mysqli::__construct

mysqli::connect

mysqli_connect

(PHP 5, PHP 7, PHP 8)

mysqli::__construct -- mysqli::connect -- mysqli_connect — 新規に MySQL サーバーへの接続をオープンする

説明

オブジェクト指向型

public mysqli::__construct(
    ?string $hostname = null,
    ?string $username = null,
    ?string $password = null,
    ?string $database = null,
    ?int $port = null,
    ?string $socket = null
)

public mysqli::connect(
    ?string $hostname = null,
    ?string $username = null,
    ?string $password = null,
    ?string $database = null,
    ?int $port = null,
    ?string $socket = null
): bool

手続き型

mysqli_connect(
    ?string $hostname = null,
    ?string $username = null,
    ?string $password = null,
    ?string $database = null,
    ?int $port = null,
    ?string $socket = null
): mysqli|false

MySQL サーバーへの接続をオープンします。

パラメータ

hostname

ホスト名または IP アドレスです。この引数に null を渡すと mysqli.default_host から値を取得します。可能な場合は、TCP/IP プロトコルの代わりにパイプが使用されます。ホスト名とポートが一緒に指定された場合は、TCP/IP プロトコルが使われます。例: localhost:3308.

ホストの前に p: をつけると、持続的な接続を開きます。接続プールから開いた接続上で mysqli_change_user() が自動的にコールされます。

username

MySQL のユーザー名。 null の場合は、mysqli.default_user iniオプションに基づいてユーザー名が決定されます。

password

MySQL のパスワード。 null の場合は、mysqli.default_pw iniオプションに基づいてパスワードが決定されます。

database

null 以外を指定した場合は、クエリが実行されるデフォルトのデータベースとなります。

port

MySQL サーバーに接続する際のポート番号を指定します。 null の場合は、mysqli.default_port iniオプションに基づいてポート番号が決定されます。

socket

使用するソケットあるいは名前つきパイプを指定します。 null の場合は、mysqli.default_socket iniオプションに基づいてソケットが決定されます。

注意:
socket 引数を指定しても、MySQL サーバーへの接続時の型を明示的に定義することにはなりません。MySQL サーバーへの接続方法については hostname 引数で定義されます。

戻り値

mysqli_connect() は、 MySQL サーバーへの接続を表すオブジェクトを返します。失敗した場合に false を返します.

mysqli::connect() は、成功した場合に true を返します。失敗した場合に null を返します。

エラー / 例外

mysqli のエラー報告 (MYSQLI_REPORT_ERROR) が有効になっており、かつ要求された操作が失敗した場合は、警告が発生します。さらに、エラー報告のモードが MYSQLI_REPORT_STRICT に設定されていた場合は、mysqli_sql_exception が代わりにスローされます。

変更履歴

バージョン	説明
8.1.0	mysqli::connect() は、成功時に `null` ではなく `true` を返すようになりました。
7.4.0	すべてのパラメータが、nullable になりました。

例

例1 mysqli::__construct() の例

オブジェクト指向型

<?php

/* You should enable error reporting for mysqli before attempting to make a connection */
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

$mysqli = new mysqli('localhost', 'my_user', 'my_password', 'my_db');

/* Set the desired charset after establishing a connection */
$mysqli->set_charset('utf8mb4');

printf("Success... %s\n", $mysqli->host_info);

手続き型

<?php

/* You should enable error reporting for mysqli before attempting to make a connection */
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

$mysqli = mysqli_connect('localhost', 'my_user', 'my_password', 'my_db');

/* Set the desired charset after establishing a connection */
mysqli_set_charset($mysqli, 'utf8mb4');

printf("Success... %s\n", mysqli_get_host_info($mysqli));

上の例の出力は、たとえば以下のようになります。

Success... localhost via TCP/IP

例2 mysqli クラスを拡張する

<?php

class FooMysqli extends mysqli {
    public function __construct($host, $user, $pass, $db, $port, $socket, $charset) {
        mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
        parent::__construct($host, $user, $pass, $db, $port, $socket);
        $this->set_charset($charset);
    }
}

$db = new FooMysqli('localhost', 'my_user', 'my_password', 'my_db', 3306, null, 'utf8mb4');

例3 手動によるエラーハンドリング

エラーの報告機能が無効になっている場合、開発者がエラーのチェックとエラー処理を行う必要があります。

オブジェクト指向型

<?php

error_reporting(0);
mysqli_report(MYSQLI_REPORT_OFF);
$mysqli = new mysqli('localhost', 'my_user', 'my_password', 'my_db');
if ($mysqli->connect_errno) {
    throw new RuntimeException('mysqli connection error: ' . $mysqli->connect_error);
}

/* Set the desired charset after establishing a connection */
$mysqli->set_charset('utf8mb4');
if ($mysqli->errno) {
    throw new RuntimeException('mysqli error: ' . $mysqli->error);
}

