Im getting error Unable to read beyond the end of the stream why?

Question

The testing.res file is 240MB size. I want to read it. But im getting the error on this line:

int v = br.ReadInt32();

EndOfStreamException Unable to read beyond the end of the stream

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            R();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        public void R()
        {
            using (var br = new System.IO.BinaryReader(File.Open(@"d:\testing.res", FileMode.Open)))
            {
                // 2.
                // Position and length variables.
                int pos = 0;
                // 2A.
                // Use BaseStream.
                int length = (int)br.BaseStream.Length;
                while (br.BaseStream.Position < length)
                {
                    // 3.
                    // Read integer.
                    int v = br.ReadInt32();
                    textBox1.Text = v.ToString();
                }

            }
        }
    }
}

The exception:

System.IO.EndOfStreamException was unhandled
  Message=Unable to read beyond the end of the stream.
  Source=mscorlib
  StackTrace:
       at System.IO.BinaryReader.FillBuffer(Int32 numBytes)
       at System.IO.BinaryReader.ReadInt32()
       at WindowsFormsApplication1.Form1.R() in D:\C-Sharp\BinaryReader\WindowsFormsApplication1\WindowsFormsApplication1\Form1.cs:line 41
       at WindowsFormsApplication1.Form1..ctor() in D:\C-Sharp\BinaryReader\WindowsFormsApplication1\WindowsFormsApplication1\Form1.cs:line 19
       at WindowsFormsApplication1.Program.Main() in D:\C-Sharp\BinaryReader\WindowsFormsApplication1\WindowsFormsApplication1\Program.cs:line 18
       at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
       at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
       at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
       at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
       at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
       at System.Threading.ThreadHelper.ThreadStart()
  InnerException: 

Answer 1

You should use a more reliable way of figuring out when you are at the end of the stream, rather than rolling your own counter with sizeof(int) . Your method may not be precise enough, and the fact that you are using an unsafe code for that is also not too good.

One way probe if you are at the end of the stream or not is to use the PeekChar method:

while (br.PeekChar() != -1)
{
    // 3.
    // Read integer.
    int v = br.ReadInt32();
    textBox1.Text = v.ToString();
}

A more common solution is to write the number of int s that you are saving in a binary file in front of the actual list of integers. This way you know when to stop without relying on the length or the position of the stream.

Answer 2

One reason your code could fail is if file contains extra bytes (ie 7 byte long file). Your code will trip on last 3 bytes.

To fix - consider computing number of integers in advance and using for to read:

var count = br.BaseStream.Length / sizeof(int);
for (var i = 0; i < count; i++)
{
  int v = br.ReadInt32();
  textBox1.Text = v.ToString();
}

Note that this code will simply ignore last 1-3 bytes if they are there.

Answer 3

The binary reader is not pointing to the start of the stream.

Use this code before reading the integer value:

br.BaseStream.Seek(0, SeekOrigin.Begin);