php = &

$a = 12;
$b =& $a;
echo $b; // 12
echo "\n";
$b = 23;
echo $a; // 23
echo "\n";
$a = 34;
echo $b; // 34
echo "\n";
$c = test($b);
echo $b; // 134
echo "\n";
echo $a; // 134
echo "\n";
echo $c; // 134
echo "\n";
$a = 342;
echo $c; // 134
echo "\n";
echo $b; // 342
echo "\n";
@$b =& test2($b);
echo $b; // 442
echo "\n";
$c =& $b;
$a = 154;
echo $c; // 154
echo "\n";
test3($c);
echo $c; // 0     $c 和 $and 绑定一起指向同一个内容，方法内又将 $and 和 $_GET[‘a‘] 绑定，但是test3方法内没有变量 $c ，函数内的操作不在$c影响范围
echo "\n";
$a = 111;

function test(&$and)
{
    return $and = $and + 100;
}
function test2($and)
{
    return $and = $and + 100;
}
function test3(&$and)
{
    return $and &= $_GET[‘a‘]; // $_GET[‘a‘] = 1
}
test(1); // 1是常量  不是变量