手続き型

<?php

error_reporting(0);
mysqli_report(MYSQLI_REPORT_OFF);
$mysqli = mysqli_connect('localhost', 'my_user', 'my_password', 'my_db');
if (mysqli_connect_errno()) {
    throw new RuntimeException('mysqli connection error: ' . mysqli_connect_error());
}

/* Set the desired charset after establishing a connection */
mysqli_set_charset($mysqli, 'utf8mb4');
if (mysqli_errno($mysqli)) {
    throw new RuntimeException('mysqli error: ' . mysqli_error($mysqli));
}

注意

注意:
MySQLnd は常に、サーバーのデフォルト文字セットを想定しています。この文字セットは接続時のハンドシェイク/認証のときに送信され、これを mysqlnd が使います。

Libmysqlclient が使うデフォルトの文字セットは my.cnf で設定したものです。あるいは明示的に mysqli_options() をコールして設定することもできます。これは、mysqli_init() のあとで mysqli_real_connect() を実行する前にコールします。

注意:
オブジェクト指向型に関する注意: 接続に失敗した場合にもオブジェクトが返されます。接続が失敗したかどうかを確かめるには、先ほどの例のように mysqli_connect_error() 関数あるいは mysqli->connect_error プロパティを使用しましょう。

注意:
接続タイムアウトなどのオプションを設定する必要がある場合は、かわりに mysqli_real_connect() を使わなければなりません。

注意:
コンストラクタをパラメータなしでコールするのは、 mysqli_init() をコールするのと同じ意味になります。

注意:
エラー "Can't create TCP/IP socket (10106)" が発生するのは、たいていは variables_order 設定ディレクティブに E が含まれていない場合です。 Windows では、これが含まれていなければ SYSTEMROOT 環境変数が使用できず、PHP が Winsock の読み込みに失敗します。

参考

mysqli_real_connect() - mysql サーバーとの接続をオープンする
mysqli_options() - オプションを設定する
mysqli_connect_errno() - 直近の接続コールに関するエラーコードを返す
mysqli_connect_error() - 直近の接続エラーの説明を返す
mysqli_close() - 事前にオープンしているデータベース接続を閉じる

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User Contributed Notes 13 notes

down

fugyl13 at gmail dot com ¶

10 years ago


Note that on all >=Windows 7 Servers, a host name "localhost" will create a very expensive lookup (~1 Second). 

That's because since Windows 7, the hosts file doesn't come with a preconfigured
127.0.0.1 localhost
anymore

So, if you notice a long connection creation, try "127.0.0.1" instead.

down

andres at 21brains dot com ¶

10 years ago


Please do use set_charset("utf8") after establishing the connection if you want to avoid weird string issues. I do not know why the documentation does not warn you about this kind of stuff.

We had a hard time figuring out what was going on since we were using mb_detect_encoding and it said everything was UTF-8, but of course the display was wrong. If we used iconv from ISO-8859-1 to UTF-8 the strings looked fine, even though everything in the database had the right collation. So in the end, it was the connection that was the filter and although the notes for this function mention default charsets, it almost reads as a sidenote instead of a central issue when dealing with UTF and PHP/MySQL.

down

php at haravikk dot me ¶

7 years ago


Just wanted to add a note for anyone looking to use the MySQLi persistent connections feature; it's important to note that PHP opens and retains one connection per database user per process.

What this means is that if you are hosting multiple applications, each with its own database user (as is good practice) then you will end up multiplying the number of connections that PHP may hold open.

For example, if you have PHP configured with a maximum of eight worker processes, and you regularly use four different database users, then your MySQL server will need to accept at LEAST a maximum of 32 connections, or else it will run out.

However, if you would like to minimise the number of connections, what you can do is instead is to open the connection using a "guest" user (with no privileges except logging in) and then use ->change_user() to switch to a more privileged user, before switching back to the guest when you're done. Since all of the connections would therefore belong to the guest user, PHP should only maintain one per worker process.

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chris at ocproducts dot com ¶

7 years ago


There's a separate port parameter, unlike mysql_connect. However, using host:port on the host parameter does actually work.

There is a caveat. If the host is 'localhost' then the port is ignored, whether you use a port parameter or the implicit syntax I mentioned above. This is because 'localhost' will make it use unix sockets rather than TCP/IP.

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paul at mtnlist dot com ¶

11 years ago


If you want to connect via an alternate port (other than 3306), as you might when using an ssh tunnel to another host, using "localhost" as the hostname will not work. 

Using 127.0.0.1 will work.  Apparently, if you specify the host as "localhost", the constructor ignores the port specified as an argument to the constructor.

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PaulieG ¶

8 years ago


It should be noted that on PHP 7 (v7.0.2 at least), passing the empty string '' for the Port argument while connecting to 'localhost' will prevent the connection from being successful altogether.

To work around this, use 'null'.

