如何检查PHP是否已连接到数据库？

Question

Basically in pseudo code I'm looking for something like

if (connected_to_any_database()) {
    // do nothing
}
else {
    mysql_connect(...)
}

How do I implement

connected_to_any_database()

Answer 1

Have you tried mysql_ping()?

Checks whether or not the connection to the server is working. If it has gone down, an automatic reconnection is attempted.

Alternatively, a second (less reliable) approach would be:

$link = mysql_connect('localhost','username','password');
//(...)
if($link == false){
    //try to reconnect
}

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Update: From PHP 5.5 onwards, use mysqli_ping() instead.