diff --git a/src/storage/repo-storage.hpp b/src/storage/repo-storage.hpp
index fe355ad..62d8fa4 100644
--- a/src/storage/repo-storage.hpp
+++ b/src/storage/repo-storage.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019, Regents of the University of California.
+ * Copyright (c) 2014-2022, Regents of the University of California.
  *
  * This file is part of NDN repo-ng (Next generation of NDN repository).
  * See AUTHORS.md for complete list of repo-ng authors and contributors.
@@ -25,8 +25,6 @@
 
 #include <ndn-cxx/util/signal.hpp>
 
-#include <queue>
-
 namespace repo {
 
 /**
@@ -39,14 +37,9 @@
   class Error : public std::runtime_error
   {
   public:
-    explicit
-    Error(const std::string& what)
-      : std::runtime_error(what)
-    {
-    }
+    using std::runtime_error::runtime_error;
   };
 
-public:
   explicit
   RepoStorage(Storage& store);
 
@@ -96,7 +89,7 @@
 
 private:
   Storage& m_storage;
-  const int NOTFOUND = -1;
+  static constexpr int NOTFOUND = -1;
 };
 
 } // namespace repo
diff --git a/src/storage/sqlite-storage.hpp b/src/storage/sqlite-storage.hpp
index 217f9d0..6c6006d 100644
--- a/src/storage/sqlite-storage.hpp
+++ b/src/storage/sqlite-storage.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019, Regents of the University of California.
+ * Copyright (c) 2014-2022, Regents of the University of California.
  *
  * This file is part of NDN repo-ng (Next generation of NDN repository).
  * See AUTHORS.md for complete list of repo-ng authors and contributors.
@@ -22,33 +22,17 @@
 
 #include "storage.hpp"
 
-#include <algorithm>
-#include <iostream>
-#include <queue>
-#include <stdlib.h>
-#include <string>
 #include <sqlite3.h>
-#include <vector>
 
 namespace repo {
 
 class SqliteStorage : public Storage
 {
 public:
-  class Error : public std::runtime_error
-  {
-  public:
-    explicit
-    Error(const std::string& what)
-      : std::runtime_error(what)
-    {
-    }
-  };
-
   explicit
   SqliteStorage(const std::string& dbPath);
 
-  ~SqliteStorage();
+  ~SqliteStorage() override;
 
   /**
    *  @brief  put the data into database
@@ -92,7 +76,6 @@
   std::string m_dbPath;
 };
 
-
 } // namespace repo
 
 #endif // REPO_STORAGE_SQLITE_STORAGE_HPP
diff --git a/src/storage/storage.hpp b/src/storage/storage.hpp
index d724eb1..abda77c 100644
--- a/src/storage/storage.hpp
+++ b/src/storage/storage.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2019, Regents of the University of California.
+ * Copyright (c) 2014-2022, Regents of the University of California.
  *
  * This file is part of NDN repo-ng (Next generation of NDN repository).
  * See AUTHORS.md for complete list of repo-ng authors and contributors.
@@ -21,26 +21,19 @@
 #define REPO_STORAGE_STORAGE_HPP
 
 #include "../common.hpp"
-#include <string>
-#include <iostream>
-#include <stdlib.h>
 
 namespace repo {
 
 /**
-  * @brief Storage is a virtual abstract class which will be called by SqliteStorage
-  */
+ * @brief Storage is a virtual abstract class which will be called by SqliteStorage
+ */
 class Storage : noncopyable
 {
 public:
   class Error : public std::runtime_error
   {
   public:
-    explicit
-    Error(const std::string& what)
-      : std::runtime_error(what)
-    {
-    }
+    using std::runtime_error::runtime_error;
   };
 
 public: