(PHP 5, PHP 7, PHP 8)
mysqli::__construct -- mysqli::connect -- mysqli_connect — Open a new connection to the MySQL server
Stile orientato agli oggetti
$hostname = null,$username = null,$password = null,$database = null,$port = null,$socket = null$hostname = null,$username = null,$password = null,$database = null,$port = null,$socket = nullStile procedurale
$hostname = null,$username = null,$password = null,$database = null,$port = null,$socket = nullOpens a connection to the MySQL Server.
hostname
Can be either a host name or an IP address. When passing null, the value is retrieved from
mysqli.default_host.
When possible, pipes will be used instead of the TCP/IP protocol.
The TCP/IP protocol is used if a host name and port number are provided together e.g. localhost:3308.
Prepending host by p: opens a persistent connection.
mysqli_change_user() is automatically called on
connections opened from the connection pool.
username
The MySQL username or null to assume the username based on the
mysqli.default_user ini option.
password
The MySQL password or null to assume the password based on the
mysqli.default_pw ini option.
database
The default database to be used when performing queries or null.
port
The port number to attempt to connect to the MySQL server or null to assume the port based on the
mysqli.default_port ini option.
socket
The socket or named pipe that should be used or null to assume the socket based on the
mysqli.default_socket ini option.
Nota:
Specifying the
socketparameter will not explicitly determine the type of connection to be used when connecting to the MySQL server. How the connection is made to the MySQL database is determined by thehostnameparameter.
mysqli_connect() returns an object which represents the connection to a MySQL Server,
o false in caso di fallimento.
mysqli::connect() returns true on success o false in caso di fallimento.
Prior to PHP 8.1.0, returns null on success.
If mysqli error reporting is enabled (MYSQLI_REPORT_ERROR) and the requested operation fails,
a warning is generated. If, in addition, the mode is set to MYSQLI_REPORT_STRICT,
a mysqli_sql_exception is thrown instead.
| Versione | Descrizione |
|---|---|
| 8.1.0 |
mysqli::connect() now returns true instead of null on success.
|
| 7.4.0 | All parameters are now nullable. |
Example #1 mysqli::__construct() example
Stile orientato agli oggetti
<?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);Stile procedurale
<?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($mysqli));The above examples will output something similar to:
Success... localhost via TCP/IP
Example #2 Extending mysqli class
<?php
class FooMysqli extends mysqli {
public function __construct($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');Example #3 Manual error handling
If error reporting is disabled, the developer is responsible for checking and handling failures
Stile orientato agli oggetti
<?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);
}Stile procedurale
<?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));
}Nota:
MySQLnd utilizza sempre il set di caratteri di default del sistema. Questo set di caratteri è inviato durante l'handshaking/autenticazione alla connessione.
Libmysqlclient usa il set di caratteri di default impostato nel file my.cnf o attraverso una chiamata esplicita a mysqli_options() prima di chiamare mysqli_real_connect(), ma dopo mysqli_init().
Nota:
Stile orientato agli oggetti only: If the connection fails, an object is still returned. To check whether the connection failed, use either the mysqli_connect_error() function or the mysqli->connect_error property as in the preceding examples.
Nota:
If it is necessary to set options, such as the connection timeout, mysqli_real_connect() must be used instead.
Nota:
Calling the constructor with no parameters is the same as calling mysqli_init().
Nota:
Error "Can't create TCP/IP socket (10106)" usually means that the variables_order configure directive doesn't contain character
E. On Windows, if the environment is not copied theSYSTEMROOTenvironment variable won't be available and PHP will have problems loading Winsock.
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.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.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.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.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.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"))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'.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.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();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.