Re: How to subtract date by 1 day

I tend to use a couple of routines I wrote. They take leap years into account, and expect the date to be passed in as YYYYMMDD

sub DateNext {
  my ($y, $m, $d) = unpack('a4a2a2', $_[0]);
  my @daysinmonth = ("31","28","31","30","31","30","31","31","30","31"
+,"30","31");
  my @daysinmonthly = ("31","29","31","30","31","30","31","31","30","3
+1","30","31");
  $d++;
  if (($y % 4) == 0) {
    if ($d > @daysinmonthly[$m - 1]) {
      $m++;
      if ($m > 12) {
        $m = 1;
        $y++;
      } ## End if
      $d = 1;
    } ## End if
  } ## End if
  else {
    if ($d > @daysinmonth[$m - 1]) {
      $m++;
      if ($m > 12) {
        $m = 1;
        $y++;
      } ## End if
      $d = 1;
    } ## End if
  } ## End else
  my $returndate = sprintf("%04d%02d%02d",$y,$m,$d);
  return $returndate;
} ## End sub

### Brings date to the previous day
sub DatePrevious {
  my ($y, $m, $d) = unpack('a4a2a2', $_[0]);
  my @daysinmonth = ("31","28","31","30","31","30","31","31","30","31"
+,"30","31");
  my @daysinmonthly = ("31","29","31","30","31","30","31","31","30","3
+1","30","31");
  $d--;
  if (($y % 4) == 0) {
    if ($d < 1) {
      $m--;
      if ($m < 1) {
        $m = 12;
        $y--;
      } ## End if
      $d = @daysinmonthly[$m - 1];
    } ## End if
  } ## End if
  else {
    if ($d < 1) {
      $m--;
      if ($m < 1) {
        $m = 12;
        $y--;
      } ## End if
      $d = @daysinmonth[$m - 1];
    } ## End if
  } ## End else
  my $returndate = sprintf("%04d%02d%02d",$y,$m,$d);
  return $returndate;
} ## End sub
[download]

Lyle

Comment on Re: How to subtract date by 1 day Download Code

Replies are listed 'Best First'.
Re^2: How to subtract date by 1 day by KurtSchwind (Chaplain) on Dec 13, 2007 at 16:14 UTC
Actually, there is a flaw in your Leap_year logic. (This is why people who write date routines pull out their hair). A leap year is a year that is divisible by 4, but not by 100, unless it's divisible by 400. Not that your solution is likely to encouter the bug anytime soon. But the year 2100 is NOT a ly. -- I used to drive a Heisenbergmobile, but every time I looked at the speedometer, I got lost.	[reply]
Re^2: How to subtract date by 1 day by Anonymous Monk on Apr 08, 2020 at 12:51 UTC
Leap year evaluation condition need to be updated- `(((($y%4) == 0) && (($y%100) !=0)) \|\| (($y%400) ==0) )`	[reply] [d/l]