diff --git a/casbin/logger.cpp b/casbin/logger.cpp
index dd311f0b..b5b56d63 100644
--- a/casbin/logger.cpp
+++ b/casbin/logger.cpp
@@ -10,13 +10,13 @@ namespace casbin {
 
 // Print formats using the default formats for its operands and logs the message.
 template <typename T, typename... Object>
-void Logger::Print(T arg, Object... objects) {
+void Logger::Print(T const& arg, Object const&... objects) {
     return;
 }
 
 // Printf formats according to a format specifier and logs the message.
 template <typename... Object>
-void Logger::Printf(std::string format, Object... objects) {
+void Logger::Printf(std::string const& format, Object const&... objects) {
     Print(objects...);
 }
 
diff --git a/include/casbin/log/Logger.h b/include/casbin/log/Logger.h
index bf3be10f..380db885 100644
--- a/include/casbin/log/Logger.h
+++ b/include/casbin/log/Logger.h
@@ -18,13 +18,13 @@ class Logger {
 
     // Print formats using the default formats for its operands and logs the message.
     template <typename T, typename... Object>
-    void Print(T arg, Object... objects);
+    void Print(T const& arg, Object const&... objects);
 
     // Printf formats according to a format specifier and logs the message.
     template <typename... Object>
-    void Printf(std::string, Object... objects);
+    void Printf(std::string const& format, Object const&... objects);
 };
 
 } // namespace casbin
 
-#endif
\ No newline at end of file
+#endif
diff --git a/include/casbin/log/default_logger.h b/include/casbin/log/default_logger.h
index 9e8e90af..ce7b7f57 100644
--- a/include/casbin/log/default_logger.h
+++ b/include/casbin/log/default_logger.h
@@ -12,14 +12,14 @@ class DefaultLogger : public Logger {
     bool IsEnabled() { return m_enable; }
 
     template <typename... Object>
-    void Print(Object... objects) {
+    void Print(Object const&... objects) {
         if (m_enable) {
             Print(objects...);
         }
     }
 
     template <typename... Object>
-    void Print(std::string format, Object... objects) {
+    void Print(std::string const& format, Object const&... objects) {
         if (m_enable) {
             Printf(format, objects...);
         }
@@ -28,4 +28,4 @@ class DefaultLogger : public Logger {
 
 } // namespace casbin
 
-#endif
\ No newline at end of file
+#endif
diff --git a/include/casbin/log/log_util.h b/include/casbin/log/log_util.h
index c9340679..5a709daf 100644
--- a/include/casbin/log/log_util.h
+++ b/include/casbin/log/log_util.h
@@ -18,17 +18,17 @@ class LogUtil {
 
     // LogPrint prints the log.
     template <typename... Object>
-    static void LogPrint(Object... objects) {
+    static void LogPrint(Object const&... objects) {
         s_logger.Print(objects...);
     }
 
     // LogPrintf prints the log with the format.
     template <typename... Object>
-    static void LogPrintf(std::string format, Object... objects) {
+    static void LogPrintf(std::string const& format, Object const&... objects) {
         s_logger.Printf(format, objects...);
     }
 };
 
 } // namespace casbin
 
-#endif
\ No newline at end of file
+#endif