mysqli __construct() Method

The mysqli::__construct() / mysqli::connect() / mysqli_connect() function is used to open a new connection to the MySQL server.

Syntax

//Object-oriented style
public mysqli::__construct(hostname, username, password, 
                           database, port, socket)
public mysqli::connect(hostname, username, password, 
                       database, port, socket)

//Procedural style
mysqli_connect(hostname, username, password, 
               database, port, socket)

Parameters

`hostname`	`Optional.` Specify the host name or an IP address. Passing the null value or "localhost" to this parameter, the local host is assumed.
`username`	`Optional.` Specify the MySQL user name.
`password`	`Optional.` Specify the MySQL password. This allows the username to be used with different permissions (depending on if a password is provided or not).
`database`	`Optional.` If provided will specify the default database to be used when performing queries.
`port`	`Optional.` Specify the port number to attempt to connect to the MySQL server.
`socket`	`Optional.` Specify the socket or named pipe that should be used.

Return Value

Returns as follows:

mysqli::__construct() always returns an object which represents the connection to a MySQL Server, regardless of it being successful or not.
mysqli_connect() returns an object which represents the connection to a MySQL Server, or false on failure.
mysqli::connect() returns null on success or false on failure.

Exceptions

If MYSQLI_REPORT_STRICT is enabled and the attempt to connect to the requested database fails, a mysqli_sql_exception is thrown.

Example: Object-oriented style

The example below shows the usage of mysqli::__construct() method.

<?php
//enabling error reporting for mysqli 
//before attempting to make a connection
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

//establishing connection to the database
$mysqli = new mysqli("localhost", "user", "password", "database");

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

The output of the above code will be similar to:

Success... localhost via TCP/IP

Example: Procedural style

The example below shows the usage of mysqli_connect() function.

<?php
//enabling error reporting for mysqli 
//before attempting to make a connection
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

//establishing connection to the database
$mysqli = mysqli_connect("localhost", "user", "password", "database");

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

The output of the above code will be similar to:

Success... localhost via TCP/IP

Example: Object-oriented style - manual error handling

If error reporting is disabled, the user is responsible for checking and handling failures. Consider the example below:

<?php
error_reporting(0);
mysqli_report(MYSQLI_REPORT_OFF);

//establishing connection to the database
$mysqli = new mysqli("localhost", "user", "password", "database");

if ($mysqli->connect_errno) {
  throw new RuntimeException('mysqli connection error: ' . $mysqli->connect_error);
}

if ($mysqli->errno) {
  throw new RuntimeException('mysqli error: ' . $mysqli->error);
}
?>

Example: Procedural style - manual error handling

Consider the example below where error is handled manually in procedural style.

<?php
error_reporting(0);
mysqli_report(MYSQLI_REPORT_OFF);

//establishing connection to the database
$mysqli = mysqli_connect("localhost", "user", "password", "database");

if (mysqli_connect_errno()) {
  throw new RuntimeException('mysqli connection error: ' . mysqli_connect_error());
}

if (mysqli_errno($mysqli)) {
  throw new RuntimeException('mysqli error: ' . mysqli_error($mysqli));
}
?>

❮ MySQLi Functions Reference