Arduino class implementing TimeLib.h - c++

Question

I'm creating this library for the ESP8266-Arduino that makes use of the TimeLib.h library.
In my header I have:
WiFiUDP *_UdpNTP = NULL;
void setupTime();
time_t getNtpTime();
void sendNTPpacket(WiFiUDP *u);
And these are my functions:
void Konnec::setupTime() {
setSyncProvider(getNtpTime);
setSyncInterval(NTP_POL_TIME);
}
time_t Konnec::getNtpTime() {
//WiFiUDP udp;
//udp.begin(localPort);
_UdpNTP = new WiFiUDP();
_UdpNTP->begin(localPort);
while (_UdpNTP->parsePacket() > 0); // discard any previously received packets
for (int i = 0; i < 5; i++) { // 5 retries.
sendNTPpacket(_UdpNTP);
uint32_t beginWait = millis();
while (millis() - beginWait < 1000) {
if (_UdpNTP->parsePacket()) {
Serial.println("");
Serial.println("Receive NTP Response");
_UdpNTP->read(packetBuffer, NTP_PACKET_SIZE);
// Extract seconds portion.
unsigned long highWord = word(packetBuffer[40], packetBuffer[41]);
unsigned long lowWord = word(packetBuffer[42], packetBuffer[43]);
unsigned long secSince1900 = highWord << 16 | lowWord;
_UdpNTP->flush();
return secSince1900 - 2208988800UL + TIMEZONE * SECS_PER_HOUR;
}
delay(10);
}
}
Serial.println("");
Serial.println("No NTP Response :-(");
return 0; // return 0 if unable to get the time
}
void Konnec::sendNTPpacket(WiFiUDP *u) {
// Zeroise the buffer.
memset(packetBuffer, 0, NTP_PACKET_SIZE);
memcpy(packetBuffer, sendBuffer, 16);
if (u->beginPacket(timeServer, 123)) {
u->write(packetBuffer, NTP_PACKET_SIZE);
u->endPacket();
}
}
And this is the error I get:
konnec.cpp: 991:28: error: cannot convert 'Konnec::getNtpTime' from type 'time_t (Konnec::)() {aka long int (Konnec::)()}' to type 'getExternalTime {aka long int (*)()}
setSyncProvider(getNtpTime)
Error compiling libraries
Any knows what would be the solution?

Answer 1

The problem seems to be that Konnec::getNtpTime is a class method, and yet setSyncProvider expects a function. A function and a method are different things remember, as a method also needs to know the specific class instance it is operating on.
Looking through your code though, it looks like getNtpTime doesn't rely on anything specific to your class, so you could declare it as:
static time_t Konnec::getNtpTime();
which will let it be used as a function, as it effectively is at that point.