How can I create a temp file with a specific extension with .NET?

c# .net temporary-files
Brann picture Brann · Feb 24, 2009 · Viewed 217.3k times · Source

I need to generate a unique temporary file with a .csv extension.

What I do right now is 

string filename = System.IO.Path.GetTempFileName().Replace(".tmp", ".csv");

However, this doesn't guarantee that my .csv file will be unique.

I know the chances I ever got a collision are very low (especially if you consider that I don't delete the .tmp files), but this code doesn't looks good to me.

Of course I could manually generate random file names until I eventually find a unique one (which shouldn't be a problem), but I'm curious to know if others have found a nice way to deal with this problem.

Answer

Mitch Wheat picture Mitch Wheat · Feb 24, 2009

Guaranteed to be (statistically) unique:

string fileName = System.IO.Path.GetTempPath() + Guid.NewGuid().ToString() + ".csv";

(To quote from the wiki article on the probabilty of a collision:

...one's annual risk of being hit by a meteorite is estimated to be one chance in 17 billion [19], that means the probability is about 0.00000000006 (6 × 10−11), equivalent to the odds of creating a few tens of trillions of UUIDs in a year and having one duplicate. In other words, only after generating 1 billion UUIDs every second for the next 100 years, the probability of creating just one duplicate would be about 50%. The probability of one duplicate would be about 50% if every person on earth owns 600 million UUIDs

EDIT: Please also see JaredPar's comments.

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