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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

## Beschreibung

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

Warnung
Diese Funktion ist EXPERIMENTELL. Das Verhalten, der Funktionsname und alles Andere was hier dokumentiert ist, kann sich in zukünftigen PHP-Versionen ohne Ankündigung ändern. Seien Sie gewarnt und verwenden Sie diese Funktion auf eigenes Risiko.

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

## Parameter Liste

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. Examples of each driver are given below:

  `PDO_DBLIB`

    The DSN prefix is either `sybase:` or `mssql:` depending on which libraries it was linked against during compilation.

    `sybase:host=localhost; dbname=testdb`

    `mssql:host=localhost; dbname=testdb`

  `PDO_FIREBIRD`

    `firebird:User=john;Password=mypass;Database=DATABASE.GDE;DataSource=localhost;Port=3050`

  `PDO_MYSQL`

    `mysql:host=localhost;dbname=testdb`

  `PDO_OCI`

    To connect via `tnsnames.ora`, use:

    `oci:mydb`

    If using instantclient, use:

    `oci:dbname=//localhost:1521/testdb`

  `PDO_ODBC`

    `odbc:DSN=SAMPLE;UID=john;PWD=mypass`

    DSN=SAMPLE refers to the SAMPLE data source configured in the ODBC driver manager.

  `PDO_PGSQL`

    `pgsql:host=localhost port=5432 dbname=testdb user=john password=mypass`

    Note, by passing user and password in the DSN, the username and password parameters become optional. If specified, they are glued to the end of the connection string.

  `PDO_SQLITE`

    `sqlite:/path/to/database`

    To create a database in memory, use:

    `sqlite::memory:`

  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.

    > Anmerkung: 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.

## Rückgabewerte

Returns a PDO object on success.

## Exceptions

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

## Beispiele

Beispiel 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(); } ?>`

Beispiel 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(); } ?>`

Beispiel 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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