diff --git a/demo/keywordext_demo.cpp b/demo/keywordext_demo.cpp
index c305c67..648c1e2 100644
--- a/demo/keywordext_demo.cpp
+++ b/demo/keywordext_demo.cpp
@@ -21,7 +21,7 @@ void testKeyWordExt(const char * dictPath, const char * filePath)
 		return ;
 	}
 	ifstream ifile(filePath);
-	vector<string> res;
+	vector<KeyWordInfo> res;
 	string line;
 	while(getline(ifile, line))
 	{
@@ -29,7 +29,7 @@ void testKeyWordExt(const char * dictPath, const char * filePath)
 		if(!line.empty())
 		{
 			ext.extract(line, res, 20);
-			cout<<line<<"\n"<<joinStr(res,",")<<endl;
+			cout<<line<<'\n'<<joinWordInfos(res)<<endl;
 		}
 
 	}
@@ -57,15 +57,15 @@ void testKeyWordExt2(const char * dictPath, const char * filePath)
 
 	ifstream ifile(filePath);
 	vector<string> words;
-	vector<string> keywords;
+	vector<KeyWordInfo> res;
 	string line;
 	while(getline(ifile, line))
 	{
 		if(!line.empty())
 		{
 			seg.cutDAG(line, words);
-			ext.extract(words, keywords, 20);
-			cout<<line<<"\n"<<joinStr(keywords," ")<<endl;
+			ext.extract(words, res, 20);
+			cout<<line<<"\n"<<joinWordInfos(res)<<endl;
 		}
 
 	}
@@ -73,13 +73,26 @@ void testKeyWordExt2(const char * dictPath, const char * filePath)
 	ext.dispose();
 }
 
+const char * const DEFAULT_DICTPATH = "../dicts/jieba.dict.gbk";
+
 int main(int argc, char ** argv)
 {
-	if(argc != 3)
+	ArgvContext arg(argc, argv);
+	string dictPath = arg["--dictpath"];
+	if("" == dictPath)
 	{
-		cerr<<"usage: "<<argv[0]<<" ../dicts/jieba.dict.gbk filename"<<endl;
+		dictPath = DEFAULT_DICTPATH;
+	}
+	if("" == arg[1])
+	{
+		cout<<"usage: \n\t"<<argv[0]<<" [options] <filename>\n"
+		    <<"options:\n"
+		    <<"\t--dictpath\tIf is not specified, the default is "<<DEFAULT_DICTPATH<<"\n"
+		    <<"\t--encoding\tSupported encoding methods are [gbk, utf-8] for now. \n\t\t\tIf is not specified, the default is gbk."
+			<<endl;
 		return -1;
 	}
-	testKeyWordExt(argv[1], argv[2]);
+	
+	testKeyWordExt(dictPath.c_str(), arg[1].c_str());
 	return 0;
 }
diff --git a/src/KeyWordExt.cpp b/src/KeyWordExt.cpp
index d4de73c..2bc98d9 100644
--- a/src/KeyWordExt.cpp
+++ b/src/KeyWordExt.cpp
@@ -92,184 +92,144 @@ namespace CppJieba
 		for(uint i = 0; i < wordInfos.size(); i++)
 		{
 			KeyWordInfo& wInfo = wordInfos[i];
-			double logWordFreq = 1.0;//_segment.getWordWeight(wInfo.word);
-			wInfo.idf = -logWordFreq;
-			size_t wLen = TransCode::getWordLength(wInfo.word);
-			if(0 == wLen)
+			wInfo.idf = - wInfo.logFreq;
+			if(0 == wInfo.wLen)
 			{
-				LogFatal("getUtf8WordLen(%s) return 0");
+				LogFatal("wLen is 0!");
+				return false;
 			}
-			wInfo.weight = log(double(wLen + 1)) * wInfo.idf;
+			wInfo.weight = log(double(wInfo.wLen + 1)) * wInfo.idf;
 		}
 		sort(wordInfos.begin(), wordInfos.end(), _wordInfoCompare);
 		return true;
 	}
 
-	bool KeyWordExt::_extractTopN(const vector<string>& words, vector<string>& keywords, uint topN)
+	bool KeyWordExt::_extTopN(vector<KeyWordInfo>& wordInfos, uint topN)
 	{
-		keywords.clear();
-		vector<KeyWordInfo> wordInfos;
-		for(uint i = 0; i < words.size(); i++)
+		int dis = wordInfos.size() - topN;
+		if(dis <= 0)
 		{
-			KeyWordInfo wInfo;
-			wInfo.word = words[i];
-			wordInfos.push_back(wInfo);
+			return true;
 		}
 		
