Question

How to read a part of binary file from byte N1 to byte N2 in C#

Answer 1

using System;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                Console.WriteLine("\nread the first 13 bytes\n");
                ReadBinaryFile("d:\\image.gif", 0, 13);
                Console.WriteLine("\n\nread the last 10 bytes\n");
                ReadBinaryFile("d:\\image.gif", -10, 10);
                Console.WriteLine("\n\nread from byte 30 5 bytes \n");
                ReadBinaryFile("d:\\image.gif", 30, 5);
                Console.WriteLine("\n\nread from byte 15 30000 bytes\n");
                ReadBinaryFile("d:\\image.gif", 15, 3000); // will show nothing, file size is < 30000
            }
            catch (IOException ioex)
            {
                Console.WriteLine(ioex.Message);
            }
        }
        static void ReadBinaryFile(string file, int start, int len)
        {
            using (BinaryReader br = new BinaryReader(File.Open(file, FileMode.Open)))
            {
                int total_len = (int)br.BaseStream.Length, pos = 0;

                if (start >= 0)
                    pos += start;
                else
                    pos = total_len - Math.Abs(start);
                    
                len = pos + len;
                if (len > total_len) return;

                br.BaseStream.Seek(pos, SeekOrigin.Begin);
                while (pos < len)
                {
                    byte by = br.ReadByte();
                    Console.Write("{0,4}", by);
                    pos++;
                }
            }
        }
    }
}

/*
run:
   
read the first 13 bytes

 71  73  70  56  57  97   8  32  10  32 112  32  32

read the last 10 bytes

 32 128 255  32 170  32  32 170  51  32

read from byte 30 5 bytes

 135  32  32  32  32

read from byte 15 30000 bytes

*/

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Answer 2

using System;
using System.IO;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            try
            {
                byte[] barr = null;

                Console.WriteLine("\nread the first 13 bytes\n");
                ReadBinaryFile("d:\\image.gif", 0, 13, ref barr);
                PrintByteArray(barr);
                Console.WriteLine("\n\nread the last 10 bytes\n");
                ReadBinaryFile("d:\\image.gif", -10, 10, ref barr);
                PrintByteArray(barr);
                Console.WriteLine("\n\nread from byte 30 5 bytes \n");
                ReadBinaryFile("d:\\image.gif", 30, 5, ref barr);
                PrintByteArray(barr);
                Console.WriteLine("\n\nread from byte 15 30000 bytes\n");
                ReadBinaryFile("d:\\image.gif", 15, 3000, ref barr);//will show nothing, file size is < 30000
            }
            catch (IOException ioex)
            {
                Console.WriteLine(ioex.Message);
            }
        }
        static void ReadBinaryFile(string file, int start, int len, ref byte[] barr)
        {
            using (BinaryReader br = new BinaryReader(File.Open(file, FileMode.Open)))
            {
                int total_len = (int)br.BaseStream.Length, pos = 0;

                if (start >= 0)
                    pos += start;
                else
                    pos = total_len - Math.Abs(start);
                    
                len = pos + len;
                if (len > total_len) return;

                br.BaseStream.Seek(pos, SeekOrigin.Begin);
                int i = 0;
                barr = new byte[len - pos];
                while (pos++ < len)
                {
                    barr[i++] = br.ReadByte();
                }
            }
        }
        static void PrintByteArray(byte[] barr)
        {
            for (int i = 0; i < barr.Length; i++)
                Console.Write("{0,4}", barr[i]);
        }
    }
}

/*
run:
   
read the first 13 bytes

 71  73  70  56  57  97   8  32  10  32 112  32  32

read the last 10 bytes

 32 128 255  32 170  32  32 170  51  32

read from byte 30 5 bytes

 135  32  32  32  32

read from byte 15 30000 bytes

*/

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