Object assignment - invalid use of member function error

Question

I have a class which includes among its members an object of another class.

The header file looks like this:

class LinxArduinoEthernetListener : public LinxListener
{
   EthernetServer ArduinoTcpServer(uint16_t);

Where EthernetServer is itself a class (defined in the Arduino EthernetServer.h library).

Because I do not know the port at compile time, but the server object should be a member of the listener class, I allow the server object to be initialized in the class constructor, and then attempt to reassign that object later, using the following code (in the corresponding .cpp file):

ArduinoTcpServer = EthernetServer(port);

Where "port" is a uint16_t. As far as I know, this is the correct way to reassign to an object variable a newly constructed instance.

And yet, the compiler gives me the following error:

LinxArduinoEthernetListener.cpp:122: error: invalid use of member function (did you forget the '()' ?)

ArduinoTcpServer = EthernetServer((uint16_t)port);

I think this may be related to the error I get for the immediately subsequent function call:

LinxArduinoEthernetListener.cpp:123: error: '((LinxArduinoEthernetListener*)this)->LinxArduinoEthernetListener::ArduinoTcpServer' does not have class type

ArduinoTcpServer.begin();

But I would say it clearly does have a class type, namely the EthernetServer class, as specified in the header file.

What am I doing wrong here?

typo: change to `EthernetServer ArduinoTcpServer(some_value);` — eyllanesc, Jul 13 '18 at 19:13
When declaring an object you must put the values, not the types. — eyllanesc, Jul 13 '18 at 19:14
If you are going to initialize it in the constructor then create a pointer: `EthernetServer *ArduinoTcpServer;` and in the constructor: `ArduinoTcpServer = new EthernetServer(some_port)` — eyllanesc, Jul 13 '18 at 19:15
I wish I could call for arbitration on your -1. It's a well-formed question, and I assume that you presume I didn't try that. Declaring it as "EthernetServer ArduinoTcpServer(22);" gives another compiler error: expected identifier before numeric constant EthernetServer ArduinoTcpServer(22); error: expected ',' or '...' before numeric constant — Marshall Eubanks, Jul 13 '18 at 19:18
Also "new" isn't implemented by default in AVR gcc. Therefore I'd rather avoid it. — Marshall Eubanks, Jul 13 '18 at 19:21
Perhaps you shouldn't answer if you don't know what you're talking about. You definitely shouldn't be handing out -1s when can't even give contextually valid suggestions. — Marshall Eubanks, Jul 13 '18 at 19:29
I have used arduino and I have implemented several libraries, and I have used many times `new`, so I say that I find it strange what you mention. In addition, `new` is part of all the C ++ standards — eyllanesc, Jul 13 '18 at 19:32
"new" is defined in the Arduino libraries, but not in AVR gcc. I'd rather avoid using the library since I don't actually need dynamic allocation for its own sake here. https://stackoverflow.com/questions/16274451/operator-new-for-arduino — Marshall Eubanks, Jul 13 '18 at 19:37
but then you must clearly indicate that you are using AVR gcc, in your question you only point arduino. I'm not a fortune teller, I'm not in your mind. :) — eyllanesc, Jul 13 '18 at 19:41

Sid S · Answer 1 · 2018-07-13T19:30:10.847

2

EthernetServer ArduinoTcpServer(uint16_t); declares a member function named ArduinoTcpServer. To declare a member variable, omit the parameter type and parentheses. Also add a constructor to initialize the member variable, e.g. :

class LinxArduinoEthernetListener : public LinxListener
{
    public:
        EthernetServer ArduinoTcpServer;

        LinxArduinoEthernetListener(uint16_t port)
        : ArduinoTcpServer(port)
        {
        }
};

edited Jul 13 '18 at 19:30

answered Jul 13 '18 at 19:24

Sid S

6,037
2
18
24

Thanks, I was trying to remember how to do it this way, but my google-fu was failing me. – Marshall Eubanks Jul 13 '18 at 19:39

score 1 · Answer 2 · answered Jul 13 '18 at 19:33

So, the issue was the declaration of the server object.

Initially, I had it declared as follows:

EthernetServer ArduinoTcpServer(22);

But I would get an error about "expected identifier before numeric constant" referring to the 22. So I googled it, and found someone suggesting that (in some context I don't remember) specifying only the type was sufficient to call the constructor matching that prototype. Doing so allowed the compiler to continue, so I assumed that was valid. However, it seems not.

The real issue is that the compiler Arduino IDE uses requires braces initialization, e.g.

EthernetServer ArduinoTcpServer{22};

That seems to work.

Object assignment - invalid use of member function error

2 Answers2