CSharp/C#, DateTime.ParseExact format issue

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CSharp/C# >> DateTime.ParseExact format issue

by John B » Mon, 01 Sep 2008 13:01:56 GMT

Hi all,
Any idea why this code results in a FormatException?

DateTime.ParseExact("40708", "dMMyy", CultureInfo.CurrentCulture)
If I use "040708" with the same format string it works and it parses all
double digit days fine.

TIA

JB

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CSharp/C# >> DateTime.ParseExact format issue

by Peter Duniho » Mon, 01 Sep 2008 13:26:08 GMT



I don't know for sure. But it doesn't surprise me that much that it
doesn't work. The degree of analysis that would be required for the
parser to successfully figure deal with variable-length parameters is
non-trivial. The parser is probably trying to parse "40" as a day value
and of course failing.

Your specific example is simpler, but if it's to work, then the parser
would be required to handle all of the variable-length fields as well.
Suppose your format was "dMyy". How does the parser know the difference
between a valid string "41208" (where the day is "4" and the month is
"12") and an invalid string "41208" (where the day is "41" and the month
is "2")? You can't allow the parser to be lenient, because then bad data
could wind up parsed successfully without any indication of an error.

I think the lesson is that if you want to use ParseExact(), your format
string needs to be unambiguous about each character position, which means
the variable-length fields like "d" and "M" are just not a good idea.

Pete
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CSharp/C# >> DateTime.ParseExact format issue

by John B » Mon, 01 Sep 2008 13:32:42 GMT


Thanks for your thoughts Peter, you're correct in a way.
The problem is though that it's data taken out of MS Excel and therefore
any leading zero is stripped.

Cheers,

JB
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CSharp/C# >> DateTime.ParseExact format issue

by Peter Duniho » Mon, 01 Sep 2008 13:40:31 GMT


The fact that the data comes from Excel doesn't change anything about what
I wrote. I'm not aware of any requirement that the .NET Framework provide
for built-in processing of data emitted by Excel.

You may well have to do some pre-processing of the data before parsing,
such as adding a leading '0' when the string length is less then 6.
Alternatively, depending on how much control you have over the Excel
worksheet that's providing the data, have Excel emit data that is better
suited to .NET's built-in parsing capabilities.

Pete
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CSharp/C# >> DateTime.ParseExact format issue

by John B » Mon, 01 Sep 2008 13:48:23 GMT


Thanks for your response.

JB
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CSharp/C# >> DateTime.ParseExact format issue

by QXJuZSBWYWpow7hq » Sun, 07 Sep 2008 08:15:40 GMT


It should be rather simple. Based on the description it is only
the first zero that disappears so replacing:

DateTime.ParseExact(s, "ddMMyy", CultureInfo.CurrentCulture)

with:

DateTime.ParseExact(s.PadLeft(6, '0'), "ddMMyy", CultureInfo.CurrentCulture)

should fix it.

Arne
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