Is there a way to compare date "strings" in C# without converting the strings?

Question

I have two fields:

string date1 = "04/26/10";
string date2 = "04/25/10";

How can I compare these two fields like so?:

if (date2 <= date1)
{
  // perform some code here
}

Can this be done without first converting the fields to a separate date-type variable?

EDIT: I should mention that these values are coming from a database table where the date values are in a string format to begin with. Old legacy code...

Answer 1

No, but it is not difficult to convert to a date in C#.

if ( DateTime.Parse(date2,CultureInfo.InvariantCulture) <=  DateTime.Parse(date1,CultureInfo.InvariantCulture))

{
  // perform some code here
}

CultureInfo depends on the format the string dates have in the legacy DB. See: DateTime formats used in InvariantCulture

Answer 2

If your dates are actually stored as strings in the database, it seems like you can't be sure they'll be in a valid format before parsing. For that reason I'd suggest a small variation on jle's answer:

DateTime d1, d2;
if (DateTime.TryParse(date1, out d1) &&
    DateTime.TryParse(date2, out d2) &&
    d2 <= d1)
{
    // perform some code here
}
else
{
    // strings didn't parse, but hey,
    //at least you didn't throw an exception!
}

Answer 3

At the very least you need to pick apart the strings in order to compare them in the right order.

If you want to leave them as strings, then you need to reorder them with LARGEST->SMALLEST units, so this:

yyyy/mm/dd

can be compared directly, but not the format you have. With your format, you need to split it, and either recombine it like above, or compare the individual pieces in the right order.

Having said that, it is rather easy to convert the strings to DateTime using DateTime.ParseExact.

Answer 4

Generally it is a bad idea to compare date as strings.

But if your strings are in the same format (e.g. yyyy/mm/dd means years, then monthes then days) then the comparison may be valid.

Answer 5

It could be done with string manipulation, but it would come down to effectively comparing three sets of integers, which as strings would induce more overhead than converting to datetimes. Why would you want to do that?

Answer 6

It's preferred to have the date formatted before doing the comparison. Depending in your cultureinfo, the safest way to compare dates is to format the date string to "yyyy-mm-dd".

DateTime d1, d2;
string date1 = "04/26/10";
string date2 = "04/25/10";
d1 = DateTime.Parse(date1.ToString("yyyy-MM-dd"));
d2 = DateTime.Parse(date2.ToString("yyyy-MM-dd"));
if (d1 > d2)
{
      //do something
}

Answer 7

No. Let the .net framework sort that out for you. It will correctly identify the user date settings and format (using system settings, current thread) and determine which is the month, year and day - especially if that data comes from eg a sql server.

Answer 8

Best practice is to avoid comparing date as string types and compare with the official DateTime object of C#.

If your use-case requires the comparison using string objects then:

• 1st, make sure the date string format is yyyymmdd as recommend by Lasse V. Karlsen.
• 2nd, use the string method CompareTo to compare between the dates.

Here's how the method works in your case (Used C# Online Compiler to test this):

using System;
public class Program
{
    public static void Main()
    {
        string fmt = "yyyymmdd";
        string min = "20201206";
        string max = "20210810";
        Console.WriteLine(max.CompareTo(min)); // Output :  1
        Console.WriteLine(min.CompareTo(max)); // Output : -1
        string same1 = "20001212";
        string same2 = "20001212";
        Console.WriteLine(same1.CompareTo(same2)); // Output : 0
        Console.WriteLine(same2.CompareTo(same1)); // Output : 0
        // Summary:
        // 1 = Greater than string param
        // -1 = lesser than string param
        // 0 = equals to string param
    }
}