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

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  <refentry id="function.PDO-construct">
   <refnamediv>
    <refname>PDO::__construct</refname>
    <refpurpose>
     Creates a PDO instance to represent a connection to a database
    </refpurpose>
   </refnamediv>
   <refsect1>
    <title>Description</title>
    <methodsynopsis>
     <type>PDO</type><methodname>PDO::__construct</methodname>
     <methodparam><type>string</type><parameter>dsn</parameter></methodparam>
     <methodparam><type>string</type><parameter>username</parameter></methodparam>
     <methodparam><type>string</type><parameter>password</parameter></methodparam>
     <methodparam choice="opt"><type>array</type><parameter>driver_opts</parameter></methodparam>
    </methodsynopsis>
    &warn.experimental.func;
    <para>
     Creates a PDO instance to represent a connection to the requested
     database. The <parameter>dsn</parameter> parameter supports three
     different methods of specifying the arguments required to create
     a database connection:
     <variablelist>
      <varlistentry><term>Driver invocation</term>
       <listitem>
        <para>
         <parameter>dsn</parameter> consists of the PDO driver name, followed
         by a colon, followed by the PDO driver-specific connection syntax.
         For example, <userinput>'odbc:DSN=SAMPLE;UID=db2inst1;PWD=ibmdb2'</userinput>
         would create a PDO_ODBC connection to an ODBC database, while
         <userinput>'mysql:host=127.0.0.1;dbname=testdb'</userinput> would create
         a PDO_MYSQL connection to a MySQL database.
        </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>
       </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. <parameter>name</parameter> can not contain
         a colon.
        </para>
       </listitem>
      </varlistentry>
     </variablelist>
     If <parameter>username</parameter> or <parameter>password</parameter>
     are not required to complete the connection, you must pass empty strings
     or the constructor will throw a PDOException exception.
    </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>
     <programlisting>
<![CDATA[
odbc:DSN=SAMPLE;UID=db2inst1;PWD=password
]]>
     </programlisting>
     <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>:
      <screen>pdo.dsn.mydb=mysql:dbname=testdb;host=127.0.0.1</screen>
     </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>
   </refsect1>
  </refentry>

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