/**
 * BBCode替换函数
 *
 * @param 
 * @arrange (512.笔记) jb51.cc
 **/
function BBcode($texto){
   $a = array(
      "/\[i\](.*?)\[\/i\]/is","/\[b\](.*?)\[\/b\]/is","/\[u\](.*?)\[\/u\]/is","/\[img\](.*?)\[\/img\]/is","/\[url=(.*?)\](.*?)\[\/url\]/is","/\[size=(.*?)\](.*?)\[\/size\]/is",);
   $b = array(
      "<i>$1</i>","<b>$1</b>","<u>$1</u>","<img src=\"$1\" />","<a href=\"$1\" target=\"_blank\">$2</a>",'<font size=$1>$2</font>',);
   $texto = preg_replace($a,$b,$texto);
   $texto = nl2br($texto);
   return $texto;
}
    if(isset($_GET['txt'])) {
        echo "Has introducido: ".bbcode($_GET['txt']);
    }

/***   代码来自编程之家 jb51.cc（jb51.cc）   ***/