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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]]] )

警告
這個函數是實驗性質的。這個函數的行為、名稱、和關於此函數的任何其他文件在未來PHP的發行中可能會在不通知的情況下改變。 使用此延伸需自行承擔風險。

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

## Parameters

dsn

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

  Driver invocation

    dsn consists of the PDO driver name, followed by a colon, followed by the PDO driver-specific connection syntax. For example, `'odbc:DSN=SAMPLE;UID=db2inst1;PWD=ibmdb2'` would create a PDO_ODBC connection to an ODBC database, while `'mysql:host=127.0.0.1;dbname=testdb'` would create a PDO_MYSQL connection to a MySQL database.

  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.

  Aliasing

    dsn consists of a name name that maps to pdo.dsn.name in `php.ini` defining the DSN string. name can not contain a colon.

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.

## 範例

範例 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(); } ?>`

範例 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=db2inst1;PWD=password

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(); } ?>`

範例 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.dsn.mydb=mysql:dbname=testdb;host=127.0.0.1

`<?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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