Custom date format in PHPExcel - php

Question

In my excel file I am building from PHP the first row is the header one. I need to put there several dates as column header. Each date is (in dd/mm/yyyy format) 15/mm/yyyy starting from 15/01/2007 and ending with 15/12/2018 stepping month by month.
My code is this:
for($anno = $annoMin; $anno<=$annoMax; $anno++){
for($mese = 1; $mese <= 12; $mese++){
$mese = sprintf("%02s", $mese);
$periodo = '15/'.$mese.'/'.$anno;
$periodo = strtotime($periodo);
$periodo = PHPExcel_Shared_Date::PHPToExcel($periodo);
array_push($header_array,$periodo);
}
}
I build the date as a string, convert it into a unix timestap, convert it into an excel date and push it into the $header_array.
Then I draw the cells in the excel:
$ews->fromArray($header_array, ' ', 'A1');
Finally I format the cells where there is a date as:
$ews->getStyle('U1:EJ1')
->getNumberFormat()
->setFormatCode(PHPExcel_Style_NumberFormat::FORMAT_DATE_DDMMYYYY);
ISSUES ARE:
Actually my code is returning 'False' for each cell with a date;
I need to add a custom mask that is not listed in the PHPExcel library: MM/YYYY to be shown in each cell.
For the first issue: I have checked different SO questions and followed mainly this one. with no luck.

Answer 1

Problem is here:
$periodo = '15/'.$mese.'/'.$anno;
$periodo = strtotime($periodo);
which would give a string values of 15/1/2015, 15/2/2015... ``15/12/2015that you're then attempting to convert to a unix timestamp usingstrtotime()`.
If you read the PHP Docs on date formats used by the strtotime() function, you'll see that a / separator tells PHP that the date string is US date format.... i.e. mm/dd/yyyygiving a month value of15` in every case, and (of course) there is no month 15
Either use a dash (-) rather than a / to indicate European (dd-mm-yyyy) rather than US date format
$periodo = '15-'.$mese.'-'.$anno;
$periodo = strtotime($periodo);
or re-order the values to use US format
$periodo = $mese.'/'.'15/'.$anno;
$periodo = strtotime($periodo);
And for the second part of your question.... you can supply almost any format mask that MS Excel recognises, you're not restricted to the built-in formats; so:
$ews->getStyle('U1:EJ1')
->getNumberFormat()
->setFormatCode('mm/yyyy');
The format code is simply a string value