user4597: I'd like to get a TCP based connection from an arduino to a node.JS server. I found an example, I've tried to run it but its throwing the errors below, would appreciate any help.
Error Messages
    Arduino: 1.6.6 Hourly Build 2015/09/24 05:43 (Windows 7), Board: "Arduino/Genuino Uno"
WARNING: Category '' in library ArduinoJson is not valid. Setting to 'Uncategorized'
socketio.ino: In function 'void hello(Client&, const char*)':

socketio:19: error: expected unqualified-id before '.' token

socketio.ino: In function 'void setup()':

socketio:38: error: invalid conversion from 'void (*)(Client&, const char*)' to 'void (*)(Client&, ArduinoJson::JsonArray&)' [-fpermissive]

In file included from socketio.ino:6:0:

C:\arduino_1.6.6\libraries\socket.io-arduino-client.2/SocketIOClient.h:56:8: error:   initializing argument 2 of 'void SocketIOClient::setEventHandler(const char*, void (*)(Client&, ArduinoJson::JsonArray&))' [-fpermissive]

   void setEventHandler(const char* eventName, void (*handler)(Client& client, JsonArray& data));

        ^

socketio:39: error: invalid conversion from 'void (*)(Client&, const char*)' to 'void (*)(Client&, ArduinoJson::JsonArray&)' [-fpermissive]

In file included from socketio.ino:6:0:

C:\arduino_1.6.6\libraries\socket.io-arduino-client.2/SocketIOClient.h:56:8: error:   initializing argument 2 of 'void SocketIOClient::setEventHandler(const char*, void (*)(Client&, ArduinoJson::JsonArray&))' [-fpermissive]

   void setEventHandler(const char* eventName, void (*handler)(Client& client, JsonArray& data));

        ^

exit status 1
expected unqualified-id before '.' token

  This report would have more information with
  "Show verbose output during compilation"
  enabled in File > Preferences.

Arduino Code
    #include 
    #include 
#include <ArduinoJson.h>
#include <SocketIOClient.h>

EthernetClient ethClient;
SocketIOClient client(ethClient);

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
char hostname[] = "192.168.100.40";
int port = 3000;

// Socket.io "hello" EVENT handler
void hello(Client& client, char const * data) {
    Serial.print("[hello] event happening: ");
    Serial.println(data);
    Client.emit("goodbye", "Arduino here, goodbye!");
}

// Socket.io "goodbye" EVENT handler
void goodbye(Client& client, char const * data) {
    Serial.print("[goodbye] event happening: ");
    Serial.println(data);
    Serial.println("That is all.");
}

void setup() {
    Serial.begin(9600);
    Ethernet.begin(mac);

    if(!client.connect(hostname, port)) {
        Serial.println(F("Not connected."));
    }

    //Event hanlders
    client.setEventHandler("hello", hello);
    client.setEventHandler("goodbye", goodbye);

    //Say hello to the server
    client.emit("hello", "Arduino here, hello!");
}

void loop() {
    client.monitor();
}

SocketIO.h
/*
    socket.io-arduino-client: a Socket.IO client for the Arduino

    Based on Bill Roy's Arduino Socket.IO Client (which is based on 
    Kevin Rohling's Arduino WebSocket Client) with event handling by
    @dantaex

    Copyright 2014 Quentin Pigné

    Permission is hereby granted, free of charge, to any person
    obtaining a copy of this software and associated documentation
    files (the "Software"), to deal in the Software without
    restriction, including without limitation the rights to use,
    copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following
    conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
    OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
    OTHER DEALINGS IN THE SOFTWARE.
*/

#ifndef SocketIOClient_H
#define SocketIOClient_H

#include <Arduino.h>
#include <Client.h>
#include <SPI.h>

#include <ArduinoJson.h>

#include "HashMap.h"

//Length of static data buffers
#define DATA_BUFFER_LEN 200
#define SID_LEN 24

//Max size of the HashTable
#define HASH_SIZE 20

class SocketIOClient {
    public:
        SocketIOClient(Client& client);
        //Public connection methods
        bool connect(const char* hostname, int port = 80, const char* resource = "socket.io", const char* nsp = "/");
        //Public event handling methods
        void setEventHandler(const char* eventName, void (*handler)(Client& client, JsonArray& data));
        //Public data emitting methods
        void emit(const char* event, const char* data);
        //Monitoring for incoming data
        void monitor();

    private:
        //Connection attributes
        Client& client;
        char* hostname;
        int port;
        char* resource;
        char* nsp;
        char sid[SID_LEN];
        //Incoming data reading attributes
        char databuffer[DATA_BUFFER_LEN];
        char* dataptr;
        //Event handling attributes
        int nbEvent;
        static HashType<const char*, void(*)(Client& client, JsonArray& data)> hashRawArray[HASH_SIZE];
        static HashMap<const char*, void(*)(Client& client, JsonArray& data)> eventHandlers;

        //Private incoming data reading methods
        bool waitForInput();
        void eatHeader();
        void readInput();
};

#endif


user4143: Make your char * parameters const char *.

