diff --git a/src/FullSegment.hpp b/src/FullSegment.hpp
index 65e482a..624383e 100644
--- a/src/FullSegment.hpp
+++ b/src/FullSegment.hpp
@@ -47,12 +47,6 @@ class FullSegment: public SegmentBase {
 
   using SegmentBase::cut;
   bool cut(Unicode::const_iterator begin, Unicode::const_iterator end, vector<Unicode>& res) const {
-    assert(dictTrie_);
-    if (begin >= end) {
-      LogError("begin >= end");
-      return false;
-    }
-
     //resut of searching in trie tree
     DagType tRes;
 
@@ -64,6 +58,7 @@ class FullSegment: public SegmentBase {
 
     //tmp variables
     int wordLen = 0;
+    assert(dictTrie_);
     for (Unicode::const_iterator uItr = begin; uItr != end; uItr++) {
       //find word start from uItr
       if (dictTrie_->find(uItr, end, tRes, 0)) {
@@ -93,12 +88,6 @@ class FullSegment: public SegmentBase {
   }
 
   bool cut(Unicode::const_iterator begin, Unicode::const_iterator end, vector<string>& res) const {
-    assert(dictTrie_);
-    if (begin >= end) {
-      LogError("begin >= end");
-      return false;
-    }
-
     vector<Unicode> uRes;
     if (!cut(begin, end, uRes)) {
       LogError("get unicode cut result error.");
@@ -107,11 +96,8 @@ class FullSegment: public SegmentBase {
 
     string tmp;
     for (vector<Unicode>::const_iterator uItr = uRes.begin(); uItr != uRes.end(); uItr++) {
-      if (TransCode::encode(*uItr, tmp)) {
-        res.push_back(tmp);
-      } else {
-        LogError("encode failed.");
-      }
+      TransCode::encode(*uItr, tmp);
+      res.push_back(tmp);
     }
 
     return true;
diff --git a/src/HMMSegment.hpp b/src/HMMSegment.hpp
index f384eb2..5cf0bf6 100644
--- a/src/HMMSegment.hpp
+++ b/src/HMMSegment.hpp
@@ -90,9 +90,7 @@ class HMMSegment: public SegmentBase {
     size_t offset = res.size();
     res.resize(res.size() + words.size());
     for(size_t i = 0; i < words.size(); i++) {
-      if(!TransCode::encode(words[i], res[offset + i])) {
-        LogError("encode failed.");
-      }
+      TransCode::encode(words[i], res[offset + i]);
     }
     return true;
   }
diff --git a/src/Limonp/StringUtil.hpp b/src/Limonp/StringUtil.hpp
index 61ebd60..0efab05 100644
--- a/src/Limonp/StringUtil.hpp
+++ b/src/Limonp/StringUtil.hpp
@@ -197,10 +197,7 @@ bool utf8ToUnicode(const string& str, Uint16Container& vec) {
 }
 
 template <class Uint16ContainerConIter>
-bool unicodeToUtf8(Uint16ContainerConIter begin, Uint16ContainerConIter end, string& res) {
-  if(begin >= end) {
-    return false;
-  }
+void unicodeToUtf8(Uint16ContainerConIter begin, Uint16ContainerConIter end, string& res) {
   res.clear();
   uint16_t ui;
   while(begin != end) {
@@ -217,7 +214,6 @@ bool unicodeToUtf8(Uint16ContainerConIter begin, Uint16ContainerConIter end, str
     }
     begin ++;
   }
-  return true;
 }
 
 
@@ -225,7 +221,7 @@ template <class Uint16Container>
 bool gbkTrans(const char* const str, size_t len, Uint16Container& vec) {
   vec.clear();
   if(!str) {
-    return false;
+    return true;
   }
   size_t i = 0;
   while(i < len) {
@@ -251,10 +247,7 @@ bool gbkTrans(const string& str, Uint16Container& vec) {
 }
 
 template <class Uint16ContainerConIter>
-bool gbkTrans(Uint16ContainerConIter begin, Uint16ContainerConIter end, string& res) {
-  if(begin >= end) {
-    return false;
-  }
+void gbkTrans(Uint16ContainerConIter begin, Uint16ContainerConIter end, string& res) {
   res.clear();
   //pair<char, char> pa;
   char first, second;
@@ -270,7 +263,6 @@ bool gbkTrans(Uint16ContainerConIter begin, Uint16ContainerConIter end, string&
     }
     begin++;
   }
-  return true;
 }
 
