My gRPC source file can't read grpc's service

Question

This is my .proto file

syntax = "proto3";

package helloworld;

service Greeter {
  // Sends a greeting
  rpc SayHello (HelloRequest) returns (HelloReply) {}
  // Sends another greeting
  rpc SayHelloAgain (HelloRequest) returns (HelloReply) {}
}

// The request message containing the user's name.
message HelloRequest {
  string name = 1;
}

// The response message containing the greetings
message HelloReply {
  string message = 1;
}

I declared service and messages here. And I made cc file and header file by protoc.exe I followed gRPC c++ Tutorial, and i wrote greeter_server.cc

But geeter_server.cc file can't read service Greeter. But it can read variable of Messages What is the problem?

I included header file well, And i searched google but i can't find answer help me please