When is it okay to check if a file exists?

Question

File systems are volatile. This means that you can\'t trust the result of one operation to still be valid for the next one, even if it\'s the next line of code. You can\'t

Answer 1

While this is a language-agnostic post, it seems you are talking about .NET. Most systems (.NET and others) have more detailed APIs in order to figure out if the file exists when opening the file.

What you should do is make a call to access the file, as it will typically indicate through some sort of error that the file doesn't exist (if it truly doesn't). In .NET, you would have to go through the P/Invoke layer and use the CreateFile API function. If that function returns an error of ERROR_FILE_NOT_FOUND, then you know that the file does not exist. If it returns successfully, then you have a handle that you can use.

The point here is that it is a somewhat atomic operation, which ultimately is what you are looking for.

Then, with the handle, you can pass it to a FileStream constructor and perform your work on the file.