subtraction of error months in 31 days (strtotime)

Question

I’m developing a graph using the library chart.js. It is working perfectly. It happens that today, the month of May with 31 days, the subtractions of the months happens in the wrong way.

$mhoje = date("M");

$m1 = date('M', strtotime(' - 1 month'));
$em1 = ucfirst(strftime('%b', strtotime($m1)));

echo "$mhoje / $m1 / $em1"; // May / May / Mai

That is to say, hoje menos 1 month it’s still May.

I use only date("M") because I only need the name of the month and not the dates, but I have already tested complete, as date("Y-M-d").

Other days it works perfectly.

I need to get the last 12 months from today’s date.

Answer 1

According to the documentation: https://www.php.net/manual/en/datetime.formats.relative.php

To get the last day of a month you must use last day, you can see in the documentation link where this spelled "Day-based Notations", or below:

Format	Description	Exams
yesterday	Midnight of last night	yesterday 14:00
midnight	Time is set to 00:00:00
today	Time is set to 00:00:00
now	Now - this is simply ignored
noon	Time is set to 12:00:00	yesterday noon
tomorrow	Midnight of tomorrow
back of hour	15 minutes after the reported time	back of 7pm, back of 15
front of hour	15 minutes before the reported time	front of 5am, front of 23
first day of	Set the day to the first day of the current month. This phrase is best used, along with a month name.	first day of January 2008
last day of	Sets the day for the last of the current month. This phrase is best used, along with a month name.	last day of next month
ordinal space dayname space of	Calculates the ordinal number x-th of the current month week.	first sat of July 2008
last space dayname space of	Calculate the last day of the week of the current month.	last sat of July 2008
number space? (unit | 'week')	Handles relative portions of time where the value is a number.	+5 weeks, 12 day, -7 weekdays
ordinal space Unit	Handles relative portions of time where the value is a text.	fifth day, second month
ago	Denies all values of previous relative portions of time.	2 days ago, 8 days ago 14:00, 2 months 5 days ago, 2 months ago 5 days, 2 days ago
dayname	Move to the next day of this name.	Monday
reltext space week	Manipulates the special format weekday + last/this/next week.	Monday next week

And to get the previous month you must use previous month, in the documentation locates where it is written Used Symbols, or below:

Description	Format
dayname	sunday | monday | tuesday | wednesday | thursday | friday | saturday | sun | mon | tue | wed | thu | fri | sat
daytext	weekday | weekdays
number	[+-]?[0-9]+
ordinal	first | second | third | fourth | fifth | sixth | seventh | eighth | ninth | tenth | eleventh | twelfth | next | last | previous | this
reltext	next | last | previous | this
space	[ \t]+
Unit	(('sec' | 'second' | 'min' | 'minute' | 'hour' | 'day' | 'fortnight' | 'forthnight' | 'month' | 'year') 's'?) | weeks | daytext

Soon you can combine both in:

last day of previous month

Translating, "the last day of the previous month". The use of -1 month should be due to considering 30 days as the unit of value, see the online test: https://ideone.com/CwMD39