To know what date format a user's machine is set to, you can use the 'CultureInfo' class and the 'DateTimeFormat' properties. You CAN NOT change a user's machine date time formats, you will not have many users left within the first day of your app -
MS Learn | CultureInfo Class[
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Quote:
The CultureInfo class provides culture-specific information, such as the language, sublanguage, country/region, calendar, and conventions associated with a particular culture. This class also provides access to culture-specific instances of the DateTimeFormatInfo, NumberFormatInfo, CompareInfo, and TextInfo objects.
To use this in code to determine the user's date format -
using System;
using System.Globalization;
CultureInfo userCulture = CultureInfo.CurrentCulture;
string dateFormat = userCulture.DateTimeFormat.ShortDatePattern;
Assuming you want to use the date in a string, you can use the 'DateTime' class to get the current date and then format it using the above determined 'dateFormat' -
using System;
using System.Globalization;
CultureInfo userCulture = CultureInfo.CurrentCulture;
string dateFormat = userCulture.DateTimeFormat.ShortDatePattern;
string myString = "This is the date: ";
DateTime currentDate = DateTime.Now;
string formattedDate = currentDate.ToString(dateFormat);
string resultString = myString + formattedDate;
Console.WriteLine(resultString);
No messing with a users settings or his machine...