-		_sortWLIDF(wordInfos);
-#ifdef DEBUG
-		LogDebug(string_format("calc weight & sorted:%s",joinWordInfos(wordInfos).c_str()));
-#endif
-		
-		_prioritizeSubWords(wordInfos);
-#ifdef DEBUG
-		LogDebug(string_format("_prioritizeSubWords res:%s", joinWordInfos(wordInfos).c_str()));
-#endif
-		//extract TopN
-		for(uint i = 0; i < topN && i < wordInfos.size(); i++)
+		if(uint(dis) <= topN)
 		{
-			keywords.push_back(wordInfos[i].word);
+			for(int i = 0; i< dis; i++)
+			{
+				wordInfos.pop_back();
+			}
+		}
+		else// in case that topN << size;
+		{
+			
+			vector<KeyWordInfo> tmp(wordInfos.begin(), wordInfos.begin() + topN);
+			wordInfos.swap(tmp);
 		}
 		return true;
 	}
 
 
-	bool KeyWordExt::extract(const vector<string>& _words, vector<string>& keywords, uint topN)
+	bool KeyWordExt::extract(const vector<string>& words, vector<KeyWordInfo>& keyWordInfos, uint topN)
 	{
-		if(_words.empty())
+		if(words.empty())
 		{
 			return false;
 		}
 
-		vector<string> words(_words);
-
-#ifdef DEBUG
+#ifdef DEBU
 		LogDebug(string_format("words:[%s]", joinStr(words, ",").c_str()));
 #endif
 
-		bool retFlag = _filter(words);
-		if(!retFlag)
+		keyWordInfos.clear();
+		for(uint i = 0; i < words.size(); i++)
 		{
-			LogError("_filter failed.");
-			return false;
+			keyWordInfos.push_back(words[i]);
 		}
 
-#ifdef DEBUG
-		LogDebug(string_format("_filter res:[%s]", joinStr(words, ",").c_str()));
-#endif
-
-		retFlag = _extractTopN(words, keywords, topN);
-		if(!retFlag)
-		{
-			LogError("_extractTopN failed.");
-			return false;
-		}
-		//LogDebug("_extractTopN finished.");
-
-#ifdef DEBUG
-		LogDebug(string_format("ext res:[%s]", joinStr(keywords, ",").c_str()));
-#endif
-		
-		return true;
+		return _extract(keyWordInfos, topN);
 	}
 
-	bool KeyWordExt::extract(const string& title, vector<string>& keywords, uint topN)
+	bool KeyWordExt::extract(const string& title, vector<KeyWordInfo>& keyWordInfos, uint topN)
 	{
 		if(title.empty())
 		{
 			return false;
 		}
+		
+		vector<TrieNodeInfo> trieNodeInfos; 
+		_segment.cutDAG(title, trieNodeInfos);
 
-#ifdef DEBUG
-		LogDebug(string_format("title:[%s]",title.c_str()));
-#endif
-
-		bool retFlag;
-		vector<string> words;
-		retFlag = _segment.cutDAG(title, words);
-		if(!retFlag)
+		keyWordInfos.clear();
+		for(uint i = 0; i < trieNodeInfos.size(); i++)
 		{
-			LogError(string_format("cutDAG(%s) failed.", title.c_str()));
-			return false;
+			keyWordInfos.push_back(trieNodeInfos[i]);
 		}
-#ifdef DEBUG
-		LogDebug(string_format("cutDAG result:[%s]", joinStr(words, ",").c_str()));
-#endif
+		return _extract(keyWordInfos, topN);
+	}
 
-		retFlag = _filter(words);
-		if(!retFlag)
+	bool KeyWordExt::_extract(vector<KeyWordInfo>& keyWordInfos, uint topN)
+	{
+		if(!_filter(keyWordInfos))
 		{
 			LogError("_filter failed.");
 			return false;
 		}
 
-#ifdef DEBUG
-		LogDebug(string_format("_filter res:[%s]", joinStr(words, ",").c_str()));
-#endif
-
-		retFlag = _extractTopN(words, keywords, topN);
-		if(!retFlag)
+		if(!_sortWLIDF(keyWordInfos))
 		{
-			LogError("_extractTopN failed.");
+			LogError("_sortWLIDF failed.");
+			return false;
+		}
+
+		if(!_extTopN(keyWordInfos, topN))
+		{
+			LogError("_extTopN failed.");
 			return false;
 		}
-		//LogDebug("_extractTopN finished.");
 
-#ifdef DEBUG
-		LogDebug(string_format("ext res:[%s]", joinStr(keywords, ",").c_str()));
-#endif
 		return true;
 	}
 
