mysqli::__construct

mysqli_connect

(PHP 5, PHP 7, PHP 8)

mysqli::__construct -- mysqli_connect — Abre una nueva conexión al servidor de MySQL

Descripción

Estilo orientado a objetos

mysqli::__construct(
    string $host = ini_get("mysqli.default_host"),
    string $username = ini_get("mysqli.default_user"),
    string $passwd = ini_get("mysqli.default_pw"),
    string $dbname = "",
    int $port = ini_get("mysqli.default_port"),
    string $socket = ini_get("mysqli.default_socket")
)

Estilo por procedimientos

mysqli_connect(
    string $host = ini_get("mysqli.default_host"),
    string $username = ini_get("mysqli.default_user"),
    string $passwd = ini_get("mysqli.default_pw"),
    string $dbname = "",
    int $port = ini_get("mysqli.default_port"),
    string $socket = ini_get("mysqli.default_socket")
): mysqli

Abre una conexión al Servidor de MySQL que está en ejecución.

Parámetros

host

Puede ser o un nombre de host o una dirección IP. Pasando el valor null o la cadena "localhost" a este parámetro, se asumirá el host local. Cuando es posible, se usarán tuberías en lugar del protocolo TCP/IP.

Anteponer p: al host, abre una conexión persistente. mysqli_change_user() es automáticamente llamado en conexiones abiertas desde la caché de conexiones.

username

El nombre de usuario de MySQL.

passwd

Si no se proporciona o es null, el servidor MySQL intentará autentificar el usuario solo con aquellos registros de usuarios que no tienen contraseña. Esto permite que un nombre de usuario ser usado con diferentes permisos (dependiendo de si se proporciona una contraseña o no).

dbname

Si se proporcioina, especificará la base de datos prederminada a usar cuando se realizan consultas.

port

Especifica el número al que intentar conectar al servidor de MySQL.

socket

Especifica el socket o la tubería con nombre que debería usarse.

Nota:
Especificar el parámetro socket no determinará explicitamente el tipo de conexión a utilizar cuando se conecte al servidor MySQL. El modo de realizar la conexión a la base de datos MySQL es determinado por el parámetro host.

Valores devueltos

Devuelve un objeto que representa la conexión al servidor MySQL.

Historial de cambios

Versión	Descripción
5.3.0	Se añadió la capacidad de conexiones persistentes.

Ejemplos

Ejemplo #1 Ejemplo de mysqli::__construct()

Estilo orientado a objetos

<?php
$mysqli = new mysqli('localhost', 'mi_usuario', 'mi_contraseña', 'mi_bd');

/*
 * Esta es la forma OO "oficial" de hacerlo,
 * AUNQUE $connect_error estaba averiado hasta PHP 5.2.9 y 5.3.0.
 */
if ($mysqli->connect_error) {
    die('Error de Conexión (' . $mysqli->connect_errno . ') '
            . $mysqli->connect_error);
}

/*
 * Use esto en lugar de $connect_error si necesita asegurarse
 * de la compatibilidad con versiones de PHP anteriores a 5.2.9 y 5.3.0.
 */
if (mysqli_connect_error()) {
    die('Error de Conexión (' . mysqli_connect_errno() . ') '
            . mysqli_connect_error());
}

echo 'Éxito... ' . $mysqli->host_info . "\n";

$mysqli->close();
?>

Estilo orientado a objetos cuando se extiende la clase mysqli

<?php

class foo_mysqli extends mysqli {
    public function __construct($host, $usuario, $contraseña, $bd) {
        parent::__construct($host, $usuario, $contraseña, $bd);

        if (mysqli_connect_error()) {
            die('Error de Conexión (' . mysqli_connect_errno() . ') '
                    . mysqli_connect_error());
        }
    }
}

$bd = new foo_mysqli('localhost', 'mi_usuario', 'mi_contraseña', 'mi_bd');

echo 'Éxito... ' . $bd->host_info . "\n";

$bd->close();
?>

Estilo por procedimientos

<?php
$enlace = mysqli_connect('localhost', 'mi_usuario', 'mi_contraseña', 'mi_bd');

if (!$enlace) {
    die('Error de Conexión (' . mysqli_connect_errno() . ') '
            . mysqli_connect_error());
}

echo 'Éxito... ' . mysqli_get_host_info($enlace) . "\n";

mysqli_close($enlace);
?>

El resultado de los ejemplos sería:

Éxito... MySQL host info: localhost via TCP/IP

Notas

Nota:
MySQLnd siempre utiliza el juego de caracteres de idioma predeterminado. El juego de caracteres se envía en la autentificación/acuerdo que se produce durante la conexión, que utilizará mysqlnd.
Libmysqlclient utiliza el juego de caracteres predeterminado definido en my.cnf o se puede establecer llamando mysqli_options() antes de user mysqli_real_connect(), pero después de mysqli_init().

Nota:
Sólo para la sintaxis OO: Si una conexión falla se devuelve un objeto. Para comprobar si la conexión falló, use la función mysqli_connect_error() o la propiedad mysqli->connect_error como en los ejemplos anteriores.

Nota:
Si es necesario establecer las opciones, tales como el tiempo de espera de conexión, se debe utilizar mysqli_real_connect() en su lugar.

Nota:
Llamar al constructor sin parámetros es lo mismo que llamar a la función mysqli_init().

Nota:
El error "Can't create TCP/IP socket (10106)" normalmente significa que la directiva de configuración variables_order no contiene el carácter E. En Windows, si el entorno no es copiado, la variable de entorno SYSTEMROOT no estará disponible y PHP tendrá problemas al cargar Winsock.

Ver también

mysqli_real_connect() - Abre una conexión a un servidor mysql
mysqli_options() - Establecer opciones
mysqli_connect_errno() - Devuelve el código de error de la última llamada
mysqli_connect_error() - Devuelve una cadena con la descripción del último error de conexión
mysqli_close() - Cierra una conexión previamente abierta a una base de datos

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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"))

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-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.

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-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();

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-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.

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-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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