I want to check if a given string is a valid .net date format.
so i have the following function that checks if the date format is correct
public void IsValidDateFormat(string dateFormat)
{
var flag = true;
try
{
DateTime.ParseExact(DateTime.Now.ToString(),
dateFormat,
System.Globalization.CultureInfo.InvariantCulture);
}
catch (Exception ex)
{
flag = false;
}
return flag;
}
However, The method is not working as expected. For a valid date format also it returns false.
dateFormat = ,, => returns false =>Passed
dateFormat = someinvalidformat => returns false =>Passed
dateFormat = MM/dd/yyyy => returns false => Not Passed
So MM/dd/yyyy is valid dateformat. But method returns false.
Is there a better way to check if given date format is valid .Net date format?
Update 1
I understand why method fails for MM/dd/yyyy or for other valid date formats. I am not asking why it fails. MM/dd/yyyy is just common valid date time format i am using here for example.
I am looking for a way to check if the given date format is valid .Net date format. So it could be any .Net date format.
Since the format returned by DateTime.ToString does not match your format (it includes the time part), ParseExact fails.
Validate the format by using public string ToString(string format, System.IFormatProvider provider) instead
public bool IsValidDateFormat(string dateFormat)
{
try {
string s = DateTime.Now.ToString(dateFormat, CultureInfo.InvariantCulture);
DateTime.Parse(s, CultureInfo.InvariantCulture);
return true;
} catch {
return false;
}
}
Note that date/time formats that may seem not to be valid, can in fact be valid, as some non-format characters are just outputted as is. E.g.
DateTime.Now.ToString("abcdefg", CultureInfo.InvariantCulture)
results in "abc27e6A.D.". So it is in fact a valid date/time format, even if it does not make a lot of sense. You can enhance the quality of the test by trying to parse the resulting date string. This will eliminate a lot of nonsensical formats.
This test ...
Console.WriteLine(IsValidDateFormat(",,"));
Console.WriteLine(IsValidDateFormat("a"));
Console.WriteLine(IsValidDateFormat("MM/dd/yyyy hh:mm:ss"));
Console.WriteLine(IsValidDateFormat("MM/dd/yyyy"));
Console.WriteLine(IsValidDateFormat("abcdefg"));
Console.ReadKey();
... prints
False
False
True
True
False
why not TryParse() or exact version? https://learn.microsoft.com/es-es/dotnet/api/system.datetime.tryparse?view=netframework-4.8
returns true if system can parse.
It does "the same" your method does.
Related
Seeing a strange issue where on some systems the below code steps into the if statement (i.e. it returns true) while in other systems it returns false and steps into the else statement. What environmental conditions or framework version changes am I missing where this was changed? For example .net Fiddle returns true, but my own console apps return false.
DateTime time;
formatText = "";
if (DateTime.TryParse (DateTime.Now.ToString(formatText), CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out time))
{
// If TryParseExact Worked
Console.WriteLine ("True: " + time.ToString ());
}
else
{
// If TryParseExact Failed
Console.WriteLine ("Failed to Parse Date");
}
String representations of DateTime are culture specific.
Passing an empty string or null as the format parameter of the ToString overload of DateTime is the same as passing the standard format specifier "G" - from the remarks section of the DateTime.ToString Method (String) msdn page:
If format is null or an empty string, the general format specifier, 'G', is used.
The TryParse overload you are using attempts to parse the DateTime value using the date and time formats available in the IFormatProvider format parameter - InvariantCulture in your case - so when you use TryParse with InvariantCulture, unless your current culture's ShortDatePattern and LongTimePattern properties are the same as in InvariantCulture, the tryParse will fail.
I have the following method in order to verify whether a string is a valid datetime:
public bool isDate(string date)
{
bool check = false;
try
{
DateTime converted_date = Convert.ToDateTime(date);
check = true;
}
catch (Exception)
{
check = false;
}
return check;
}
Now, the exception "String was not recognized as valid datetime" is caught whenever I try to pass a string like this:
"12/31/2013 12:00:00 AM"
I cannot understand why this is happening. Can someone help me solve this please?
