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<title>Creates a PDO instance representing a connection to a database</title>
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<h1 class="refname">PDO::__construct</h1>
<p class="verinfo">(PHP 5 >= 5.1.0, PECL pdo >= 0.1.0)</p><p class="refpurpose"><span class="refname">PDO::__construct</span> — <span class="dc-title">
Creates a PDO instance representing a connection to a database
</span></p>
</div>
<div class="refsect1 description" id="refsect1-pdo.construct-description">
<h3 class="title">Description</h3>
<div class="constructorsynopsis dc-description">
<span class="modifier">public</span> <span class="methodname"><strong>PDO::__construct()</strong></span>
( <span class="methodparam"><span class="type">string</span> <code class="parameter">$dsn</code></span>
[, <span class="methodparam"><span class="type">string</span> <code class="parameter">$username</code></span>
[, <span class="methodparam"><span class="type">string</span> <code class="parameter">$password</code></span>
[, <span class="methodparam"><span class="type">array</span> <code class="parameter">$driver_options</code></span>
]]] )</div>
<p class="para rdfs-comment">
Creates a PDO instance to represent a connection to the requested
database.
</p>
</div>
<div class="refsect1 parameters" id="refsect1-pdo.construct-parameters">
<h3 class="title">Parameters</h3>
<p class="para">
<dl>
<dt>
<span class="term">dsn</span>
<dd>
<p class="para">
The Data Source Name, or DSN, contains the information required to
connect to the database.
</p>
<p class="para">
In general, a DSN consists of the PDO driver name, followed by a colon,
followed by the PDO driver-specific connection syntax. Further
information is available from the <a href="pdo.drivers.html" class="link">PDO
driver-specific documentation</a>.
</p>
<p class="para">
The <em><code class="parameter">dsn</code></em> parameter supports three
different methods of specifying the arguments required to create
a database connection:
</p>
<p class="para">
<dl>
<dt>
<span class="term">Driver invocation</span>
<dd>
<p class="para">
<em><code class="parameter">dsn</code></em> contains the full DSN.
</p>
</dd>
</dt>
<dt>
<span class="term">URI invocation</span>
<dd>
<p class="para">
<em><code class="parameter">dsn</code></em> consists of <strong class="userinput"><code>uri:</code></strong>
followed by a URI that defines the location of a file containing
the DSN string. The URI can specify a local file or a remote URL.
</p>
<p class="para"><strong class="userinput"><code>uri:file:///path/to/dsnfile</code></strong></p>
</dd>
</dt>
<dt>
<span class="term">Aliasing</span>
<dd>
<p class="para">
<em><code class="parameter">dsn</code></em> consists of a name
<em><code class="parameter">name</code></em> that maps to
<code class="code">pdo.dsn.<em><code class="parameter">name</code></em></code> in <var class="filename">php.ini</var>
defining the DSN string.
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
The alias must be defined in <var class="filename">php.ini</var>, and not <var class="filename">.htaccess</var> or <var class="filename">httpd.conf</var>
</p>
</p></blockquote>
</dd>
</dt>
</dl>
</p>
</dd>
</dt>
<dt>
<span class="term">username</span>
<dd>
<p class="para">
The user name for the DSN string. This parameter is optional for
some PDO drivers.
</p>
</dd>
</dt>
<dt>
<span class="term">password</span>
<dd>
<p class="para">
The password for the DSN string. This parameter is optional for
some PDO drivers.
</p>
</dd>
</dt>
<dt>
<span class="term">driver_options</span>
<dd>
<p class="para">
A key=>value array of driver-specific connection options.
</p>
</dd>
</dt>
</dl>
</p>
</div>
<div class="refsect1 returnvalues" id="refsect1-pdo.construct-returnvalues">
<h3 class="title">Return Values</h3>
<p class="para">
Returns a PDO object on success.
</p>
</div>
<div class="refsect1 errors" id="refsect1-pdo.construct-errors">
<h3 class="title">Errors/Exceptions</h3>
<p class="para">
<span class="function"><strong>PDO::__construct()</strong></span> throws a <a href="class.pdoexception.html" class="classname">PDOException</a> if the attempt
to connect to the requested database fails.
