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DateTime.Parse/TryParse fails if the date and time uses the same separator #4409

GeirGrusom opened this issue Jul 31, 2015 · 5 comments


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@GeirGrusom GeirGrusom commented Jul 31, 2015

The following code (in .NET 4.6) throws a FormatException:

var dateFormat = new DateTimeFormatInfo
    DateSeparator = ".",
    TimeSeparator = ".",

var textDate = new DateTime(2015, 1, 1).ToString(dateFormat); // 01.01.2015 00.00.00
var reverse = DateTime.Parse(textDate, dateFormat); // Throws FormatException

Windows 10 for some reason changed the time separator for some locales (norwegian, finnish and serbian) which now breaks with Parse and TryParse.

edit: missed the format on the parse.

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@weshaggard weshaggard commented Jul 31, 2015

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@tarekgh tarekgh commented Jul 31, 2015

This is known issue and not a new one. the parser is just thinking it is parsing a time (and not a date) and then decide it is not valid time. in general the Parse/TryParse is not guaranteeing the parse all possible strings and we always recommend to use ParseExact/TryParseExact to guarantee successful parsing.
Fixing the parser will not be trivial as it is written as finite state machine. we'll try to look if there is a safe way can fix this without breaking other cases

@tarekgh tarekgh self-assigned this Aug 20, 2015
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@jouniheikniemi jouniheikniemi commented Aug 27, 2015

Regarding the same issue in .NET Framework, see my blog post at And now that the state machine has been fixed there, I hope the fix will flow down here as well :-)

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@tarekgh tarekgh commented Aug 30, 2015

The fix is already in the github side too. I didn't resolve this issue yet because I want to add some tests before closing the issue. let me know if you have any question.

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@tarekgh tarekgh commented Sep 22, 2015

The issue has been fixed and added the needed tests. closing the issue here.

@tarekgh tarekgh closed this Sep 22, 2015
@msftgits msftgits transferred this issue from dotnet/coreclr Jan 30, 2020
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