diff --git a/src/BinaryDict.cpp b/src/BinaryDict.cpp
index 6357b2547..9302932d7 100644
--- a/src/BinaryDict.cpp
+++ b/src/BinaryDict.cpp
@@ -168,28 +168,30 @@ void BinaryDict::ConstructBuffer(std::string& keyBuf,
   // Write keys and values to buffers
   keyBuf.resize(keyTotalLength, '\0');
   valueBuf.resize(valueTotalLength, '\0');
-  char* pKeyBuffer = const_cast<char*>(keyBuf.c_str());
-  char* pValueBuffer = const_cast<char*>(valueBuf.c_str());
+  char* pKeyBuffer = keyBuf.data();
+  char* pValueBuffer = valueBuf.data();
   for (const std::unique_ptr<DictEntry>& entry : *lexicon) {
-    strcpy(pKeyBuffer, entry->Key().c_str());
-    keyOffset.push_back(pKeyBuffer - keyBuf.c_str());
-    pKeyBuffer += entry->KeyLength() + 1;
+    const std::string& key = entry->Key();
+    strcpy(pKeyBuffer, key.c_str());
+    keyOffset.push_back(pKeyBuffer - keyBuf.data());
+    pKeyBuffer += key.length() + 1;
     if (entry->NumValues() == 1) {
       const auto* svEntry =
           static_cast<const SingleValueDictEntry*>(entry.get());
-      strcpy(pValueBuffer, svEntry->Value().c_str());
-      valueOffset.push_back(pValueBuffer - valueBuf.c_str());
-      pValueBuffer += svEntry->Value().length() + 1;
+      const std::string& val = svEntry->Value();
+      strcpy(pValueBuffer, val.c_str());
+      valueOffset.push_back(pValueBuffer - valueBuf.data());
+      pValueBuffer += val.length() + 1;
     } else {
       const auto* mvEntry =
           static_cast<const MultiValueDictEntry*>(entry.get());
       for (const auto& value : mvEntry->Values()) {
         strcpy(pValueBuffer, value.c_str());
-        valueOffset.push_back(pValueBuffer - valueBuf.c_str());
+        valueOffset.push_back(pValueBuffer - valueBuf.data());
         pValueBuffer += value.length() + 1;
       }
     }
   }
-  assert(keyBuf.c_str() + keyTotalLength == pKeyBuffer);
-  assert(valueBuf.c_str() + valueTotalLength == pValueBuffer);
+  assert(keyBuf.data() + keyTotalLength == pKeyBuffer);
+  assert(valueBuf.data() + valueTotalLength == pValueBuffer);
 }
diff --git a/src/SerializedValues.cpp b/src/SerializedValues.cpp
index 1a96100b0..3aceba414 100644
--- a/src/SerializedValues.cpp
+++ b/src/SerializedValues.cpp
@@ -123,7 +123,7 @@ void SerializedValues::ConstructBuffer(std::string* valueBuffer,
   }
   // Write values to the buffer.
   valueBuffer->resize(*valueTotalLength, '\0');
-  char* pValueBuffer = const_cast<char*>(valueBuffer->c_str());
+  char* pValueBuffer = valueBuffer->data();
   for (const std::unique_ptr<DictEntry>& entry : *lexicon) {
     for (const auto& value : entry->Values()) {
       strcpy(pValueBuffer, value.c_str());
@@ -131,5 +131,5 @@ void SerializedValues::ConstructBuffer(std::string* valueBuffer,
       pValueBuffer += value.length() + 1;
     }
   }
-  assert(valueBuffer->c_str() + *valueTotalLength == pValueBuffer);
+  assert(valueBuffer->data() + *valueTotalLength == pValueBuffer);
 }
diff --git a/src/UTF8Util.hpp b/src/UTF8Util.hpp
index 6babd3674..f1db415b6 100644
--- a/src/UTF8Util.hpp
+++ b/src/UTF8Util.hpp
@@ -158,7 +158,7 @@ class OPENCC_EXPORT UTF8Util {
   static std::string FromSubstr(const char* str, size_t length) {
     std::string newStr;
     newStr.resize(length);
-    strncpy(const_cast<char*>(newStr.c_str()), str, length);
+    strncpy(newStr.data(), str, length);
     return newStr;
   }
 
diff --git a/src/tools/CommandLine.cpp b/src/tools/CommandLine.cpp
index bfbd64b03..96c0fa41a 100644
--- a/src/tools/CommandLine.cpp
+++ b/src/tools/CommandLine.cpp
@@ -16,6 +16,7 @@
  * limitations under the License.
  */
 
+#include <cstring>
 #include <fstream>
 
 #ifdef _WIN32