C# Parse DateTime using DateTime.TryParseExact() multiple format

Question

I have a string text that i want to parse/convert to DateTime,
the text can have a different formats (depending on the user who write it),
it can be "dd/MM/yyyy" or it can be "MM/dd/yyyy".

I am using DateTime.TryParseExact(string, formats[], provider, dateTimeStyles, out result)
as descripted here TryParseExact

Now the problem happens in the following cases
if (for example) string text = "06/01/2023"

The text could have two meanings
1^st --> Day: 06, Month: 01, Year: 2023
2^nd --> Day: 01, Month: 06, Year: 2023

My Question is when does the Method TryParseExact() return true
does it return true for the first format that matches text ?
or does it evalute all/each format inside the formats[] array ?

i have tried to search for a similar question, but i didn't seem to find one,
i have tried read this reference TryParseExactMultiple
i have tried this question

Thank you for your help in advance.

My code:

string text = "06/01/2023";

string[] formatsArray = new string[]
{
  "yyyyMMdd",
  "dd/MM/yyyy",
  "dd-MMM-yy",
  "MM/dd/yyyy",
  "MM-dd-yyyy"
};

DateTime result;

DateTime.TryParseExact(text, formatsArray, System.Globalization.CultureInfo.InvariantCulture, System.Globalization.DateTimeStyles.None, out result)

Output is:
result = Day: 06, Month: 01, Year: 2023

Looks like it tries them in the order you present them. If you swap the order in formatsArray, what answer does it give? — codeulike
– codeulike, Commented Dec 15, 2022 at 12:17
It doesn't matter how TryParseExact works because there's no way for humans to say what the correct date is. This is why people should not use localized formats. Where does this string come from? A UI element? HTTP request? CSV file? Whatever creates the string should either be modified to use DateTime instead, or it should use the ISO8601 format. — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Dec 15, 2022 at 12:24
@codeulike if I swap the order then result = Day: 01, Month: 06, Year: 2023 but still, how do I know which format is used in the parsing? — Bola Adel Nassif
– Bola Adel Nassif, Commented Dec 15, 2022 at 12:25
@BolaAdelNassif it doesn't matter which one is used - even you can't guess what that date is without additional information. If you know what locale was used, instead of TryParseExact it's better to use TryParse with the correct locale. — Panagiotis Kanavos
– Panagiotis Kanavos, Commented Dec 15, 2022 at 12:26

Guru Stron · Accepted Answer · 2022-12-15 12:42:20Z

3

It seems that source code is pretty clear - TryParseExact calls TryParseExactMultiple which cycles formats in provided order and returns first one that succeeds:

internal static bool TryParseExactMultiple(ReadOnlySpan<char> s, string?[]? formats,
    DateTimeFormatInfo dtfi, DateTimeStyles style, scoped ref DateTimeResult result)
{
    // ...

    // Do a loop through the provided formats and see if we can parse successfully in
    // one of the formats.
    for (int i = 0; i < formats.Length; i++)
    {
        string? format = formats[i];
        // ...
        if (TryParseExact(s, format, dtfi, style, ref innerResult))
        {
            result.parsedDate = innerResult.parsedDate;
            result.timeZoneOffset = innerResult.timeZoneOffset;
            return true;
        }
    }

    result.SetBadDateTimeFailure();
    return false;
}

Since documentation does not specify behaviour for I would not recommend to rely on it, if it is possible, or possibly wrap this into helper method which will be tested for your particular requirements.

In general - when accepting data from somewhere you need to agree on data format, if the source of the data is not under your control - contact the vendor to clarify it otherwise sooner or later the situation like this are bound to happen (in theory not only related to dates).

edited Dec 15, 2022 at 12:42

answered Dec 15, 2022 at 12:25

Guru Stron

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2 Comments

Panagiotis Kanavos Over a year ago

That doesn't answer the only question that matters - how to correctly parse such strings? The answer is good, the question is wrong.

Bola Adel Nassif Over a year ago

wrap this into helper method Thank you for your answer.

Crispy Holiday · Accepted Answer · 2022-12-15 12:19:01Z

0

According to the documentation, TryParseExact does not provide an indication for which format was used. My general recommendation is to allow users to send only one date format.

answered Dec 15, 2022 at 12:19

Crispy Holiday

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3 Comments

Bola Adel Nassif Over a year ago

Thank you for your help, what if I take inputs from two different sources and each source has his own format and I don't know the format of each source?

Guru Stron Over a year ago

@BolaAdelNassif you need to determine format for each of the sources and use different code to parse both.

Crispy Holiday Over a year ago

@BolaAdelNassif I don't know your specific use case, but I could suggest either having different endpoints depending on the request source (if this is an API) or writing a function that tries several formats one by one and returns the successful format. Why do you need to know the format?

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