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# PDO::__construct

(no version information, might be only in CVS)

PDO::__construct -- Creates a PDO instance representing a connection to a database

## Description

PDO PDO::__construct ( string dsn [, string username [, string password [, array driver_options]]] )

Creates a PDO instance to represent a connection to the requested database.

## Parameters

dsn

  The Data Source Name, or DSN, contains the information required to connect to the database.

  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 PDO driver-specific documentation.

  The dsn parameter supports three different methods of specifying the arguments required to create a database connection:

  Driver invocation

    dsn contains the full DSN.

  URI invocation

    dsn consists of `uri:` 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.

    `uri:file:///path/to/dsnfile`

  Aliasing

    dsn consists of a name name that maps to pdo.dsn.name in `php.ini` defining the DSN string.

    > Note: The alias must be defined in `php.ini`, and not `.htaccess` or `httpd.conf`

username

  The user name for the DSN string. This parameter is optional for some PDO drivers.

password

  The password for the DSN string. This parameter is optional for some PDO drivers.

driver_options

  A key=>value array of driver-specific connection options.

## Return Values

Returns a PDO object on success.

## Exceptions

PDO::construct() throws a PDOException if the attempt to connect to the requested database fails.

## Examples

Example 1. Create a PDO instance via driver invocation
`<?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(); } ?>`

Example 2. Create a PDO instance via URI invocation The following example assumes that the file `/usr/local/dbconnect` 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:
    odbc:DSN=SAMPLE;UID=john;PWD=mypass
The PHP script can then create a database connection by simply passing the uri: parameter and pointing to the file URI:
`<?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(); } ?>`

Example 3. Create a PDO instance using an alias The following example assumes that `php.ini` contains the following entry to enable a connection to a MySQL database using only the alias mydb:
    [PDO]
    pdo.dsn.mydb="mysql:dbname=testdb;host=localhost"
`<?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(); } ?>`

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