update doc
diff --git a/cpp/cpptutorial.md b/cpp/cpptutorial.md
index c6a1690..c19b472 100644
--- a/cpp/cpptutorial.md
+++ b/cpp/cpptutorial.md
@@ -252,8 +252,7 @@
 
 ```cpp
  public:
-  RouteGuideClient(std::shared_ptr<ChannelInterface> channel,
-                   const std::string& db)
+  RouteGuideClient(std::shared_ptr<Channel> channel, const std::string& db)
       : stub_(RouteGuide::NewStub(channel)) {
     ...
   }