Convert DateTime.Now to a valid Windows filename

Question

I have had this issue quite a few times and have just been using a workaround but thought I would ask here in case there is an easier option. When I have a string from DateTime.Now and I then want to use this in a filename I can't because Windows doesn't allow the characters / and : in filenames, I have to go and replace them like this:

string filename = DateTime.Now.ToString().Replace('/', '_').Replace(':', '_');

Which seems a bit of a hassle, is there an easier way to do this? Any suggestions much appreciated.

Solution 1

 DateTime.Now.ToString("dd_MM_yyyy")

Solution 2

As written by Samich, but

// The following will produce 2011-10-24-13-10
DateTime.Now.ToString("yyyy-MM-dd-HH-mm", CultureInfo.InvariantCulture);

If you don't trust me, try setting the culture to new CultureInfo("ar-sa"); :-)

I'll add that, if you hate the world, this is the most precise thing to do:

DateTime.Now.Ticks.ToString("D19");

There are 19 digits in DateTime.MaxValue.Ticks

If you hate the world even more:

DateTime.Now.Ticks.ToString("X16");

There are 16 hex digits in DateTime.MaxValue.Ticks.

Solution 3

Use a ToString pattern:

DateTime.Now.ToString("yyyy-MM-dd-HH-mm") // will produce 2011-10-24-13-10

Solution 4

If you need the datetime to be more precise you can use:

DateTime.Now.ToString("O").Replace(":", "_") //2016-09-21T13_14_01.3624587+02_00

or (if you need a little less)

DateTime.Now.ToString("s").Replace(":", "_") //2016-09-21T13_16_11

Both are valid file names and are sortable.

You can create an extensions method:

public static string ToFileName(this DateTime @this)
{
    return @this.ToString("O").Replace(":", "_");
}

And then use it like this:

var saveZipToFile = "output_" + DateTime.Now.ToFileName() + ".zip";

The "s" format does not take time zones into account and thus the datetimes:

• 2014-11-15T18:32:17+00:00
• 2014-11-15T18:32:17+08:00

formatted using "s" are identical.

So if your datetimes represent dirrerent time zones I would recommend using "O" or using DateTime.UtcNow.

• The "O" format is compliant with ISO 8601, described here
• The "s" format is described here

Solution 5

You can use timestamp's long format:

DateTime.Now.ToBinary()

View more solutions

Comments

[tenfour]

Can you use a more logical iso8601-style pattern like yyyyMMdd?

[Bali C]

Wow, I didn't know there was this much detail to DateTime, +1, thanks!

[xanatos]

@BaliC I'll add that if you are in the "sport" of using DateTime to number your files, you should probably use DateTime.UtcNow so that you don't have problems around DST change time.

[Royi Namir]

be aware from the capital MM which is month and not mm which is minute .. very important !

[Raymond Chen]

This assumes the language does not use illegal filename characters in its dd, MM, or yyyy format. True for English. Not necessarily true for other languages.

[xanatos]

You'll have to use HH instead of hh or instead of 14 you'll get 02

[Bali C]

@RoyiNamir Thanks, I have just tried using it and ran into that problem so came back to look at your answer, thanks!