programlisting">strmap[str] = str2;</pre>
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<p>
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is used to store a string pair (<code class="literal">(str, str2)</code>) instead
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of pointers to the underlying database.
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</p>
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<p>
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The rest of the code used in these snippets is identical to the code
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you would use for C++ STL containers. However, by using dbstl, you are
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storing data into a Berkeley DB database. If you create your own
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database with backing files on disk, your data or objects can persist
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and be restored when the program runs again.
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</p>
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</div>
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<div class="navfooter">
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<hr />
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<table width="100%" summary="Navigation footer">
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<tr>
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<td width="40%" align="left"><a accesskey="p" href="stl_usecase.html">Prev</a> </td>
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<td width="20%" align="center">
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<a accesskey="u" href="stl.html">Up</a>
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</td>
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<td width="40%" align="right"> <a accesskey="n" href="stl_db_usage.html">Next</a></td>
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</tr>
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<tr>
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<td width="40%" align="left" valign="top">Dbstl typical use cases </td>
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<td width="20%" align="center">
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<a accesskey="h" href="index.html">Home</a>
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</td>
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<td width="40%" align="right" valign="top"> Berkeley DB configuration</td>
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</tr>
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</table>
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</div>
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</body>
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</html>
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