1 求长度，最基本的
  $text = "sunny day";
$count = strlen($text); // $count = 9


2 字符串截取
  截取前多少个字符
  $article = "BREAKING NEWS: In ultimate irony, man bites dog."; $summary = substr_replace($article, "...", 40);

3 算单词数
  $article = "BREAKING NEWS: In ultimate irony, man bites dog."; $wordCount = str_word_count($article);
// $wordCount = 8

4 将字符串变成HTML的连接
$url = "W.J. Gilmore, LLC (http://www.wjgilmore.com)";
$url = preg_replace("/http://([A-z0-9./-]+)/", "$0", $url);

5 去除字符中的HTML字符串
  $text = strip_tags($input, "
");

6 nl2br:
  $comment = nl2br($comment);
  变成带HTML格式

7 Wordwrap
限制每行字数
$speech = "Four score and seven years ago our fathers brought forth, upon this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.";
echo wordwrap($speech, 30);

输出：
Four score and seven years ago our fathers brought forth, upon this continent, a new nation, conceived in Liberty, and dedicated to the proposition that all men are created equal.