4597: <p>I'd like to get a TCP based connection from an arduino to a node.JS server. I found an example, I've tried to run it but its throwing the errors below, would appreciate any help.</p>

<p>Error Messages
    Arduino: 1.6.6 Hourly Build 2015/09/24 05:43 (Windows 7), Board: "Arduino/Genuino Uno"</p>

<pre><code>WARNING: Category '' in library ArduinoJson is not valid. Setting to 'Uncategorized'
socketio.ino: In function 'void hello(Client&amp;, const char*)':

socketio:19: error: expected unqualified-id before '.' token

socketio.ino: In function 'void setup()':

socketio:38: error: invalid conversion from 'void (*)(Client&amp;, const char*)' to 'void (*)(Client&amp;, ArduinoJson::JsonArray&amp;)' [-fpermissive]

In file included from socketio.ino:6:0:

C:\arduino_1.6.6\libraries\socket.io-arduino-client.2/SocketIOClient.h:56:8: error:   initializing argument 2 of 'void SocketIOClient::setEventHandler(const char*, void (*)(Client&amp;, ArduinoJson::JsonArray&amp;))' [-fpermissive]

   void setEventHandler(const char* eventName, void (*handler)(Client&amp; client, JsonArray&amp; data));

        ^

socketio:39: error: invalid conversion from 'void (*)(Client&amp;, const char*)' to 'void (*)(Client&amp;, ArduinoJson::JsonArray&amp;)' [-fpermissive]

In file included from socketio.ino:6:0:

C:\arduino_1.6.6\libraries\socket.io-arduino-client.2/SocketIOClient.h:56:8: error:   initializing argument 2 of 'void SocketIOClient::setEventHandler(const char*, void (*)(Client&amp;, ArduinoJson::JsonArray&amp;))' [-fpermissive]

   void setEventHandler(const char* eventName, void (*handler)(Client&amp; client, JsonArray&amp; data));

        ^

exit status 1
expected unqualified-id before '.' token

  This report would have more information with
  "Show verbose output during compilation"
  enabled in File &gt; Preferences.
</code></pre>

<p>Arduino Code
    #include 
    #include </p>

<pre><code>#include &lt;ArduinoJson.h&gt;
#include &lt;SocketIOClient.h&gt;

EthernetClient ethClient;
SocketIOClient client(ethClient);

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
char hostname[] = "192.168.100.40";
int port = 3000;

// Socket.io "hello" EVENT handler
void hello(Client&amp; client, char const * data) {
    Serial.print("[hello] event happening: ");
    Serial.println(data);
    Client.emit("goodbye", "Arduino here, goodbye!");
}

// Socket.io "goodbye" EVENT handler
void goodbye(Client&amp; client, char const * data) {
    Serial.print("[goodbye] event happening: ");
    Serial.println(data);
    Serial.println("That is all.");
}

void setup() {
    Serial.begin(9600);
    Ethernet.begin(mac);

    if(!client.connect(hostname, port)) {
        Serial.println(F("Not connected."));
    }

    //Event hanlders
    client.setEventHandler("hello", hello);
    client.setEventHandler("goodbye", goodbye);

    //Say hello to the server
    client.emit("hello", "Arduino here, hello!");
}

void loop() {
    client.monitor();
}
</code></pre>

<p>SocketIO.h</p>

<pre><code>/*
    socket.io-arduino-client: a Socket.IO client for the Arduino

    Based on Bill Roy's Arduino Socket.IO Client (which is based on 
    Kevin Rohling's Arduino WebSocket Client) with event handling by
    @dantaex

    Copyright 2014 Quentin Pigné

    Permission is hereby granted, free of charge, to any person
    obtaining a copy of this software and associated documentation
    files (the "Software"), to deal in the Software without
    restriction, including without limitation the rights to use,
    copy, modify, merge, publish, distribute, sublicense, and/or sell
    copies of the Software, and to permit persons to whom the
    Software is furnished to do so, subject to the following
    conditions:

    The above copyright notice and this permission notice shall be
    included in all copies or substantial portions of the Software.

    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
    EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
    OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
    NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
    HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
    WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
    FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
    OTHER DEALINGS IN THE SOFTWARE.
*/

#ifndef SocketIOClient_H
#define SocketIOClient_H

#include &lt;Arduino.h&gt;
#include &lt;Client.h&gt;
#include &lt;SPI.h&gt;

#include &lt;ArduinoJson.h&gt;

#include "HashMap.h"

//Length of static data buffers
#define DATA_BUFFER_LEN 200
#define SID_LEN 24

//Max size of the HashTable
#define HASH_SIZE 20

class SocketIOClient {
    public:
        SocketIOClient(Client&amp; client);
        //Public connection methods
        bool connect(const char* hostname, int port = 80, const char* resource = "socket.io", const char* nsp = "/");
        //Public event handling methods
        void setEventHandler(const char* eventName, void (*handler)(Client&amp; client, JsonArray&amp; data));
        //Public data emitting methods
        void emit(const char* event, const char* data);
        //Monitoring for incoming data
        void monitor();

    private:
        //Connection attributes
        Client&amp; client;
        char* hostname;
        int port;
        char* resource;
        char* nsp;
        char sid[SID_LEN];
        //Incoming data reading attributes
        char databuffer[DATA_BUFFER_LEN];
        char* dataptr;
        //Event handling attributes
        int nbEvent;
        static HashType&lt;const char*, void(*)(Client&amp; client, JsonArray&amp; data)&gt; hashRawArray[HASH_SIZE];
        static HashMap&lt;const char*, void(*)(Client&amp; client, JsonArray&amp; data)&gt; eventHandlers;

        //Private incoming data reading methods
        bool waitForInput();
        void eatHeader();
        void readInput();
};

#endif
</code></pre>
 4143: <p>Make your <code>char *</code> parameters <code>const char *</code>.</p>
