FileStream ReadWrite in C#

Question

I have a FileStream open as follows:

FileInfo file = new FileInfo(@"C:\Project.xml");
FileStream stream = file.Open(FileMode.Open, FileAccess.ReadWrite, FileShare.None);
XmlDocument document = new XmlDocument();
document.Load(stream);

The stream is opened when a project file is loaded. Now I need to be able to overwrite its contents when changes are saved. At this point, I have a reference to the FileStream object which is kept open to prevent other apps/users making changes to it.

What I don't understand is how the write method will work. The size of the previous and new data may be different. So the following code does not make sense.

stream.Position = 0;
document.Save(stream);
stream.Close();

How is it possible to overwrite the contents without closing the stream and reopening it? It seems illogical and if it is, how can I ensure that the file does not get locked by something else during the short time between closing and reopening the stream?

Answer 1

If the new document is longer than the old one, the file (and stream) will automatically expand.

If not, you can truncate the file by calling stream.SetLength() .
You would want to set it to stream.Position , which indicates how many bytes have been written so far.