PHP undefined variable mysqli connection

问题

I have a mysql connection which is included in a separate file:

require 'settings.php';

and I have a file with all functions, also included:

require 'functions.php';

In the settings there it looks like this:

$db = mysqli_connect("host", "username", "passwort", "database");
    if(!$db) {
        exit("Error: ".mysqli_connect_error());
    }

and a function uses this connection like this:

function includehomepage() {
            $data = array();
            $query = "SELECT pagecontent FROM `pages` WHERE `id` = `0`";
            $query = mysqli_query($db, $query);
            $data = mysqli_fetch_assoc($query);
            return $data['pagecontent'];
        }

But I get an error message like this:

Undefined variable: db in /var/... on line 18

Do you have an answer? The variable have to be defined in the included file.. I am confused. Thanks for your answers!

回答1:

Variable scope problem. Look at global

function includehomepage() {
   global $db;
   $data = array();
   $query = "SELECT pagecontent FROM `pages` WHERE `id` = '0'";
   $query = mysqli_query($db, $query);
   $data = mysqli_fetch_assoc($query);
   return $data['pagecontent'];
}

回答2:

$db is a global variable to includehomepage function. If you want to access it, then you have to pass it to the function or declare it as global inside the function.

like

function includehomepage() {
     global $db;   
     $data = array();
     $query = "SELECT pagecontent FROM `pages` WHERE `id` = '0'";
     $query = mysqli_query($db, $query);
     $data = mysqli_fetch_assoc($query);
     return $data['pagecontent'];
}

or have it as a parameter in your function and pass it via call.

function includehomepage($db) {
     $data = array();
     $query = "SELECT pagecontent FROM `pages` WHERE `id` = '0'";
     $query = mysqli_query($db, $query);
     $data = mysqli_fetch_assoc($query);
     return $data['pagecontent'];
}
includehomepage($db);

来源：https://stackoverflow.com/questions/25994328/php-undefined-variable-mysqli-connection