// Testing if 'time_t' from the TimeLib library is signed or unsigned.
//#include <TimeLib.h>      // PJRC TimeLib

// Testing if 'time_t' from the avr-libc is signed or unsigned.
#include <time.h>

void setup() 
{
  Serial.begin(115200);
  Serial.print("sizeof(time_t) = ");
  Serial.println(sizeof(time_t));

  Serial.println("Testing time_t, a negative number is signed.");
  time_t x = 0xFFFFAAAACCCC3333;
  Serial.println(x);
}

void loop() {}