Instead of the try/catch block, try the built in TryParse method in the DateTime class. It takes your string as a parameter and if it converts successfully it will place the value in the "result" variable. It returns a boolean value representing whether it worked or not.
public bool isDate(string date)
{
var result = new DateTime();
return DateTime.TryParse(date, out result);
}
Most likely your current culture settings are different from the format date is provided in. You can try specifying the culture explicitly:
CultureInfo culture = new CultureInfo("en-US"); // or whatever culture you want
Convert.ToDateTime(date, culture);
You can also use DateTime.TryParseExact and pass a format string (eg. MM/dd/yy H:mm:ss zzz, see more here) to check if the date has a specific format.
I am suppose to let the user enter a DateTime format, but I need to validate it to check if it is acceptable. The user might enter "yyyy-MM-dd" and it would be fine, but they can also enter "MM/yyyyMM/ddd" or any other combination. Is there a way to validate this?
Are you looking for something like this?
DateTime expectedDate;
if (!DateTime.TryParse("07/27/2012", out expectedDate))
{
Console.Write("Luke I am not your datetime.... NOOO!!!!!!!!!!!!!!");
}
If your user knows the exact format(s) needed...
string[] formats = { "MM/dd/yyyy", "M/d/yyyy", "M/dd/yyyy", "MM/d/yyyy" };
DateTime expectedDate;
if (!DateTime.TryParseExact("07/27/2012", formats, new CultureInfo("en-US"),
DateTimeStyles.None, out expectedDate))
{
Console.Write("Thank you Mario, but the DateTime is in another format.");
}
I don't know of any way to actually validate the format they enter since sometimes you want to intentionally include characters that translate into anything. One thing you might consider is allowing the user to self validate by showing a preview of what their entered format translates into.
I assume you want to know if the specified format string is valid...
For this you could round-trip it:
private bool IsValidDateFormat(string dateFormat)
{
try
{
String dts=DateTime.Now.ToString(dateFormat, CultureInfo.InvariantCulture);
DateTime.ParseExact(dts, dateFormat, CultureInfo.InvariantCulture);
return true;
}
catch (Exception)
{
return false;
}
}
Unless I am remembering incorrectly, the only invalid DateTime format strings are one character long. You can assume any 2 or more character DateTime format string is valid.
DateTime.ParseExact("qq", "qq", null) == DateTime.Today
DateTime.ParseExact("myy", "501", null) == "05/01/2001"
Standard (1 character)
Custom (>1 character)
For reference, allowed single character strings as formats:
d,D,f,F,g,G,m,M,o,O,r,R,s,T,u,U,y,Y
Any other character, such as q, by itself is invalid. All other strings will be successfully parsed as formatting strings.
You don't talk about your validation strategy. Anyway you should use something involving regular expressions and than apply allowed patterns. This would help against the formal validity .. then you have to take care about the actual contents and be sure the values are correct according as month, day and year.
Anyway several people suggested to use the DateTime.TryParse() method to let the substrate take care for you. But you'll have to specify the format anyway! so there's no magic! you would fall in ambiguity otherwise
This works for me-
try
{
String formattedDate = DateTime.Now.ToString(dateFormat);
DateTime.Parse(formattedDate);
return true;
}
catch (Exception)
{
return false;
}
static private bool IsValidDateFormat(string dateFormat)
{
try
{
DateTime pastDate = DateTime.Now.Date.Subtract(new TimeSpan(10, 0, 0, 0, 0));
string pastDateString = pastDate.ToString(dateFormat, CultureInfo.InvariantCulture);
DateTime parsedDate = DateTime.ParseExact(pastDateString, dateFormat, CultureInfo.InvariantCulture);
if (parsedDate.Date.CompareTo(pastDate.Date) ==0)
{
return true;
}
return false;
}
catch
{
return false;
}
}
I do use this code - it is a modification of shapiro yaacov posting.
It looks as "DateTime.ParseExact" does not throw an exception when using an invalid dateformat string - it just returns "DateTime.Now".
My approach is to convert a date in the past to string and then check if this is returned by ParseExact()
The answer by ZipXap accepts any format that doesn't throw an exception, yet something like "aaaa" will pass that validation and give the current date at midnight ("26-Apr-22 00:00:00" when writing this).
