SSRS 2008 date formatting and exporting to excel confusion

Question

Suppose I have a field with a date value in a Reporting Services template, e.g. =CDate("2010.12.03"), I apply the "d" format to this cell, which, according to the description, "will reflect the regional settings of the report". I generate the report using the English language, the date is displayed as 12/03/2010, which is fine. Now when I export this report to excel, I have no idea what the __ happens.

First scenario: the regional settings of the computer are set to English (United States). When I open the excel document, the value seen in the cell is 12/03/2010, as expected. When I click on it, I can see that the actual value stored in the cell is 2010.12.03, which also seems reasonable - some formatting is applied to the cell, it's not simply exported as text. But when I try to figure out what type of formatting is applied, by right clicking and checking Format Cells, I see that the format is "General", i.e. none! How can this be ? This is Excel 2010 by the way, but the file itself is .xls, of course.

Second scenario, where it gets more interesting: now the region of the computer is set to e.g. Lithuania, where the date format is 2010.12.03. I open the same document and see 12.03.2010. Now that simply does not make any sense. Exporting many times I've encountered that sometimes the cell is formatted as [$-10409]m.d.yyyy in excel (under the Custom section). What is this, what does the 10409 mean ? The weirdest part of all: if I close the document without saving, change the computer region back to English (United States), reopen the document, the format is now [$-10409]m/d/yyyy ! HOW is this possible !??

Basically the same thing happens with numbers and with thousand/decimal separators - excel uses the region of the computer to format these, but the actual format of the cell can be something like [$-10409]#,##0.00;-#,##0.00 or General - again, depending on the region of the computer, direction of wind and the temperature outside.

My question is then, first of all, what the __ is going on ? Second, how should the excel document behave according to the specs, i.e. what does the statement that a format "will reflect the regional settings of the report" in the BIDS designed, where I chose the "d" format for the date textbox, mean ? Does it mean, that the format will be determined by the language of the report and the result will look the same on all computers in the world (which makes sense, since this is how other formats behave, i.e. if you export the date to a pdf, it stays the same always) ? If not, which appears to be partially the case in excel, why doesn't the exported date cell have the regional date format, i.e. the one that you normally use in excel, the one which formats the date according to the region of the computer ?

Are these some kind of limitations of excel or what ? Why can't we have consistent behavior, i.e. either make everything sensitive to the culture of the computer viewing the document or don't, why is the actual behavior somewhere in between ?

Answer 1

Excel uses a custom encoding for the date, and uses the machine regional settings as a hint on how to format the contents. The encoding is archaic, and has lots of specific, historic gotchas.

This means that the kinds of bugs that you see often do happen - you'll have data that's been exported to Excel, which then has its formatting and contents mangled once opened for the first time by the actual Excel application. The problem can be anywhere along the line - maybe the library that exports the data to Excel doesn't deal with some of the more esoteric historic cases well, or maybe Excel is confusing itself along the way.

I've had some success in the past with exporting dates as a strings to a CSV file, stripped of formatting, and then importing them into Excel/opening them with Excel.