Count elapsed days using Time.Lib

Using Arduino Programming Questions
#1

I need to set an alarm which will trigger 250 days set. I am using the Time.Lib and looking through the document found this:

#define elapsedDays(_time_) ((_time_) / SECS_PER_DAY)  // this is number of days since Jan 1 1970

The way I plan to count the days would be to create a variable to initially store the start of the daycount and do something like this

if (elapsedDays () - previouselapsedDays >= 250)
{
//DO SOMTHING
}
the problem is when i did do this it was not compiling, which lead me to believe I cant just use elapsedDays as I have.

Can anybody shed some light?

#2

You have to provide the argument to elapsedDays()

#3

Altogether, this seems very fragile.
I’d be saving the start date in EEPROM, that way, even if the board is restarted accidentally, you’ll have a reference to the elapsed duration.

It would be a pity to wait 250 days to find you missed a restart !

#4

Ok..
But do I have to declare the elapsedDays like this:

unsigned long elapsedDays = (time) ((time) / SECS_PER_DAY);

or something to that effect. Am I right in saying the there is no function elapsedDays() in the Time.Lib

#5

Wrong.

I think you want something like this

static unsigned long startDay = elapsedDays(now())
if(elapsedDays(now()) - startDay >=250)
{
   startDay = elapsedDays(now())
   //perform task
}

The suggestion of getting startDay stored in eeprom is very good.

#6

Thanks for that and yes storing the value to eeprom is a good idea