Compiler errors when playing with members versus references. [Boost asio]

[Stewbond]

Consider this code which works perfectly. It opens a socket and sends a message to an IP and port:

#include <boost/asio.hpp>

struct Client
{
   boost::asio::io_service& io_service;
   boost::asio::ip::tcp::socket socket;

   Client(boost::asio::io_service& svc) 
       : io_service(svc), socket(io_service) 
   {
       boost::asio::ip::tcp::resolver resolver(io_service);
       boost::asio::ip::tcp::resolver::iterator endpoint = resolver.resolve(boost::asio::ip::tcp::resolver::query("127.0.0.1", "32323"));
       boost::asio::connect(this->socket, endpoint);
   }

   void send(std::string const& message) {
       socket.send(boost::asio::buffer(message));
   }
};

int main() 
{
   boost::asio::io_service svc;
   Client client(svc);

   client.send("hello world\n");
   client.send("bye world\n");
}

Next, consider this code. It does the same thing, except the io_service class is now a member of Client as opposed to a reference to some super-instance.

#include <boost/asio.hpp>

struct Client
{
   boost::asio::io_service io_service;
   boost::asio::ip::tcp::socket socket;

   Client() 
       : io_service(), socket(io_service) 
   {
       boost::asio::ip::tcp::resolver resolver(io_service);
       boost::asio::ip::tcp::resolver::iterator endpoint = resolver.resolve(boost::asio::ip::tcp::resolver::query("127.0.0.1", "32323"));
       boost::asio::connect(this->socket, endpoint);
   }

   void send(std::string const& message) {
       socket.send(boost::asio::buffer(message));
   }
};

int main() 
{
   Client client();

   client.send("hello world\n");
   client.send("bye world\n");
}

I can't explain it, but when I try to compile the latter I get:

[stew@Romulus test]$ make client
g++ -o client client.cpp -L/usr/lib -lboost_system -lpthread
client.cpp: In function ‘int main()’:
client.cpp:25:11: error: request for member ‘send’ in ‘client’, which is of non-class type ‘Client()’
    client.send("hello world\n");
           ^~~~
client.cpp:26:11: error: request for member ‘send’ in ‘client’, which is of non-class type ‘Client()’
    client.send("bye world\n");
           ^~~~
make: *** [makefile:8: client] Error 1

Can someone help me to understand the error? Why is the send method suddenly treated as if it wasn't a member? If I make Client a class and put everything in public: I get the same thing.

[coder777]

Because on line 23 you have the prototype of the function client which returns an object of type Client.

So either you omit the () or you change them to {}.

[Stewbond]

Wow, it's the simple mistakes that really get you!

Thanks.