php unset（）它到底是做什么的？_course

<div class="post-text" itemprop="text"> <p>The PHP <a href="http://www.php.net/manual/en/function.unset.php" rel="nofollow">documentation</a> states the following about the <code>unset()</code> language construct:</p> <blockquote> <p>destroys the specified variables.</p> <p>Unset a given variable</p> </blockquote> <p>What does this really mean? Just destroy the variable content; empty out a variable and give it the value <code>null</code>? Or does it mean, wipe out the variable not just it's content but everything?</p> <p>I wrote the following:</p> <pre><code>$a = "tom"; unset($a); var_dump($a); </code></pre> <p>and got this:</p> <pre><code>Notice: Undefined variable: a in... </code></pre> </div>

php for循环里unset的问题_course

$arr=array('苹果','梨','香蕉','苹果','苹果','苹果'); for ($i=0; $i <= count($arr); $i++) { if ($arr[$i]=="苹果") { unset($arr[$i]); } } var_dump($arr); 举这么一个简单例子,我想把所有苹果的元素删除,但不知道为什么..这样写不行,也搜不出不个所以然,来请教下大家

php页面结尾都需要unset变量来释放内存吗_course

php页面结尾都需要unset变量来释放内存吗？还是执行完了自动就会释放内存，不需要主动unset？经常遇到out of memory错误，服务器内存还有很多，memory_limit也已经设很大51