boost::algorithm::to_lower_copy — 转换为小写。
// In header: <boost/algorithm/string/case_conv.hpp> template<typename OutputIteratorT, typename RangeT> OutputIteratorT to_lower_copy(OutputIteratorT Output, const RangeT & Input, const std::locale & Loc = std::locale()); template<typename SequenceT> SequenceT to_lower_copy(const SequenceT & Input, const std::locale & Loc = std::locale());