-	bool KeyWordExt::_filter(vector<string>& strs)
+	bool KeyWordExt::_filter(vector<KeyWordInfo>& wordInfos)
 	{
-		bool retFlag;
-		retFlag = _filterDuplicate(strs);
-		if(!retFlag)
+		if(!_filterDuplicate(wordInfos))
 		{
 			LogError("_filterDuplicate failed.");
 			return false;
 		}
-		//LogDebug(string_format("_filterDuplicate res:[%s]", joinStr(strs, ",").c_str()));
 
-		retFlag = _filterSingleWord(strs);
-		if(!retFlag)
+		if(!_filterSingleWord(wordInfos))
 		{
 			LogError("_filterSingleWord failed.");
 			return false;
 		}
-		//LogDebug(string_format("_filterSingleWord res:[%s]", joinStr(strs, ",").c_str()));
 
-		retFlag = _filterStopWords(strs);
-		if(!retFlag)
+		if(!_filterStopWords(wordInfos))
 		{
 			LogError("_filterStopWords failed.");
 			return false;
 		}
-		//LogDebug(string_format("_filterStopWords res:[%s]", joinStr(strs, ",").c_str()));
 
-		retFlag = _filterSubstr(strs);
-		if(!retFlag)
+		if(!_filterSubstr(wordInfos))
 		{
 			LogError("_filterSubstr failed.");
 			return false;
 		}
-		//LogDebug(string_format("_filterSubstr res:[%s]", joinStr(strs, ",").c_str()));
 
 		return true;
 	}
 
-	bool KeyWordExt::_filterStopWords(vector<string>& strs)
+	bool KeyWordExt::_filterStopWords(vector<KeyWordInfo>& wordInfos)
 	{
 		if(_stopWords.empty())
 		{
 			return true;
 		}
-		for(VSI it = strs.begin(); it != strs.end();)
+		for(vector<KeyWordInfo>::iterator it = wordInfos.begin(); it != wordInfos.end();)
 		{
-			if(_stopWords.find(*it) != _stopWords.end())
+			if(_stopWords.find(it->word) != _stopWords.end())
 			{
-				it = strs.erase(it);
+				it = wordInfos.erase(it);
 			}
 			else
 			{
@@ -280,33 +240,33 @@ namespace CppJieba
 	}
 
 
-	bool KeyWordExt::_filterDuplicate(vector<string>& strs)
+	bool KeyWordExt::_filterDuplicate(vector<KeyWordInfo>& wordInfos)
 	{
 		set<string> st;
-		for(VSI it = strs.begin(); it != strs.end(); )
+		for(vector<KeyWordInfo>::iterator it = wordInfos.begin(); it != wordInfos.end(); )
 		{
-			if(st.find(*it) != st.end())
+			if(st.find(it->word) != st.end())
 			{
-				it = strs.erase(it);
+				it = wordInfos.erase(it);
 			}
 			else
 			{
-				st.insert(*it);
+				st.insert(it->word);
 				it++;
 			}
 		}
 		return true;
 	}
 
-	bool KeyWordExt::_filterSingleWord(vector<string>& strs)
+	bool KeyWordExt::_filterSingleWord(vector<KeyWordInfo>& wordInfos)
 	{
-		for(vector<string>::iterator it = strs.begin(); it != strs.end();)
+		for(vector<KeyWordInfo>::iterator it = wordInfos.begin(); it != wordInfos.end();)
 		{
 
 			// filter single word
-			if(1 == TransCode::getWordLength(*it)) 
+			if(1 == it->wLen)
 			{
-				it = strs.erase(it);
+				it = wordInfos.erase(it);
 			}
 			else
 			{
@@ -316,27 +276,31 @@ namespace CppJieba
 		return true;
 	}
 
-	bool KeyWordExt::_filterSubstr(vector<string>& strs)
+	bool KeyWordExt::_filterSubstr(vector<KeyWordInfo>& wordInfos)
 	{
-		vector<string> tmp = strs;
+		vector<string> tmp ;
+		for(uint i = 0; i < wordInfos.size(); i++)
+		{
+			tmp.push_back(wordInfos[i].word);
+		}
 		set<string> subs;
-		for(VSI it = strs.begin(); it != strs.end(); it ++)
+		for(vector<KeyWordInfo>::iterator it = wordInfos.begin(); it != wordInfos.end(); it ++)
 		{
 			for(uint j = 0; j < tmp.size(); j++)
 			{
-				if(*it != tmp[j] && string::npos != tmp[j].find(*it, 0))
+				if(it->word != tmp[j] && string::npos != tmp[j].find(it->word, 0))
 				{
-					subs.insert(*it);
+					subs.insert(it->word);
 				}
 			}
 		}
 
