boost 编码转换:
#include <boost/locale.hpp>
boost::locale::conv::from_utf<char>("utf-8字串", "GBK");
boost::locale::conv::to_utf<char>("GBK字串","GBK")
string source = "....";
string s = boost::locale::conv::between( source, "UTF-8", "BIG5" );
ref: http://blog.youkuaiyun.com/gong_xucheng/article/details/25957795
http://blog.youkuaiyun.com/leitianjun/article/details/24658655