php unset

php里面的unset 可以把值置空，但是并不会改变值已经有的索引位置

 1 $testArr=array('frist','second','third');
 2 echo '<pre>';
 3 echo '<br/>---------------------------------proto ------------------------------</br>';
 4 print_r($testArr);
 5 foreach($testArr as $key=>$val){
 6     unset($testArr[$key]);
 7 }
 8 echo '<br/>---------------------opo---------------------------</br>';
 9 print_r($testArr);
10 $testArr[]='good!';
11 echo '<br/>---------------------add---------------------------</br>';
12 print_r($testArr);
13 echo '</pre>';

If a static variable is unset() inside of a function, unset() destroys the variable only in the context of the rest of a function. Following calls will restore the previous value of a variable.

 1 function foo()
 2 {
 3     static $bar;
 4     $bar++;
 5     echo "Before unset: $bar, ";
 6     unset($bar);
 7     $bar = 23;
 8     echo "after unset: $bar<br/>";
 9 }
10 
11 foo();
12 foo();
13 foo();
14 


vld分析：
15 function foos(&$bar) 
16 {
17     unset($bar);
18     $bar = "blah";
19 }
20 
21 $bar = 'something';
22 echo "$bar<br/>";
23 
24 foos($bar);
25 echo "$bar<br/>";

If a variable that is PASSED BY REFERENCE is unset() inside of a function, only the local variable is destroyed. The variable in the calling environment will retain the same value as before unset() was called.

这是手册中发现的，突然感觉把手册再翻一遍，是个正确的选择