创建全局变量时的困惑[重复]

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Reference: What is variable scope, which variables are accessible from where and what are “undefined variable” errors? 3 answers

How is $x and $y global variables if they don't have global written before them?

<!DOCTYPE html>
<html>
<body>

<?php 
$x = 75;
$y = 25; 

function addition() {
     $GLOBALS['z'] = $GLOBALS['x'] + $GLOBALS['y'];
}

addition();
echo $z;
?>

</body>
</html>

</div>

Because they are defined in the global namespace. A variable declared in a function can only be used within that function. You can overrule this by using the global operator that looks for the variable in the global name space.

function addition() {
     global $x, $y;
     $GLOBALS['z'] = $x + $y;
}

However the $GLOBALS variable is a place where all globals are stored. Since you define it in that function the $z variable is set.