What should I do to parse a string which is in fact a date format data ?

[lofonder]

<c r="B2" s="133">
<v>45905</v>
</c>

the code up what I just marked as the bold part.
the qxlsx parsed the part as a number.but it is a date data in fact.
and when I opened the xlsx files in the excel .the bold part was parsed as the date data too.
I did find nothing more about the cell(the bold part) .
I just wondered what the excel done to parse the part correctly and the qxlsx dint parsed the date part.