How can you reliably determine in PHP whether a variable is set or has the value 0, FALSE, or NULL?

When checking if a variable is set or has the value 0, FALSE, or NULL in PHP, you can use the `isset()` function in combination with strict comparison operators (`===` and `!==`). This allows you to differentiate between a variable that is not set and one that is set to a specific value. 

$var = 0;

if (isset($var) && $var !== NULL && $var !== FALSE) {
    // Variable is set and its value is not 0, FALSE, or NULL
    echo "Variable is set and has a valid value.";
} else {
    // Variable is not set or its value is 0, FALSE, or NULL
    echo "Variable is not set or has a value of 0, FALSE, or NULL.";
}

Keywords

PHP variable isset comparison NULL

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