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arnold at nijboer dot it ¶

1 year ago


public mysqli::__construct(
    string $hostname = ini_get("mysqli.default_host"),
    string $username = ini_get("mysqli.default_user"),
    string $password = ini_get("mysqli.default_pw"),
    string $database = "",
    int $port = ini_get("mysqli.default_port"),
    string $socket = ini_get("mysqli.default_socket")
)

the mysqli construct looks at the Master PHP.ini values.
if you're using a local ini overwrite of some sort add the ini_get to you're php script:
$mysqli = new mysqli(ini_get("mysqli.default_host"),ini_get("mysqli.default_user"),ini_get("mysqli.default_pw"))

down

-2

Anonymous ¶

15 years ago


If you get an error like 

  Can't connect to MySQL server on 'localhost' (10061)

and you use named pipes/socket connections (or aren't sure how you installed the MySQL server) try the following connect command:



<?php

mysqli_connect('.', $user_name, $password, $database_name, null, 'mysql');

?>



The '.' as hostname is absolutely necessary when using named pipes. 'localhost' won't work. 'mysql' is the standard name for the pipe/socket.

down

-6

Ben ¶

9 years ago


A far more secure and language independent way of connecting to mysql is to use the READ_DEFAULT_FILE options. This passes the workload over to the mysql library, which allows for the configuration file itself to be outside of the scope of the language.

The config file itself is something like this:
[client]
user=user_u
password=user_password
host=dbhost
port=3306
database=the_database
default-character-set=utf8

The following code fragment (in OO mysql_i format)

$sqlconf='/var/private/my.cnf';
$sql = new mysqli;
$sql->init();
$sql->options(MYSQLI_READ_DEFAULT_FILE,$sqlconf);
$sql->real_connect();

down

-6

linguafranca2003 at yahoo dot com ¶

9 years ago


mysqli can succeed in surprising ways, depending on the privileges granted to the user. For example,

GRANT USAGE ON *.* TO 'myuser'@'localhost' IDENTIFIED BY PASSWORD 'mypassword';
GRANT ALL PRIVILEGES ON `database_a`.* TO 'myuser'@'localhost';
CREATE DATABASE database_b;

<?php
$db = new mysqli('localhost', 'myuser', 'mypassword', 'database_b');

if ($db->connect_error) {
        die('Connect Error (' . $db->connect_errno . ') '
            . $mysqli->connect_error);
}

printf("SQLSTATE: %s\n", $this->db->sqlstate);
printf("Warning Count: %s\n", $db->warning_count);
$db->close();
?>

Will output:

SQLSTATE: 00000 
Warning Count: 0

So, life is good — you're connected to the database and executing mysqli methods. Except, life isn't good, because you aren't actually using database_b because myuser doesn't have any privileges on it. You won't catch this until you try to perform a later operation, when you'll get an error, "MYSQL Error: No database selected", and find yourself scratching your head and thinking "what do you mean, of course I have a database selected; I selected one when I called the constructor".

As a result, you may want to perform an additional check after connecting to mysql, to confirm that you're actually connected not just to the mysql server, but to the actual database:

<?php
$db = new mysqli('localhost', 'myuser', 'mypassword', 'database_b');

if ($db->connect_error) {
        die('Connect Error (' . $db->connect_errno . ') '
            . $mysqli->connect_error);
} elseif ($result = $db->query("SELECT DATABASE()")) {
        $row = $result->fetch_row();
        if ($row[0] != 'database_b') {
                //oops! We're connected to mysql, but not to database_b
        }
}
?>

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-7

webmaster at aryes dot fr ¶

9 years ago


A friend of mine encountered a sudden bug with CMS Piwigo. I discovered that :
- He had a hosting rule to use PHP 5.6.
- The hoster uses 5.6.6, verified using phpinfo();.
- The CMS declared a database name parameter as null.

That gallery CMS was unable to connect to MySQL and left only a warning message about it.

We tried to revert back to PHP 5.5, the CMS worked again.

Then we switched back to 5.6.6 and changed those lines :

  $dbname = null;
  
  $mysqli = new mysqli($host, $user, $password, $dbname, $port, $socket);

to

  $dbname = ''; // Use an empty string, not null
  
  $mysqli = new mysqli($host, $user, $password, $dbname, $port, $socket);

It worked!

So if you made the same mistake, using null where the manual invites to use an empty string, you should consider correcting your code.

down

-4

powtac at gmx de ¶

6 years ago


Be careful, mysqli_connect() does not return a resource ! It returns an instance of the mysqli class (http://php.net/manual/class.mysqli.php) The old mysql_connect() function did return a resource.

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-14

oleg at mastak dot fi ¶

11 years ago


If you want to connect to local named pipe on windows and you get error "php_network_getaddresses: getaddrinfo failed: No such host is known. ", even if you using using "." as host, please check your if you are using mysqlnd driver: If this is true, then probably you need to update to version 5.4 of php:

Named pipes support for Windows was added in PHP version 5.4.0.
@ http://php.net/manual/en/mysqlnd.overview.php 

Hopefully that will save you some time.

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