Question

FileStream.Read() is defined as:

public override int Read(
    byte[] array,
    int offset,
    int count
)

How can I read some bytes from an offset bigger than int.MaxValue?

Let’s say I have a very big file and I want to read 100MB starting from position 3147483648.

How can I do that?

Answer 1

The offset here is the offset in the array at which to start writing. In your case, just set:

stream.Position = 3147483648;

and then use Read(). The offset is most commonly used when you know you need to read [n] bytes:

int toRead = 20, bytesRead;
while(toRead > 0 && (bytesRead = stream.Read(buffer, offset, toRead)) > 0)
{
    toRead -= bytesRead;
    offset += bytesRead;
}
if(toRead > 0) throw new EndOfStreamException();

this will read exactly 20 bytes into buffer (or throw an exception). Note that Read() is not guaranteed to read all the required data in one go, hence a loop incrementing an offset is usually required.