code style: Don't use std:: inside .cpp files.
diff --git a/ndn-cpp/security/identity/identity-manager.cpp b/ndn-cpp/security/identity/identity-manager.cpp
index 3faf94b..e9c80bc 100644
--- a/ndn-cpp/security/identity/identity-manager.cpp
+++ b/ndn-cpp/security/identity/identity-manager.cpp
@@ -135,7 +135,7 @@
 
   return certificate;
 #else
-  throw std::runtime_error("not implemented");
+  throw runtime_error("not implemented");
 #endif
 }
 
@@ -185,7 +185,7 @@
 
   return sha256Sig;
 #else
-  throw std::runtime_error("not implemented");
+  throw runtime_error("not implemented");
 #endif
 }
 
@@ -265,7 +265,7 @@
 
   return certificate;
 #else
-  throw std::runtime_error("not implemented");
+  throw runtime_error("not implemented");
 #endif  
 }