include the mbed library with this snippet

#include "mbed.h"
#include "rtos.h"

// change this to 0 to output messages to serial instead of LCD
#define USE_LCD 0

#define MQTTCLIENT_QOS2 1

#include "easy-connect.h"
#include "MQTTNetwork.h"
#include "MQTTmbed.h"
#include "MQTTClient.h"

Serial pc(USBTX, USBRX);    // Serial port for Debug messages
Serial enocean(p28, p27);   // tx, rx --> Serial Communication with EnOcean Transiver
DigitalOut led1(LED1); // Connection information LED
DigitalOut led2(LED2);
DigitalOut led3(LED3);

Thread thread_ENOCEAN;

char c[30];
char buf[30];
volatile int i = 0;

// Network and MQTT
const char* hostname = "192.168.10.5";
int port = 1883;
char* topic = "hellomqtt/topic";
int rc;
// generate a unique random Client-ID
char str[20] ="mbed-clientID-0001";

// Interupt Routine to read in data from serial port
void Rx_intt() {
    c[i++] = LPC_UART2->RBR;
    led2 = !led2;
    return;
}

void enocean_thread() {
    enocean.baud(57600);
    enocean.attach(&Rx_intt, Serial::RxIrq);
    i = 0;    
}

int main(int argc, char* argv[])
{
    pc.baud(9600);
    NetworkInterface* network = easy_connect(false);
    MQTTNetwork mqttNetwork(network);
    MQTT::Client<MQTTNetwork, Countdown> client(mqttNetwork);
    rc = mqttNetwork.connect(hostname, port);
    MQTTPacket_connectData data = MQTTPacket_connectData_initializer;
    data.MQTTVersion = 3;    
    str[18] = 0;
    data.clientID.cstring = str;
    rc = client.connect(data);
    led1 = 1;
    MQTT::Message message;
    // Opening thread for Enocean Serial Data
    thread_ENOCEAN.start(enocean_thread);
    
    
    while(1)
    {
        if(!client.isConnected())
        {
            led1 = 0;
            rc = client.disconnect();
            mqttNetwork.disconnect();
            
            network = easy_connect(false);
            MQTTNetwork mqttNetwork(network);
            MQTT::Client<MQTTNetwork, Countdown> client(mqttNetwork);
            rc = mqttNetwork.connect(hostname, port);
            MQTTPacket_connectData data = MQTTPacket_connectData_initializer;
            data.MQTTVersion = 3;    
            str[18] = 0;
            data.clientID.cstring = str;
            rc = client.connect(data);
        }
        
        if(i > 20 && client.isConnected())
        {
            rc = client.connect(data);
            led1 = 1;
            led2 = 0;
            
            memcpy(buf, c, i);
            
            message.qos = MQTT::QOS0;
            message.retained = false;
            message.dup = false;
            message.payload = (void*)buf;
            message.payloadlen = 21;//strlen(buf)+1;
            
            rc = client.publish(topic, message);
            //pc.printf("Length: %i\n",sizeof(buf));
            for(int j=0; j<21;j++)
            {
                pc.putc(buf[j]);
            }
            i = 0;
        }
        //client.yield(100);
    }
}