file reading C# .NET

Question

Hello,

I have a binary file. It consists of 4 messages, each is inthe size of 100 bytes. I want to read that last 2 messages again. I am using BinaryReader object. I seek to psosition 200 and then I read: BinaryReaderObject.read(charBuffer, 0, 10000), where charBuffer is big enougth. I get all the time the a mount of read is always missing 1. Instead of getting 200 I get 199. Instead of getting 400 I get 399. I checked and saw the size of the file is correct and the data that I get starts at the right place.

Thnaks,

Answer 1

Hint: zero-based array indexes, and zero-based positions ... First byte will start at position zero.

Answer 2

1. Seek to the end and print position. Is it as expected?
2. Print the position after reading the 199 -- is it as expected?
3. Try to read 1 more byte from the position after you get 199 -- do you get EOF?
4. How are you checking the size of the file?
5. Diff the 199 bytes with the expected ones -- what is different?

Two things I would check

1. CR/LF transformations
2. That the size is what you think it is.

Answer 3

Try this code and see what happens with your file.

 String message = @"Read {0} bytes into the buffer.";

 String fileName = @"TEST.DAT";

 Int32 recordSize = 100;

 Byte[] buffer = new Byte[recordSize];

 using (BinaryReader br = new BinaryReader(File.OpenRead(fileName)))
 {
    br.BaseStream.Seek(2 * recordSize, SeekOrigin.Begin);

    Console.WriteLine(message, br.Read(buffer, 0, recordSize));
    Console.WriteLine(message, br.Read(buffer, 0, recordSize));
 }

 Console.ReadLine();

I get the following output with a 400 byte test file.

Read 100 bytes into the buffer.
Read 100 bytes into the buffer.

If I seek to 2 * recordSize + 1 or use a 399 byte file, I get the following output.

Read 100 bytes into the buffer.
Read 99 bytes into the buffer.

So it works as expected.

Answer 4

The problem was that I used a wrapper to BinaryReader object. When calling the Read method there are some function overloding. Instead os using the signeture of char[], I used byte[]. Till now it worked fine because there was only use of utf-8, but now when I entered real binary data in the beginning of each message it caused the problem.