</p>
</div>
<div class="refsect1 examples" id="refsect1-pdo.construct-examples">
<h3 class="title">Examples</h3>
<p class="para">
<div class="example" id="example-918"><p><strong>Example #1 Create a PDO instance via driver invocation</strong></p>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">/* Connect to an ODBC database using driver invocation */<br /></span><span style="color: #0000BB">$dsn </span><span style="color: #007700">= </span><span style="color: #DD0000">'mysql:dbname=testdb;host=127.0.0.1'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$user </span><span style="color: #007700">= </span><span style="color: #DD0000">'dbuser'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$password </span><span style="color: #007700">= </span><span style="color: #DD0000">'dbpass'</span><span style="color: #007700">;<br /><br />try {<br /> </span><span style="color: #0000BB">$dbh </span><span style="color: #007700">= new </span><span style="color: #0000BB">PDO</span><span style="color: #007700">(</span><span style="color: #0000BB">$dsn</span><span style="color: #007700">, </span><span style="color: #0000BB">$user</span><span style="color: #007700">, </span><span style="color: #0000BB">$password</span><span style="color: #007700">);<br />} catch (</span><span style="color: #0000BB">PDOException $e</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">'Connection failed: ' </span><span style="color: #007700">. </span><span style="color: #0000BB">$e</span><span style="color: #007700">-></span><span style="color: #0000BB">getMessage</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="example" id="example-919"><p><strong>Example #2 Create a PDO instance via URI invocation</strong></p>
<div class="example-contents"><p>
The following example assumes that the file
<var class="filename">/usr/local/dbconnect</var> exists with file permissions
that enable PHP to read the file. The file contains the PDO DSN to
connect to a DB2 database through the PDO_ODBC driver:
</p></div>
<div class="example-contents screen">
<div class="cdata"><pre>
odbc:DSN=SAMPLE;UID=john;PWD=mypass
</pre></div>
</div>
<div class="example-contents"><p>
The PHP script can then create a database connection by simply
passing the <em>uri:</em> parameter and pointing to
the file URI:
</p></div>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">/* Connect to an ODBC database using driver invocation */<br /></span><span style="color: #0000BB">$dsn </span><span style="color: #007700">= </span><span style="color: #DD0000">'uri:file:///usr/local/dbconnect'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$user </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$password </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">;<br /><br />try {<br /> </span><span style="color: #0000BB">$dbh </span><span style="color: #007700">= new </span><span style="color: #0000BB">PDO</span><span style="color: #007700">(</span><span style="color: #0000BB">$dsn</span><span style="color: #007700">, </span><span style="color: #0000BB">$user</span><span style="color: #007700">, </span><span style="color: #0000BB">$password</span><span style="color: #007700">);<br />} catch (</span><span style="color: #0000BB">PDOException $e</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">'Connection failed: ' </span><span style="color: #007700">. </span><span style="color: #0000BB">$e</span><span style="color: #007700">-></span><span style="color: #0000BB">getMessage</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
<div class="example" id="example-920"><p><strong>Example #3 Create a PDO instance using an alias</strong></p>
<div class="example-contents"><p>
The following example assumes that <var class="filename">php.ini</var> contains the following
entry to enable a connection to a MySQL database using only the
alias <em>mydb</em>:
</p></div>
<div class="example-contents"><div class="inicode"><pre class="inicode">[PDO]
pdo.dsn.mydb="mysql:dbname=testdb;host=localhost"</pre>
</div></div>
<div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB"><?php<br /></span><span style="color: #FF8000">/* Connect to an ODBC database using an alias */<br /></span><span style="color: #0000BB">$dsn </span><span style="color: #007700">= </span><span style="color: #DD0000">'mydb'</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$user </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">;<br /></span><span style="color: #0000BB">$password </span><span style="color: #007700">= </span><span style="color: #DD0000">''</span><span style="color: #007700">;<br /><br />try {<br /> </span><span style="color: #0000BB">$dbh </span><span style="color: #007700">= new </span><span style="color: #0000BB">PDO</span><span style="color: #007700">(</span><span style="color: #0000BB">$dsn</span><span style="color: #007700">, </span><span style="color: #0000BB">$user</span><span style="color: #007700">, </span><span style="color: #0000BB">$password</span><span style="color: #007700">);<br />} catch (</span><span style="color: #0000BB">PDOException $e</span><span style="color: #007700">) {<br /> echo </span><span style="color: #DD0000">'Connection failed: ' </span><span style="color: #007700">. </span><span style="color: #0000BB">$e</span><span style="color: #007700">-></span><span style="color: #0000BB">getMessage</span><span style="color: #007700">();<br />}<br /><br /></span><span style="color: #0000BB">?></span>
</span>
</code></div>
</div>
</div>
</p>
<blockquote class="note"><p><strong class="note">Note</strong>:
<p class="para">
Before PHP5.3, a class which extends PDO and implements <em>__call</em> magic will always receive lower case <em><code class="parameter">$method</code></em>.
</p>
</p></blockquote>
</div>
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