php-doc-en/reference/pdo/functions/PDO-construct.xml

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<!-- $Revision: 1.15 $ -->
  <refentry id="function.PDO-construct">
   <refnamediv>
    <refname>PDO::__construct</refname>
    <refpurpose>
     Creates a PDO instance representing a connection to a database
    </refpurpose>
   </refnamediv>
   <refsect1 role="description">
    &reftitle.description;
    <methodsynopsis>
     <type>PDO</type><methodname>PDO::__construct</methodname>
     <methodparam><type>string</type><parameter>dsn</parameter></methodparam>
     <methodparam choice="opt"><type>string</type><parameter>username</parameter></methodparam>
     <methodparam choice="opt"><type>string</type><parameter>password</parameter></methodparam>
     <methodparam choice="opt"><type>array</type><parameter>driver_options</parameter></methodparam>
    </methodsynopsis>
    <para>
     Creates a PDO instance to represent a connection to the requested
     database. 
    </para>
   </refsect1>
   <refsect1 role="parameters">
    &reftitle.parameters;
    <para>
     <variablelist>
      <varlistentry><term>dsn</term>
       <listitem>
        <para>
         The Data Source Name, or DSN, contains the information required to
         connect to the database.
        </para>
        <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 <link linkend="pdo.drivers">PDO
         driver-specific documentation</link>.
        </para>
        <para>
         The <parameter>dsn</parameter> parameter supports three
         different methods of specifying the arguments required to create
         a database connection:
        </para>
        <para>
         <variablelist>
          <varlistentry><term>Driver invocation</term>
           <listitem>
            <para>
             <parameter>dsn</parameter> contains the full DSN.
            </para>
           </listitem>
          </varlistentry>
          <varlistentry><term>URI invocation</term>
           <listitem>
            <para>
             <parameter>dsn</parameter> consists of <userinput>uri:</userinput>
             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.
            </para>
            <para><userinput>uri:file:///path/to/dsnfile</userinput></para>
           </listitem>
          </varlistentry>
          <varlistentry><term>Aliasing</term>
           <listitem>
            <para>
             <parameter>dsn</parameter> consists of a name 
             <parameter>name</parameter> that maps to 
             <literal>pdo.dsn.<parameter>name</parameter></literal> in &php.ini;
             defining the DSN string.
            </para>
            <note>
             <para>
              The alias must be defined in &php.ini;, and not &htaccess; or &httpd.conf;
             </para>
            </note>
           </listitem>
          </varlistentry>
         </variablelist>
        </para>
       </listitem>
      </varlistentry>
      <varlistentry><term>username</term>
       <listitem>
        <para>
         The user name for the DSN string. This parameter is optional for
         some PDO drivers.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry><term>password</term>
       <listitem>
        <para>
         The password for the DSN string. This parameter is optional for
         some PDO drivers.
        </para>
       </listitem>
      </varlistentry>
      <varlistentry><term>driver_options</term>
       <listitem>
        <para>
         A key=&gt;value array of driver-specific connection options.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
    </para>
   </refsect1>

   <refsect1 role="returnvalues">
    &reftitle.returnvalues;
    <para>
     Returns a PDO object on success.
    </para>
   </refsect1>

   <refsect1 role="exceptions">
    &reftitle.exceptions;
    <para>
     <function>PDO::construct</function> throws a PDOException if the attempt
     to connect to the requested database fails.
    </para>
   </refsect1>

   <refsect1 role="examples">
    &reftitle.examples;
    <para>
     <example><title>Create a PDO instance via driver invocation</title>
      <programlisting role="php">
<![CDATA[
<?php
/* Connect to an ODBC database using driver invocation */
$dsn = 'mysql:dbname=testdb;host=127.0.0.1';
$user = 'dbuser';
$password = 'dbpass';

try {
    $dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

?>
]]>
      </programlisting>
     </example>
     <example><title>Create a PDO instance via URI invocation</title>
      <para>
       The following example assumes that the file
       <filename>/usr/local/dbconnect</filename> 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:
      </para>
      <screen>
<![CDATA[
odbc:DSN=SAMPLE;UID=john;PWD=mypass
]]>
      </screen>
      <para>
       The PHP script can then create a database connection by simply
       passing the <literal>uri:</literal> parameter and pointing to
       the file URI:
      </para>
      <programlisting role="php">
<![CDATA[
<?php
/* Connect to an ODBC database using driver invocation */
$dsn = 'uri:file:///usr/local/dbconnect';
$user = '';
$password = '';

try {
    $dbh = new PDO($dsn, $user, $password);
} catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

?>
]]>
      </programlisting>
     </example>
     <example><title>Create a PDO instance using an alias</title>
      <para>
       The following example assumes that &php.ini; contains the following
       entry to enable a connection to a MySQL database using only the
       alias <literal>mydb</literal>:
       <programlisting role="ini">
[PDO]
pdo.dsn.mydb="mysql:dbname=testdb;host=localhost"
       </programlisting>
      </para>
      <programlisting role="php">
<![CDATA[
<?php
/* Connect to an ODBC database using an alias */
$dsn = 'mydb';
$user = '';
$password = '';

try {
    $dbh = new PDO($dsn, $user, $password);
}catch (PDOException $e) {
    echo 'Connection failed: ' . $e->getMessage();
}

?>
]]>
      </programlisting>
     </example>
    </para>
   </refsect1>
  </refentry>

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