diff --git a/core/common.hpp b/core/common.hpp
index 34da654..614dd4e 100644
--- a/core/common.hpp
+++ b/core/common.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2021,  Regents of the University of California,
+ * Copyright (c) 2014-2022,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -46,6 +46,7 @@
 #include <memory>
 #include <stdexcept>
 #include <string>
+#include <string_view>
 #include <utility>
 #include <vector>
 
diff --git a/core/version.cpp.in b/core/version.cpp.in
index 8abef00..04fd901 100644
--- a/core/version.cpp.in
+++ b/core/version.cpp.in
@@ -19,10 +19,8 @@
 
 #include "core/version.hpp"
 
-namespace ndn {
-namespace tools {
+namespace ndn::tools {
 
 const char VERSION[] = "@VERSION_BUILD@";
 
-} // namespace tools
-} // namespace ndn
+} // namespace ndn::tools
diff --git a/core/version.hpp b/core/version.hpp
index 03058f6..2a20a1a 100644
--- a/core/version.hpp
+++ b/core/version.hpp
@@ -22,15 +22,13 @@
 
 #include "core/common.hpp"
 
-namespace ndn {
-namespace tools {
+namespace ndn::tools {
 
 /**
  * \brief The version of ndn-tools.
  */
 extern const char VERSION[];
 
-} // namespace tools
-} // namespace ndn
+} // namespace ndn::tools
 
 #endif // NDN_TOOLS_CORE_VERSION_HPP