Use Require_once() to include database connection variables correctly

问题

I'm a php newbie (but long time developer in other languages) and I'm trying some example db connections in "PHP, MySQL, & JavaScript". It shows an example file to include db connection variables (servername, username, password, database, etc.). I have a php file which has a handful of functions I wrote and one of them has a few SQL queries. For whatever reason, calling require_once in that file doesn't output any errors (I have E_ALL config'd) yet those variables in my database php file are null.

I called an echo with all the variables within that function to see what the heck is going on and of course it prints a blank line. What in the world is out of scope? I have to be missing something simple.

Here's an example of what I'm doing

db_login.php

<?php
    $db_server = 'localhost';
    // ....
?>

functions.php

<?php
    require_once('db_login.php');

    function myfunction() {
        echo "$db_server";
        // ...
    }
?>

Call me crazy, but shouldn't this be simple enough to work?

回答1:

The variables you declare in db_login.php are globals. In order to access them in your function, you need to use the $GLOBALS variable, e.g. $GLOBALS['db_server'], or declare them as global inside your function using the global keyword, e.g. global $db_server.

回答2:

PHP doesn't have function scope like Javascript, so you do not have access to the variables in db_login.php inside the functions of functions.php.

There are multiple ways of dealing with this. Due to your probable use of the server name global constants would probably be a good solution, since nothing can change them.

In your case you can do:

<?php
    require_once('db_login.php');
      // You have access to $db_server here.
      // Create a constant.
    define("DB_SERVER", $db_server);

    function myfunction() {
          // Using a constant. Note that there is no "$".
        echo DB_SERVER ;
          // Constants are interpreted inside double quotes too
        echo "\nMy constant is DB_SERVER";
        // ...
    }
?>

In your case having the server name as a constant is probably appropriate. If you are dealing with something that you want to treat as a true variable, you can pass the variable into the function by value or by reference:

myfunction($variable);

  // by value
function myfunction($pass_variable_to_me_by_value)
{
    echo $pass_variable_to_me_by_value;
    // ...
}

function myfunction(& $pass_variable_to_me_by_reference)
{
    echo $pass_variable_to_me_by_reference;
    // ...
}

As a note, in your case, using the global keyword or the $GLOBALS array inside a function is essentially the same as passing by reference., but if you are not passing from the global scope they can be very different (in a Class or from another function for example).

回答3:

Inside of the function "myfunction" you don't have access to these variable...

See more in: http://php.net/manual/en/language.variables.scope.php

来源：https://stackoverflow.com/questions/3615015/use-require-once-to-include-database-connection-variables-correctly

标签

php

scope

require-once