mysqli::__construct

mysqli::connect

mysqli_connect

(PHP 5, PHP 7, PHP 8)

mysqli::__construct -- mysqli::connect -- mysqli_connectAbre uma nova conexão com o servidor MySQL

Descrição

Estilo orientado à objeto

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")
)
public mysqli::connect(
    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")
): void

Estilo procedural

mysqli_connect(
    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")
): mysqli|false

Abre uma conexão com o servidor MySQL.

Parâmetros

hostname

Pode ser um nome de host ou um endereço IP. O host local é assumido ao passar o valor null ou a string "localhost" para este parâmetro. Quando possível, serão usados pipes em vez do protocolo TCP/IP. O protocolo TCP/IP é usado se um nome de host e um número de porta forem fornecidos juntos, por ex. localhost:3308.

Prepender host por p: abre uma conexão persistente. mysqli_change_user() é chamado automaticamente em conexões abertas a partir do pool de conexões.

username

O nome de usuário do MySQL.

password

Se não for fornecido ou for null, o servidor MySQL tentará autenticar o usuário apenas nos registros de usuário que não possuem senha. Isso permite que um nome de usuário seja usado com diferentes permissões (dependendo se uma senha é fornecida ou não).

database

Se fornecido, especificará o banco de dados padrão a ser usado ao realizar consultas.

port

Especifica o número da porta para tentar se conectar ao servidor MySQL.

socket

Especifica o socket ou pipe nomeado que deve ser usado.

Nota:

A especificação do parâmetro socket não determinará explicitamente o tipo de conexão a ser usada ao conectar-se ao servidor MySQL. Como a conexão é feita com o banco de dados MySQL é determinado pelo parâmetro hostname.

Valor Retornado

mysqli::__construct() sempre retorna um objeto que representa a conexão com um servidor MySQL, independente de ter sucesso ou não.

mysqli_connect() retorna um objeto que representa a conexão com um servidor MySQL, ou false em caso de falha.

mysqli::connect() retorna null no sucesso ou false em caso de falha.

Erros

Se MYSQLI_REPORT_STRICT estiver ativado e a tentativa de conexão com o banco de dados solicitado falhar, uma mysqli_sql_exception será lançada.

Exemplos

Exemplo #1 mysqli::__construct() exemplo

Estilo orientado à objeto

<?php

/* Você deve ativar o relatório de erros para mysqli antes de tentar fazer uma conexão */
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

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

/* Defina o conjunto de caracteres desejado após estabelecer uma conexão */
$mysqli->set_charset('utf8mb4');

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

Estilo procedural

<?php

/* Você deve ativar o relatório de erros para mysqli antes de tentar fazer uma conexão */
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);

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

/* Defina o conjunto de caracteres desejado após estabelecer uma conexão */
mysqli_set_charset($mysqli, 'utf8mb4');

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

Os exemplos acima irão imprimir algo similar à:

Sucesso... localhost via TCP/IP

Exemplo #2 Estendendo a classe mysqli

<?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');

Exemplo #3 Tratamento manual de erros

Se o relatório de erros estiver desabilitado, o desenvolvedor é responsável por verificar e tratar as falhas

Estilo orientado à objeto

<?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);
}

/* Defina o conjunto de caracteres desejado após estabelecer uma conexão */
$mysqli->set_charset('utf8mb4');
if (
$mysqli->errno) {
throw new
RuntimeException('mysqli error: ' . $mysqli->error);
}

Estilo procedural

<?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());
}

/* Defina o conjunto de caracteres desejado após estabelecer uma conexão */
mysqli_set_charset($mysqli, 'utf8mb4');
if (
mysqli_errno($mysqli)) {
throw new
RuntimeException('mysqli error: ' . mysqli_error($mysqli));
}

Notas

Nota:

MySQLnd sempre assume o charset padrão do banco de dados. Este charset é enviado durante a criação da conexão, e o mysqlnd usará a partir daí.

Libmysql utiliza o charset padrão configurado no arquivo my.cnf ou por uma chamada a mysqli_options() anterior a chamada de mysqli_real_connect() e depois de mysqli_init().

Nota:

Estilo orientado à objeto apenas: Se a conexão falhar, um objeto ainda será retornado. Para verificar se a conexão falhou, use a função mysqli_connect_error() ou a propriedade mysqli->connect_error como nos exemplos anteriores.

Nota:

Se for necessário definir opções, como o tempo limite de conexão, mysqli_real_connect() deve ser usado.

Nota:

Chamar o construtor sem parâmetros é o mesmo que chamar mysqli_init().

Nota:

O erro "Can't create TCP/IP socket (10106)" geralmente significa que a diretiva variables_order configure não contém o caractere E. No Windows, se o ambiente não for copiado, a variável de ambiente SYSTEMROOT não estará disponível e o PHP terá problemas ao carregar o Winsock.

Veja Também

add a note

User Contributed Notes 13 notes

up
27
fugyl13 at gmail dot com
8 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.
up
28
andres at 21brains dot com
8 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.
up
4
php at haravikk dot me
5 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.
up
6
chris at ocproducts dot com
5 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.
up
8
paul at mtnlist dot com
9 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.
up
3
PaulieG
6 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'.
up
0
arnold at nijboer dot it
1 month 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"))
up
-2
Anonymous
13 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.
up
-5
Ben
7 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();
up
-6
webmaster at aryes dot fr
7 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.
up
-6
linguafranca2003 at yahoo dot com
8 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
       
}
}
?>
up
-5
powtac at gmx de
4 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.
up
-14
oleg at mastak dot fi
9 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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