How can undefined constants be avoided in PHP code when accessing $_GET variables?

Undefined constants can be avoided in PHP code when accessing $_GET variables by first checking if the key exists in the $_GET array using the isset() function. This ensures that the code does not try to access a key that does not exist, which would result in an undefined constant error. If the key exists, then it can be safely accessed to retrieve the value. 

if(isset($_GET['key'])){
    $value = $_GET['key'];
    // Use $value safely
} else {
    // Handle case where key is not set
}

Keywords

PHP $_GET variables defined constants isset() error_reporting

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