C# - Stream/FileStream EOF

Question

Is anyone familiar with a way to find out you're at the end of the file? I'm using BinaryReader and tried PeekChar - but it throws an exception. Any other suggestions?

Thanks.

Do you want this to work for files only (which are seekable, I think), or for streams in general? — R. Martinho Fernandes, Feb 16 '11 at 12:30
The output char buffer is too small to contain the decoded characters, encoding 'Unicode (UTF-8)' fallback 'System.Text.DecoderReplacementFallback'. Parameter name: chars — eve, Feb 16 '11 at 12:51

score 11 · Answer 1 · answered Feb 16 '11 at 12:30

11

From a Stream, if you Read(buffer, offset, count) you'll get a non-positive result, and if you Peek() you'll get a negative result.

With a BinaryReader, the documentation suggests that PeekChar() should return negative:

Return Value

Type: System.Int32 The next available character, or -1 if no more characters are available or the stream does not support seeking.

are you sure this isn't a corrupt stream? i.e. the remaining data cannot form a complete char from the given encoding?

answered Feb 16 '11 at 12:30

Marc Gravell

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I've done while (binReader.PeekChar() ! = -1 ) {...} This is what I get: The output char buffer is too small to contain the decoded characters, encoding 'Unicode (UTF-8)' fallback 'System.Text.DecoderReplacementFallback'. Parameter name: chars – eve Feb 16 '11 at 12:46
@MarcGravell There is probably a bug/feature somewhere in the `DecoderReplacementFallback` so that `new BinaryReader(new MemoryStream(new byte[] { 194, 0, 0 })).PeekChar()` will throw an exception (not all the illegal sequences of three bytes will throw... For example `{ 192, 0, 0 }` won't – xanatos Apr 04 '17 at 12:38

score 2 · Answer 2 · answered Feb 16 '11 at 12:31

If your stream supports seeking (check this using the BaseStream.CanSeek property), check the Position property of the BaseStream, like so:

if (myBinaryReader.BaseStream.CanSeek){
   bool atEnd = (myBinaryReader.BaseStream.Position == myBinaryReader.BaseStream.Length - 1)
}

score 1 · Answer 3 · answered Aug 10 '17 at 16:20

1

Checking whether the position of the reader is less than its length does the trick

While BinReader.Position < BinReader.Length
{
 ... BinReader.Read() ...
}

answered Aug 10 '17 at 16:20

Nepaluz

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Using `Stream.Position` or `Stream.Length` will cause an exception if `CanSeek == false`. – Dai Oct 21 '20 at 08:57

score 0 · Answer 4 · answered Apr 04 '17 at 12:43

I'll add my suggestion: if you don't need the "encoding" part of the BinaryReader (so you don't use the various ReadChar/ReadChars/ReadString) then you can use an encoder that won't ever throw and that is always one-byte-per-char. Encoding.GetEncoding("iso-8859-1") is perfect for this. The iso-8859-1 encoding is a one-byte-per-character encoding that maps 1:1 all the first 256 characters of Unicode (so the byte 254 is the char 254 for example)

score -2 · Answer 5 · answered Feb 16 '11 at 12:30

-2

While BinReader.PeekChar() > 0
{
...
}

answered Feb 16 '11 at 12:30

Jaime Oro

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C# - Stream/FileStream EOF

5 Answers5

Return Value

Linked