A better aproach is to use the DateTimeStyles.NoCurrentDateDefault option and compare the result to default:
using System.Globalization;
var format = "aaaaa";
try {
var dt = DateTime.ParseExact(
DateTime.Now.ToString(format, CultureInfo.InvariantCulture),
format,
CultureInfo.InvariantCulture,
DateTimeStyles.NoCurrentDateDefault);
return dt != default;
} catch {
return false;
}
/*
"aaaaa" -> false
"h" -> false
"hh" -> true
"fff" -> true
"gg" -> false
"yyyy gg" -> true
"'timezone: 'K" -> false
"zzz" -> false
*/
My solution was to mark the input-field as read-only and allow users to change the value only by jqueryui datepicker.
It is intuitive. You can specify your preferred format and need only to validate this one format.
Otherwise you may get really in trouble. What are you going to do with "02/03/2020" in USA you interpret it as the third of February, but for south america it is definitely the second of March. And there are a lot of other Date formats around the globe.
I am using Datetime.TryParse method to check the valid datetime. the input date string would be any string data. but is returning false as the specify date in invalid.
DateTime fromDateValue;
if (DateTime.TryParse("15/07/2012", out fromDateValue))
{
//do for valid date
}
else
{
//do for in-valid date
}
Edit: I missed. I need to check the valid date with time as "15/07/2012 12:00:00".
Any suggestions are welcome.
You could use the TryParseExact method which allows you to pass a collection of possible formats that you want to support. The TryParse method is culture dependent so be very careful if you decide to use it.
So for example:
DateTime fromDateValue;
string s = "15/07/2012";
var formats = new[] { "dd/MM/yyyy", "yyyy-MM-dd" };
if (DateTime.TryParseExact(s, formats, CultureInfo.InvariantCulture, DateTimeStyles.None, out fromDateValue))
{
// do for valid date
}
else
{
// do for invalid date
}
You should be using TryParseExact as you seem to have the format fixed in your case.
Something like can also work for you
DateTime.ParseExact([yourdatehere],
new[] { "dd/MM/yyyy", "dd/M/yyyy" },
CultureInfo.InvariantCulture,
DateTimeStyles.None);
As the others said, you can use TryParseExact.
For more informations and the use with the time, you can check the MSDN Documentation
I want to convert text to datetime but having error.My text box value is in format dd/MM/yyyy
String was not recognized as a valid DateTime.
myFtMaster.GENTRTYDATEFROM =Convert.ToDateTime(txtTreatyPeriodfrom.Text.ToString());
My business object 'gentrtydatefrom' datatype is DateTime. Also what is the best way to avoid these type of errors without using a Try catch block.
You either specify a culture that uses that specific format:
myFtMaster.GENTRTYDATEFROM = Convert.ToDateTime(
txtTreatyPeriodfrom.Text, CultureInfo.GetCulture("en-GB")
);
or use the ParseExact method:
myFtMaster.GENTRTYDATEFROM = DateTime.ParseExact(
txtTreatyPeriodfrom.Text, "dd/MM/yyyy", CultureInfo.Invariant
);
The ParseExact method only accepts that specific format, while the Convert.ToDateTime method still allows some variations on the format, and also accepts some other date formats.
To catch illegal input, you can use the TryParseExact method:
DateTime d;
if (DateTime.TryParseExact(txtTreatyPeriodfrom.Text, "dd/MM/yyyy", CultureInfo.Invariant, DateTimeStyles.None, out d)) {
myFtMaster.GENTRTYDATEFROM = d;
} else {
// communcate the failure to the user
}
Use something like the following instead:
DateTime date = DateTime.MinValue;
DateTime.TryParse(txtTreatyPeriodfrom.Text, out date);
TryParse is similar to DateTime.Parse() but it does not throw an exception if the conversion fails.
If you want to use the en-CA specific culture use the following:
DateTime.TryParse(txtTreatyPeriodfrom.Text, new CultureInfo("en-CA"),
DateTimeStyles.AllowWhiteSpaces, out date);
Then obviously deal with those dates that fail to parse.
Ensuring the user is prompted on the format will obviously reduce mistakes.
Have a look at
DateTime.TryParse(String value, out DateTime, [culture settings])