C++ - 嘗試使用模板時出現錯誤

Question

我是新來的C++，並且正在使用模板。 我有一個可以獲得某種類型的函數。

頭：

template <typname T> 
response_t send_sequence_to_device(map<const string_t, T*> msg2device_p, 
    vector<response_t>& result_list, ushort num_attempts=SEND_NUM_ATTEMPTS); 

來源：

template <typname T> 
response_t send_sequence_to_device(map<const string_t, T*> msg2device_p, 
    vector<response_t>& result_list, ushort num_attempts) 
{ 
    bool is_ok_flag = true; 
    response_t r; 
    raftor1_logs_t* rlogs; 
    map<const string_t, T*>::iterator msg_it; 
    for(msg_it=msg2device_p.begin(); msg_it!=msg2device_p.end() and is_ok_flag; msg_it++) 
    { 
     r = msg_it->second->send(msg_it->first, true, num_attempts); 
     result_list.push_back(r); 
     is_ok_flag = is_ok_flag and is_ok(r); 

     if(not(is_ok_flag)) 
     { 
      stringstream ss; 
      ss << "ALERT: Sequence aborted due to error on message [" << msg_it->first << "] "; 
      if(r.erred()) 
       ss << "due to communication failure."; 
      else 
       ss << "with error message [" << r.msg << "]."; 
      rlogs->alert.begin_record(); 
      rlogs->alert.write(ss.str()); 
      rlogs->alert.end_record(); 
     } 
    } 

    if(is_ok_flag) 
     r.set_ok("ok.\n"); 

    return r; 
} 

我得到以下錯誤：

device_manager.cpp|1076|error: need 'typename' before 'std::map, T*>::iterator' because 'std::map, T*>' is a dependent scope

Answer 1

這裏：

map<const string_t, T*>::iterator msg_it; 

你需要這個：

typename map<const string_t, T*>::iterator msg_it;