在不同环境中的PHP会话变量将无法正常工作

Question

The following script works under windows xampp, php 5.3.8

session_start();
    if (empty($_SESSION['myvar']) && empty($_GET['myvar'])) {
        $myvar = "some_value";
    } elseif (!empty($_GET['myvar'])) {
        $_SESSION['myvar'] = $_GET['myvar'];
    }
    $_SESSION['myvar'] = $myvar;

but on ubuntu server, php 5.3.10 if I var_dump($myvar) the value is null

Answer 1

Have you considered you may be defining your session variable twice, overwriting the first defined within your if statement? Also if you were to run the following code while !empty($_GET['myvar']) is true:

session_start();
if (empty($_SESSION['myvar']) && empty($_GET['myvar'])) {
    $myvar = "some_value";
} elseif (!empty($_GET['myvar'])) {
    $_SESSION['myvar'] = $_GET['myvar'];
}
$_SESSION['myvar'] = $myvar;

You would most likley get an undefined variable warning because your not setting $myvar. Try this:

session_start();
if (empty($_SESSION['myvar']) && empty($_GET['myvar'])) {
    $myvar = "some_value";
    $_SESSION['myvar'] = $myvar;
} elseif (!empty($_GET['myvar'])) {
    $_SESSION['myvar'] = $_GET['myvar'];
}

Answer 2

You only add value to $myvar if the session or the get parameter is empty. Otherwise it is null. How about this:

session_start();
$my_var = isset($_SESSION['my_var'] ? $_SESSION['my_var'] : 'default_value';
if(empty($_SESSION['myvar']) && empty($_GET['myvar'])){
    $myvar = 'some_value';
} elseif(!empty($_GET['my_var'))) {
    $myvar = $_GET['myvar'];
}
$_SESSION['my_var'] = $myvar;

Or simply:

session_start();
$_SESSION['my_var'] = isset($_GET['my_var']) ? $_GET['my_var'] : (isset($_SESSION['my_var']) ? $_SESSION['my_var'] : 'default_value');

Answer 3

empty($_SESSION['myvar']) && empty($_GET['myvar'])

It's false for all time. Becase on fist time $_SESSION['myvar'] is empty, and $_GET['myvar'] not empty：

$_SESSION['myvar'] = $myvar; // now $myvar is empty



 if (empty($_SESSION['myvar']) && empty($_GET['myvar'])) {
        $_SESSION['myvar'] = "some_value";
    } elseif (!empty($_GET['myvar'])) {
        $_SESSION['myvar'] = $_GET['myvar'];
    }