取消设置变量，而不检查变量是否已被使用或声明

Question

To unset a variable without cheking whether it has been already used or declared.Which is valid in PHP: (a) or (b)? Although both works. In the sample code below,forward referencing is used,how PHP handles it internally?

(a)

while(stmt1->fetch())
{
   unset($data);
   $i=0;
   while(stmt2->fetch())
   {
     //Some code.......
     $data[$i] = $some_Value;
     $i++;
   }
}

(b)

while(stmt1->fetch())
{
   if(isset($data))
   {
     unset($data);
   }
   $i=0;
   while(stmt2->fetch())
   {
     //Some code.......
     $data[$i] = $some_Value;
     $i++;
   }
}

Answer 1

Instead of unsetting the variable, set it with an initial value. This conveys the intention much clearer.

Also, you don't need to keep track of $i to insert a new element:

while ($stmt1->fetch()) {
    $data = []; //Initialize empty array. This is PHP 5.4+ syntax.
    while ($stmt2->fetch()) {
        $data[] = $someValue; //$array[] means "Push new element to this array"
    }
}