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<?xml version='1.0' encoding='iso-8859-1'?>
<!-- $Revision: 1.16 $ -->
<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=>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="errors">
&reftitle.errors;
<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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