php 地址引用(&)

$a = 1;
$b = 2;
$c = &$a; //变量c地址指向变量a
$c = 2; //这个其实没什么用
if(($a = 3) > 0 || ($b = $a) > 0){ //条件判断中前者成立，后者不执行
//$a = 3, $b = 2, $c = 3
$a++; //$a = $c = 4(变量c地址指向了a)
$b++; //$b = 3
$c++; //$c = $a
}
printf("%d,%d,%x/n",$a,$b,$c); //结果5,3,5
//$a = 5, $b = 3, $c = 5
if(($c = 3) > 0 || ($b = $a) > 0 ){//条件判断中前者成立，后者不执行
$a++; //$a = $c + 1
$b++; //$b = 4
}
//$c = $a = 4
printf("%d,%d,%x/n",$a,$b,$c); //结果4,4,4

$a = 5;
$b = &$a;
unset($a);
var_dump($a);
echo $b;