Understanding Dates

[grumbachr]

I've been working with dates recently and I've wondering about a few things. In FileMaker when a field is defined as being a date are the following true;

10/5/71 = 10/05/1971

and if that is true what about

10/5/71 = 10/5/2071

This is more of curiosity than anything.

[comment]

Do not confuse the way a date is DISPLAYED with what it truly is.

10/5/71 = 10/05/1971

might be true or false, depending on what's actually stored in the field - which you should see if you click into it.

[IdealData]

You could test this yourself. Create a date field and just keep feeding it will advancing year numbers.

I found that

1/1/40 is 1/1/1940

31/12/39 is 31/12/2039

so it looks like the "cut off" point is midnight 31/12/2039.

If you want dates prior to 1940 (or after 2039) then the date must be entered in full 4 year format - which you can force in the field definition.

Edited September 4, 2009 by Guest

[comment]

1/1/40 is 1/1/1940

I think a better way to put it would be:

When you enter 1/1/40 into a date field, it will be immediately converted to 1/1/1940.

BTW, the cut-off point is not static - it's always 70 years back from the current year (or 30 years forward).

[IdealData]

Thanks comment. I was curious about that and I remember there were different rules in FM5/6.

[comment]

The reasoning is not too difficult to figure out: it's a convenient compromise between dates of birth and future commitments. I believe Excel does something similar, though perhaps less sophisticated.