$txtContent = iconv("utf-8",'GBK',$txtContent);

utf-8直接转gbk，这样问题就来了，当有些字符无法转换的时候就从此处断开，导致内容不完整。后来又重新查手册，才发现iconv还有两个可选的辅助参数：TRANSLIT和IGNORE ，(其中IGNORE 就是说遇到无法转换的就跳过)。 其实也怪自己太粗心，刚开始一看iconv函数参数就三个，而且例子中也没有特别的，就懒得去看英文解释了，直接使用，直到出现了问题。

string iconv ( string in_charset, string out_charset, string str )

Performs a character set conversion on the string str from in_charset to out_charset. Returns the converted string or FALSE on failure.

If you append the string //TRANSLIT to out_charset transliteration is activated. This means that when a character can't be represented in the target charset, it can be approximated through one or several similarly looking characters. If you append the string //IGNORE, characters that cannot be represented in the target charset are silently discarded. Otherwise, str is cut from the first illegal character.