DateTime perhaps overwritten while during nested for loop-CodePudding

I hope someone can help with this, i think perhaps the issue is i am overwriting the DateTime value in my second for loop, because its not outputting correct values, but not entirely sure.

<?php

$begin_from = new DateTime( "2023-01-01" );
$end_from   = new DateTime( "2023-12-31" );

$begin_to = new DateTime( "2023-01-31" );
$end_to   = new DateTime( "2023-12-31" );

for($i = $begin_from; $i <= $end_from; $i->modify(' 1 month')){
    for($k = $begin_to; $k <= $end_to; $k->modify('first day of')->modify(' 1 month')->modify('last day of')){
    echo $i->format("Y-m-d"),'..',$k->format("Y-m-d");
    echo "\n";
    }
}

From the code above its outputting this:

2023-01-01..2023-01-31
2023-01-01..2023-02-28
2023-01-01..2023-03-31
2023-01-01..2023-04-30
2023-01-01..2023-05-31
2023-01-01..2023-06-30
2023-01-01..2023-07-31
2023-01-01..2023-08-31
2023-01-01..2023-09-30
2023-01-01..2023-10-31
2023-01-01..2023-11-30
2023-01-01..2023-12-31

But, if you run these for loops separately you will get the correct values like below.

2023-01-01..2023-01-31
2023-02-01..2023-02-28
2023-03-01..2023-03-31
2023-04-01..2023-04-30
2023-05-01..2023-05-31
2023-06-01..2023-06-30
2023-07-01..2023-07-31
2023-08-01..2023-08-31
2023-09-01..2023-09-30
2023-10-01..2023-10-31
2023-11-01..2023-11-30
2023-12-01..2023-12-31

Can anyone tell what i am doing wrong here?

CodePudding user response：

I'm not sure why your code produces that output, but it can be simplified using a while loop. You just need one date to manually modify within each loop, and one target date (DateTimeImmutable is recommended for datetimes that are meant to remain unchanged)

$i_date = new DateTime( "2023-01-01" );
$end_date = new DateTimeImmutable( "2023-12-31" );


while($i_date <= $end_date){
    // echo first of month..
    echo $i_date->format("Y-m-d..");
    // goto last of month
    $i_date->modify('last day of');
    // echo last of month \n
    echo $i_date->format("Y-m-d") . "\n";

    // goto first of next month for the next iteration
    $i_date->modify('first day of')->modify(' 1 month');
}

The above will produce the following in PHP v7 :

2023-01-01..2023-01-31
2023-02-01..2023-02-28
2023-03-01..2023-03-31
2023-04-01..2023-04-30
2023-05-01..2023-05-31
2023-06-01..2023-06-30
2023-07-01..2023-07-31
2023-08-01..2023-08-31
2023-09-01..2023-09-30
2023-10-01..2023-10-31
2023-11-01..2023-11-30
2023-12-01..2023-12-31

PHP v5.6.40 requires you set the timezone or the default timezone like date_default_timezone_set('UTC'); before creating the DateTimes, but then you get the same output as above.

Run it live here.

CodePudding user response：

If your main goal is to output the start and end of each month within a given date range, inclusive of the end month, you can simplify this down to:

$from = new DateTime("2023-01-01");
$to   = new DateTime("2023-12-31");

while ($from <= $to) {
    echo $from->format("Y-m-01") . ".." . $from->format("Y-m-t") . "\n";
    $from->add(new DateInterval("P1M"));
}

If you need to respect the $to date, that is; if you need last date range to end at the $to date, you can adjust the above code slightly using the min() function:

$from = new DateTime("2023-01-01");
$to   = new DateTime("2023-12-31");

while ($from <= $to) {
    echo $from->format("Y-m-01") . ".." . min($to->format("Y-m-d"), $from->format("Y-m-t")) . "\n";
    $from->add(new DateInterval("P1M"));
}

CodePudding user response：

To use datetime objects in a loop like @ArleighHix's answer, I'd only modify the start date and use a calls of min() and max() in conjunction with 01 and t to ensure that date boundaries are not exceeded.

max() and min() are safe in this case because Y-m-d is a "big-endian" date format -- this means that the string can be evaluated as a simple string.

Code: (Demo)

$start_date = new DateTime("2023-01-03");
$end_date = new DateTime("2023-12-15");

while ($start_date <= $end_date) {
    printf(
        "%s..%s\n",
        max($start_date->format("Y-m-01"), $start_date->format("Y-m-d")),
        min($end_date->format("Y-m-d"), $start_date->format("Y-m-t"))
    );
    $start_date->modify(' 1 month first day of');
}

If your actual project requirement is to have non-full date ranges each month, then a refactored approach would be necessary. Please provide a more challenging example by editing your question if this is a real concern/possibility.