Getting Incorrect value of submonth in carbon

Question

Please go through the below code

Why getting 3rd month two times instead of 2nd month. Code

('current ' . Carbon::now()->format('Y-m-d'));//2021-04-30
('sub 1 -'.Carbon::now()->subMonths(1)->format('Y-m-d'));
('sub 2 -'.Carbon::now()->subMonths(2)->format('Y-m-d'));
('sub 3 -'.Carbon::now()->subMonths(3)->format('Y-m-d'));

Result

current 2021-04-30
sub 1 - 2021-03-30 
sub 2 - 2021-03-02 
sub 3 - 2021-01-30 

Expected Result

current 2021-04-30 
sub 1 - 2021-03-30 
sub 2 - 2021-02-02 
sub 3 - 2021-01-30 

Millenary

Answer 1

This is actually expected behaviour for Carbon. Carbon uses the PHP DateTime class, and there can be overflow from the addition and subtraction functions.

sub 2 - 2021-03-02 is actually being calculated by the date 2021-02-30, which doesn't exist, therefore overflowing to 2021-03-02.

Take a look here to see the effects https://carbon.nesbot.com/docs/#api-addsub

To fix this behaviour, you can use the addMonthNoOverflow, addMonthsNoOverflow, subMonthNoOverflow and subMonthsNoOverflow methods.

Impressionist

Side note to say, such overflow can sound weird but it's pretty standard, you'll get the same results with date functions in Java, JavaScript, etc. – Gnathion