Return value from function

Projects Programming
1

Hi There,

I'm trying to organize my codes since they are getting longer and longer. I'm trying to use the tabs and so far it going well, till I tried to let a function return a value.

my main file;

#include <SPI.h>
#include <Wire.h>
#include <SD.h>

void setup() {
  Serial.begin(9600);
  Wire.begin();
  //startSD();
  startRTC();
  //startTemp();
}

void loop() {

Serial.println(getTimeDate());

My RTC part is loaded in his own tabfile;

#include <RTClib.h>
RTC_DS1307 rtc;

char buf1[20];

void startRTC(){
  Serial.println("Starting RTC...");
  rtc.begin();
  getTimeDate();
}

void getTimeDate(){
  DateTime now = rtc.now();
  sprintf(buf1, "%02d:%02d:%02d %02d/%02d/%02d",  now.hour(), now.minute(), now.second(), now.day(), now.month(), now.year());  
  return buf1;
}

When runnings this code I get the following error;

"templogger:17: error: invalid use of void expression"

I'm trying to make a function to format for me the time and date and returns this new value.
This function I will use for logger into a .txt file at the SD card.

function getTimeDate() is working fine. Output of buf1 is actually what I want.

I'm tried for days many different approaches to reach my result, but without any luck.
This code looks for me the most logical way to realize what I want.