 /*
diff --git a/src/MPSegment.hpp b/src/MPSegment.hpp
index 05f8954..a0d3a57 100644
--- a/src/MPSegment.hpp
+++ b/src/MPSegment.hpp
@@ -42,10 +42,7 @@ class MPSegment: public SegmentBase {
     size_t offset = res.size();
     res.resize(res.size() + words.size());
     for(size_t i = 0; i < words.size(); i++) {
-      if(!TransCode::encode(words[i], res[i + offset])) {
-        LogError("encode failed.");
-        res[i + offset].clear();
-      }
+      TransCode::encode(words[i], res[i + offset]);
     }
     return true;
   }
diff --git a/src/MixSegment.hpp b/src/MixSegment.hpp
index 18b0b84..aace901 100644
--- a/src/MixSegment.hpp
+++ b/src/MixSegment.hpp
@@ -83,9 +83,7 @@ class MixSegment: public SegmentBase {
     size_t offset = res.size();
     res.resize(res.size() + uRes.size());
     for(size_t i = 0; i < uRes.size(); i ++, offset++) {
-      if(!TransCode::encode(uRes[i], res[offset])) {
-        LogError("encode failed.");
-      }
+      TransCode::encode(uRes[i], res[offset]);
     }
     return true;
   }
diff --git a/src/QuerySegment.hpp b/src/QuerySegment.hpp
index 4655d30..1e8ba13 100644
--- a/src/QuerySegment.hpp
+++ b/src/QuerySegment.hpp
@@ -29,11 +29,6 @@ class QuerySegment: public SegmentBase {
   }
   using SegmentBase::cut;
   bool cut(Unicode::const_iterator begin, Unicode::const_iterator end, vector<Unicode>& res) const {
-    if (begin >= end) {
-      LogError("begin >= end");
-      return false;
-    }
-
     //use mix cut first
     vector<Unicode> mixRes;
     if (!mixSeg_.cut(begin, end, mixRes)) {
@@ -64,11 +59,6 @@ class QuerySegment: public SegmentBase {
 
 
   bool cut(Unicode::const_iterator begin, Unicode::const_iterator end, vector<string>& res) const {
-    if (begin >= end) {
-      LogError("begin >= end");
-      return false;
-    }
-
     vector<Unicode> uRes;
     if (!cut(begin, end, uRes)) {
       LogError("get unicode cut result error.");
@@ -77,11 +67,8 @@ class QuerySegment: public SegmentBase {
 
     string tmp;
     for (vector<Unicode>::const_iterator uItr = uRes.begin(); uItr != uRes.end(); uItr++) {
-      if (TransCode::encode(*uItr, tmp)) {
-        res.push_back(tmp);
-      } else {
-        LogError("encode failed.");
-      }
+      TransCode::encode(*uItr, tmp);
+      res.push_back(tmp);
     }
 
     return true;
diff --git a/src/TransCode.hpp b/src/TransCode.hpp
index d46bfbb..ba1bfdd 100644
--- a/src/TransCode.hpp
+++ b/src/TransCode.hpp
@@ -23,16 +23,16 @@ inline bool decode(const string& str, Unicode& res) {
 #endif
 }
 
-inline bool encode(Unicode::const_iterator begin, Unicode::const_iterator end, string& res) {
+inline void encode(Unicode::const_iterator begin, Unicode::const_iterator end, string& res) {
 #ifdef CPPJIEBA_GBK
-  return gbkTrans(begin, end, res);
+  gbkTrans(begin, end, res);
 #else
-  return unicodeToUtf8(begin, end, res);
+  unicodeToUtf8(begin, end, res);
 #endif
 }
 
-inline bool encode(const Unicode& uni, string& res) {
-  return encode(uni.begin(), uni.end(), res);
+inline void encode(const Unicode& uni, string& res) {
+  encode(uni.begin(), uni.end(), res);
 }
 
 // compiler is expected to optimized this function to avoid return value copy