文字

mysqli::__construct

mysqli_connect

(PHP 5)

mysqli::__construct -- mysqli_connectOpen a new connection to the MySQL server

说明

面向对象风格

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") ]]]]]] )

过程化风格

mysqli 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") ]]]]]] )

Opens a connection to the MySQL Server running on.

参数

host

Can be either a host name or an IP address. Passing the NULL value or the string "localhost" to this parameter, the local host is assumed. When possible, pipes will be used instead of the TCP/IP protocol.

Prepending host by p: opens a persistent connection. mysqli_change_user() is automatically called on connections opened from the connection pool.

username

The MySQL user name.

passwd

If not provided or NULL , the MySQL server will attempt to authenticate the user against those user records which have no password only. This allows one username to be used with different permissions (depending on if a password as provided or not).

dbname

If provided will specify the default database to be used when performing queries.

port

Specifies the port number to attempt to connect to the MySQL server.

socket

Specifies the socket or named pipe that should be used.

Note:

Specifying the socket parameter 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 the host parameter.

返回值

Returns an object which represents the connection to a MySQL Server.

更新日志

版本 说明
5.3.0 Added the ability of persistent connections.

范例

Example #1 mysqli::__construct() example

面向对象风格

<?php
$mysqli 
= new  mysqli ( 'localhost' 'my_user' 'my_password' 'my_db' );


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


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

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

$mysqli -> close ();
?>

面向对象风格 when extending mysqli class

<?php

class  foo_mysqli  extends  mysqli  {
    public function 
__construct ( $host $user $pass $db ) {
        
parent :: __construct ( $host $user $pass $db );

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

$db  = new  foo_mysqli ( 'localhost' 'my_user' 'my_password' 'my_db' );

echo 
'Success... '  $db -> host_info  "\n" ;

$db -> close ();
?>

过程化风格

<?php
$link 
mysqli_connect ( 'localhost' 'my_user' 'my_password' 'my_db' );

if (!
$link ) {
    die(
'Connect Error ('  mysqli_connect_errno () .  ') '
            
mysqli_connect_error ());
}

echo 
'Success... '  mysqli_get_host_info ( $link ) .  "\n" ;

mysqli_close ( $link );
?>

以上例程会输出:

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

注释

Note:

MySQLnd 总是使用服务器的默认字符集。此字符集在连接握手/认证时发送,并被 mysqlnd 使用。

Libmysqlclient 使用 my.cnf 中的默认字符集或者由在调用 mysqli_init() 之后, mysqli_real_connect() 之前先调用 mysqli_options() 来指定。

Note:

OO syntax only: If a connection fails an object is still returned. To check if the connection failed then use either the mysqli_connect_error() function or the mysqli->connect_error property as in the preceding examples.

Note:

If it is necessary to set options, such as the connection timeout, mysqli_real_connect() must be used instead.

Note:

Calling the constructor with no parameters is the same as calling mysqli_init() .

Note:

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 the SYSTEMROOT environment variable won't be available and PHP will have problems loading Winsock.

参见

  • mysqli_real_connect() - 建立一个 MySQL 服务器连接
  • mysqli_options() - Set options
  • mysqli_connect_errno() - Returns the error code from last connect call
  • mysqli_connect_error() - Returns a string description of the last connect error
  • mysqli_close() - 关闭先前打开的数据库连接

用户评论:

[#1] till at etill dot net [2015-11-18 21:08:48]

Note that if the host name is an empty string, like so:

<?php
    mysqli
'''user''password''database');
?>


then the object returned will have connect_errno=0 (as of PHP 5.5.9).

[#2] webmaster at aryes dot fr [2015-07-18 06:58:16]

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.

[#3] Ben [2015-03-03 11:28:12]

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();

[#4] linguafranca2003 at yahoo dot com [2014-11-28 17:21:35]

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
        
}
}
?>

[#5] andres at 21brains dot com [2014-06-03 09:39:02]

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.

[#6] fugyl13 at gmail dot com [2014-04-01 16:41:48]

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.

[#7] paul at mtnlist dot com [2013-06-02 08:19:16]

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.

[#8] oleg at mastak dot fi [2013-04-19 13:02:18]

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.

[#9] Anonymous [2009-09-13 17:37:12]

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_namenull'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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