 		//erase subs from strs
-		for(VSI it = strs.begin(); it != strs.end(); )
+		for(vector<KeyWordInfo>::iterator it = wordInfos.begin(); it != wordInfos.end(); )
 		{
-			if(subs.end() != subs.find(*it))
+			if(subs.end() != subs.find(it->word))
 			{
-				it =  strs.erase(it);
+				it =  wordInfos.erase(it);
 			}
 			else
 			{
diff --git a/src/KeyWordExt.h b/src/KeyWordExt.h
index 3e8854f..eabf276 100644
--- a/src/KeyWordExt.h
+++ b/src/KeyWordExt.h
@@ -33,21 +33,22 @@ namespace CppJieba
 			bool dispose();
 
 		public:
-			bool extract(const string& title, vector<string>& keywords, uint topN);
-			bool extract(const vector<string>& words, vector<string>& keywords, uint topN);
+			bool extract(const string& title, vector<KeyWordInfo>& keyWordInfos, uint topN);
+			bool extract(const vector<string>& words, vector<KeyWordInfo>& keyWordInfos, uint topN);
 		private:
 			static bool _wordInfoCompare(const KeyWordInfo& a, const KeyWordInfo& b);
 		private:
-			bool _extractTopN(const vector<string>& words, vector<string>& keywords, uint topN);
+			bool _extract(vector<KeyWordInfo>& keyWordInfos, uint topN);
+			bool _extTopN(vector<KeyWordInfo>& wordInfos, uint topN);
 		private:
 			//sort by word len - idf
 			bool _sortWLIDF(vector<KeyWordInfo>& wordInfos);
 		private:
-			bool _filter(vector<string>& strs);
-			bool _filterDuplicate(vector<string>& strs);
-			bool _filterSingleWord(vector<string>& strs);
-			bool _filterSubstr(vector<string>& strs);
-			bool _filterStopWords(vector<string>& strs);
+			bool _filter(vector<KeyWordInfo>& );
+			bool _filterDuplicate(vector<KeyWordInfo>& );
+			bool _filterSingleWord(vector<KeyWordInfo>& );
+			bool _filterSubstr(vector<KeyWordInfo>& );
+			bool _filterStopWords(vector<KeyWordInfo>& );
 		private:
 			bool _prioritizeSubWords(vector<KeyWordInfo>& wordInfos);
 			bool _isContainSubWords(const string& word);
diff --git a/src/structs.h b/src/structs.h
index 9eed706..983c75e 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -1,7 +1,9 @@
 #ifndef CPPJIEBA_STRUCTS_H
 #define CPPJIEBA_STRUCTS_H
 
+#include <limits>
 #include "globals.h"
+#include "Trie.h"
 
 namespace CppJieba
 {
@@ -19,6 +21,13 @@ namespace CppJieba
 			freq = 0;
 			logFreq = 0.0;
 		}
+		TrieNodeInfo(const string& _word)
+		{
+			word = _word;
+			wLen = TransCode::getWordLength(_word);
+			freq = 0;
+			logFreq = -numeric_limits<double>::max();
+		}
 	};
 	
 	
@@ -36,7 +45,6 @@ namespace CppJieba
 		
 	};
 	*/
-	
 
 	struct KeyWordInfo: public TrieNodeInfo
 	{
@@ -47,10 +55,34 @@ namespace CppJieba
 			idf = 0.0;
 			weight = 0.0;
 		}
+		KeyWordInfo(const string& _word):TrieNodeInfo(_word)
+		{ 
+			idf = 0.0;
+			weight = 0.0;
+		}
+		KeyWordInfo(const TrieNodeInfo& trieNodeInfo)
+		{
+			word = trieNodeInfo.word;
+			freq = trieNodeInfo.freq;
+			wLen = trieNodeInfo.wLen;
+			tag = trieNodeInfo.tag;
+			logFreq = trieNodeInfo.logFreq;
+			idf = 0.0;
+			weight = 0.0;
+		}
 		string toString() const
 		{
 			return string_format("{word:%s,wLen:%d weight:%lf, idf:%lf}", word.c_str(), wLen, weight, idf);
 		}
+		KeyWordInfo& operator = (const TrieNodeInfo& trieNodeInfo)
+		{
+			word = trieNodeInfo.word;
+			freq = trieNodeInfo.freq;
+			wLen = trieNodeInfo.wLen;
+			tag = trieNodeInfo.tag;
+			logFreq = trieNodeInfo.logFreq;
+			return *this;
+		}
 	};
 
 	inline string joinWordInfos(const vector<KeyWordInfo>& vec)