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How to make a valid Windows filename from an arbitrary string?

Asked 2009-03-06T22:05:17.493
117

I've got a string like "Foo: Bar" that I want to use as a filename, but on Windows the ":" char isn't allowed in a filename.

Is there a method that will turn "Foo: Bar" into something like "Foo- Bar"?

c# windows filenames
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2 Answers

39
fileName = fileName.Replace(":", "-")

However ":" is not the only illegal character for Windows. You will also have to handle:

/, \, :, *, ?, ", <, > and |

These are contained in System.IO.Path.GetInvalidFileNameChars();

Also (on Windows), "." cannot be the only character in the filename (both ".", "..", "...", and so on are invalid). Be careful when naming files with ".", for example:

echo "test" > .test.

Will generate a file named ".test"

Lastly, if you really want to do things correctly, there are some special file names you need to look out for. On Windows you can't create files named: 

CON, PRN, AUX, CLOCK$, NUL
COM0, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9
LPT0, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9.
answered 2009-03-06T22:14:28.953
8

Diego does have the correct solution but there is one very small mistake in there. The version of string.Replace being used should be string.Replace(char, char), there isn't a string.Replace(char, string)

I can't edit the answer or I would have just made the minor change.

So it should be:

string fileName = "something";
foreach (char c in System.IO.Path.GetInvalidFileNameChars())
{
   fileName = fileName.Replace(c, '_');
}
answered 2009-09-09T07:49:16.607

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