mb_convert_encoding( $str, $encoding1,$encoding2 )；
$str，要转换编码的字符串
$encoding1，目标编码，如utf-8,gbk，大小写均可
$encoding2，原编码，如utf-8,gbk，大小写均可
实例1
<?php
$str='编码';
echo mb_convert_encoding($str, "UTF-8"); //编码转换为utf-8
?>
实例2
<?php
$str='编码';
echo mb_convert_encoding($str, "UTF-8", "GBK"); //已知原编码为GBK，转换为utf-8
?>
实例3
<?php
$str='编码';
echo mb_convert_encoding($str, "UTF-8", "auto"); //未知原编码，通过auto自动检测后，转换编码为utf-8
?>
