global定义变量用法

<?php
$a = 1;
$b = 2;

function Sum()
{
    global $a, $b;

    echo $a+$b;
}

Sum(); //输出3
?>

<?php
$a = 1;
$b = 2;

function Sum()
{
    global $a, $b;

    echo $a+$b;
}
$a = 20;
Sum(); //输出22
?>

<?php
$a = 1;
$b = 2;

echo '使用global之前'.$a.'</br>';
function Sum()
{
    global $a, $b;

    echo $a+$b;
}
Sum(); //使用global之前1      3
?>