Convert serial value to date in perl - perl

Question

I am using Spreadsheet::XLSX to convert XLSX into CSV on Linux.
Custom date fields are being converted to numbers. I know that XLSX stores custom dates as serial values. I need to find the way to convert those values into dates/times.
Example:
CSV: 40829
XLSX: 10/13/2011 0:00
So I am trying to figure out how to convert 40829 to 10/13/2011 0:00
I did some research and I was not able to find any (Perl) solution.
I can provide the code if needed.
Please advise.
Thank you,
-Andrey

Answer 1

Excel stores dates and times as a number representing the number of days since 1900-Jan-0, plus a fractional portion of a 24 hour day: ddddd.tttttt.
You could write a function to do the calculations yourself or you could look at some of the modules already posted on cpan for doing this, DateTime::Format::Excel should do what you need and DateTimeX::Format::Excel looks like it would work too.

Answer 2

As per the previous post, this seems like it's the number of days since Jan 1st 1900. By making the 40828'th of January, 1900 (accounting for the off-by-one of being the 1st of January, not the 0th), we get:
use POSIX 'mktime'
my $epoch = mktime 0,0,0, 40829-1,0,0;
print scalar localtime($epoch);
Gives
Thu Oct 13 00:00:00 2011

Answer 3

Or you can use your own functions to convert the dates in EXCEL datevalue and back
sub date2excelvalue {
my($day1, $month, $year, $hour, $min, $sec) = #_;
my #cumul_d_in_m = (0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365);
my $doy = $cumul_d_in_m[$month - 1] + $day1;
#
full years + your day
for my $y(1900..$year) {
if ($y == $year) {
if ($month <= 2) {
#
dont add manually extra date
if inJanuary or February
last;
}
if ((($y % 4 == 0) && ($y % 100 != 0)) || ($y % 400 == 0) || ($y == 1900)) {
$doy++;#
leap year
}
} else {#
full years
$doy += 365;
if ((($y % 4 == 0) && ($y % 100 != 0)) || ($y % 400 == 0) || ($y == 1900)) {
$doy++;#
leap year
}
}
}#
end
for y# calculate second parts as a fraction of 86400 seconds
my $excel_decimaltimepart = 0;
my $total_seconds_from_time = ($hour * 60 * 60 + $min * 60 + $sec);
if ($total_seconds_from_time == 86400) {
$doy++;#
just add a day
} else {#
add decimal in excel
$excel_decimaltimepart = $total_seconds_from_time / (86400);
$excel_decimaltimepart = ~s / 0\. //;
}
return "$doy\.$excel_decimaltimepart";
}
sub excelvalue2date {
my($excelvalueintegerpart, $excelvaluedecimalpart) = #_;
my #cumul_d_in_m = (0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365);
my #cumul_d_in_m_leap = (0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366);
my #cumul_d_in_m_selected;
my($day1, $month, $year, $hour, $min, $sec);
$day1 = 0;#
all days all years
my $days_in_year;
my $acumdays_per_month;
my $daysinmonth;
my $day;
#
full years + your day
for my $y(1900. .3000) {
my $leap_year = 0;#
leap year
my $leap_year_mask = 0;#
leap year
if ((($y % 4 == 0) && ($y % 100 != 0)) || ($y % 400 == 0) || ($y == 1900)) {
$leap_year = 1;#
leap year
#cumul_d_in_m_selected = #cumul_d_in_m_leap;
} else {
$leap_year = 0;#
leap year
#cumul_d_in_m_selected = #cumul_d_in_m;
}
if (($day1 + (365 + $leap_year)) > $excelvalueintegerpart) {
#
found this year $y
$year = $y;
print "year $y\n";
$days_in_year = $excelvalueintegerpart - $day1;
$acumdays_per_month = 0;
print "excelvalueintegerpart $excelvalueintegerpart\n";
print "day1 $day1\n";
print "daysinyear $days_in_year\n";
for my $i(0..$# cumul_d_in_m) {
if ($i == $# cumul_d_in_m) {
$month = $i + 1;#
month 12 December
$day = $days_in_year - $cumul_d_in_m_selected[$i];
last;
} else {
if (($days_in_year > ($cumul_d_in_m_selected[$i])) && ($days_in_year <= ($cumul_d_in_m_selected[$i + 1]))) {
$month = $i + 1;
$day = $days_in_year - $cumul_d_in_m_selected[$i];
last;
}
}
}#
end
for $i months
# end year
last;
} else {#
full years
$day1 += (365 + $leap_year);
}
}#
end
for years interger part comparator
my $total_seconds_inaday;
$total_seconds_inaday = "0\.$excelvaluedecimalpart" * 86400;
$sec = $total_seconds_inaday;
$hour = int($sec / (60 * 60));
$sec -= $hour * (60 * 60);
$min = int($sec / 60);
$sec -= $min * (60);
$sec = int($sec);
return ($day, $month, $year, $hour, $min, $sec);
}
my $excelvariable = date2excelvalue(1, 3, 2018, 14, 14, 30);
print "Excel variable: $excelvariable\n";
my($integerpart, $decimalwithoutzero) = ($1, $2) if ($excelvariable = ~m / (\d + )\.(\d + ) / );
my($day1, $month, $year, $hour, $min, $sec) = excelvalue2date($integerpart, $decimalwithoutzero);
print "Excel Date from value: $day1, $month, $year, $hour, $min, $sec\n";
Enjoy it!