StreamReader and Peek()

[Dan]

Hi, I'm having a problem with StreamReader.Peek(). Let's say I open a file
and read it to end; then I'd want to move its stream pointer back to the
file beginning: I can call BaseStream Seek method or change the value of the
Position property, but this does not seem to affect the Peek() method, which
keeps returning -1 as if it had not been notified that the stream pointer
has been repositioned to file beginning. How can I let Peek() work as
expected (i.e. return a value >=0 once the stream has been repositioned)?

Here's a sample code to reproduce my issue. Thx to all!

StreamReader sr = new StreamReader("c:\\work\\somefile.txt"))
Debug.Assert(sr.Peek()>-1); // OK
sr.ReadToEnd();
Debug.Assert(sr.Peek()==-1); // OK
sr.BaseStream.Seek(0L, SeekOrigin.Begin); // or
sr.BaseStream.Position = 0L;
Debug.Assert(sr.Peek()>-1); // ASSERTION FAILS!!!

[Jon Skeet [C# MVP]]

Dan <df***@hotmail.com> wrote:

Hi, I'm having a problem with StreamReader.Peek(). Let's say I open a file
and read it to end; then I'd want to move its stream pointer back to the
file beginning: I can call BaseStream Seek method or change the value of the
Position property, but this does not seem to affect the Peek() method, which
keeps returning -1 as if it had not been notified that the stream pointer
has been repositioned to file beginning. How can I let Peek() work as
expected (i.e. return a value >=0 once the stream has been repositioned)?

Use StreamReader.DiscardBufferedData. Basically, StreamReader often
reads more than you ask it to, keeping the read data in a buffer to
make things more efficient. DiscardBufferedData tells it that things
have changed, and it should ignore whatever it had already read.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
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