Hi,
This is my first post, first Arduiono and first project! I've been programming a central heating controller with an ATMEGA 1280, LCD screen and an ethernet shield. The idea is that the scheduler program is a PHP script which runs at regular intervals (on a web server somewhere in California) and this sends commands to the Arduino via HTTP requests. It's been a fun and rewarding challengeso far and I've enjoyed making a working basic prototype; i.e. controlling an LED on the Arduino by sending commands from the server using the PHP CURL library. 
I've been cobbling code together and trying to do the sensible thing by keep everything neat and tidy using classes. I have written an NTP time class which wraps up some of the functionality used in the standard Time library but am having trouble with setSyncProvider(). I can see that the function expects a function but on complie. I get the following error:
NTPTime.cpp: In member function 'void NTPTime::retrieve()':
NTPTime.cpp:25: error: argument of type 'time_t (NTPTime::)()' does not match 'time_t (*)()'
My function void NTPTime::retrieve() sets stuff up.
I'd be grateful for any pointers here on what I'm doing wrong. I'm from the world of VB.NET. 
Thanks!
p.s. the screen will be for showing off (GLCD lib): displaying the current whether using the google weather web service, current news using BBC news RSS (TinyXML lib), current time using NTP, etc. I'll post my results when complete
// HEADER
#ifndef NTPTime_h
#define NTPTime_h
#include "WProgram.h"
#include <Time.h>
#define NTP_PACKET_SIZE 48
// typedef time_t(*getExternalTime)();
class NTPTime {
public:
NTPTime();
void retrieve();
char* time();
char* date();
private:
time_t getNTPTime();
void sendNTPpacket(byte*);
unsigned int _localPort;
byte _timeServer[4];
byte _packetBuffer[NTP_PACKET_SIZE];
};
#endif
#include "WProgram.h"
#include "NTPTime.h"
#include <Udp.h>
#include <Time.h>
// Constructor
NTPTime::NTPTime(){
_timeServer[0] = 194; //{ 194, 35, 252, 7 }
_timeServer[1] = 35;
_timeServer[2] = 252;
_timeServer[3] = 7;
_localPort = 8888;
Udp.begin(_localPort);
}
// Retrieive NTP time from server NTPTime::
void NTPTime::retrieve(){
setSyncProvider(getNTPTime); // I fail here :(
while(timeStatus() == timeNotSet);
}
// Return current time 00:00:00
char* NTPTime::time(){
static char buf[9];
sprintf(buf, "%02d:%02d:%02d\0", hour(), minute(), second());
return buf;
}
// Return current date
char* NTPTime::date(){
static char buf[30];
char _day[10];
char _month[10];
strcpy(_day, dayStr(weekday()));
strcpy(_month, monthShortStr(month()));
sprintf(buf, "%s %d %s %d\0", _day, day(), _month, year());
return buf;
}
/***** Private functions *********/
// Retrieve NTP time
time_t NTPTime::getNTPTime(){
sendNTPpacket(_timeServer); // send an NTP packet to a time server
// wait to see if a reply is available
delay(1000);
if (Udp.available()) {
Udp.readPacket(_packetBuffer, NTP_PACKET_SIZE); // read the packet into the buffer
//the timestamp starts at byte 40 of the received packet and is four bytes,
// or two words, long. First, esxtract the two words:
unsigned long highWord = word(_packetBuffer[40], _packetBuffer[41]);
unsigned long lowWord = word(_packetBuffer[42], _packetBuffer[43]);
// combine the four bytes (two words) into a long integer
// this is NTP time (seconds since Jan 1 1900):
unsigned long secsSince1900 = highWord << 16 | lowWord;
// Unix time starts on Jan 1 1970. In seconds, that's 2208988800:
const unsigned long seventyYears = 2208988800UL;
// subtract seventy years:
unsigned long epoch = secsSince1900 - seventyYears;
return epoch;
}
return 0;
}
// send an NTP request to the time server at the given address
void NTPTime::sendNTPpacket(byte *address){
// set all bytes in the buffer to 0
memset(_packetBuffer, 0, NTP_PACKET_SIZE);
// Initialize values needed to form NTP request
// (see URL above for details on the packets)
_packetBuffer[0] = 0b11100011; // LI, Version, Mode
_packetBuffer[1] = 0; // Stratum, or type of clock
_packetBuffer[2] = 6; // Polling Interval
_packetBuffer[3] = 0xEC; // Peer Clock Precision
// 8 bytes of zero for Root Delay & Root Dispersion
_packetBuffer[12] = 49;
_packetBuffer[13] = 0x4E;
_packetBuffer[14] = 49;
_packetBuffer[15] = 52;
// all NTP fields have been given values, now
// you can send a packet requesting a timestamp:
Udp.sendPacket(_packetBuffer, NTP_PACKET_SIZE, address, 123); //NTP requests are to port 123
}
My C skills are lacking here. I even tried initialising my static object with 
If that doesn't work then I'll have to make all the members and variables shared. I'm hoping that'll work at the minimum otherwise it's all going into the main body of code and that would be a shame!