php 按引用传递的使用

测试1

function add($a)
{
$a+=1;
echo $a."<hr>";
}
$a = 1;
add($a);
echo $a

输出： 

1

1

测试2

function add($a)
{
$a+=1;
echo $a."<hr>";
}
$a = 1;
add(& $a);
echo $a

输出虽然达到了效果，但是会报错

Warning: Call-time pass-by-reference has been deprecated; If you would like to pass it by reference, modify the declaration of add(). If you would like to enable call-time pass-by-reference, you can set allow_call_time_pass_reference to true in your INI file in path on line 8

2

2

测试3

function add(& $a)
{
$a+=1;
echo $a."<hr>";
}
$a = 1;
add($a);
echo $a

结果

2

2

这个才是正确的