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BinaryReader.ReadBytes Method

Reads the specified number of bytes from the current stream into a byte array and advances the current position by that number of bytes.

Namespace:  System.IO
Assembly:  mscorlib (in mscorlib.dll)

public virtual byte[] ReadBytes(
	int count
)

Parameters

count
Type: System.Int32

The number of bytes to read. This value must be 0 or a non-negative number or an exception will occur.

Return Value

Type: System.Byte[]
A byte array containing data read from the underlying stream. This might be less than the number of bytes requested if the end of the stream is reached.

ExceptionCondition
ArgumentException

The number of decoded characters to read is greater than count. This can happen if a Unicode decoder returns fallback characters or a surrogate pair.

IOException

An I/O error occurs.

ObjectDisposedException

The stream is closed.

ArgumentOutOfRangeException

count is negative.

BinaryReader does not restore the file position after an unsuccessful read operation.

For a list of common I/O tasks, see Common I/O Tasks.

The following code example shows how to write binary data using memory as a backing store, and then verify that the data was written correctly.

using System;
using System.IO;

class BinaryRW
{
    static void Main()
    {
        const int arrayLength = 1000;

        // Create random data to write to the stream. 
        byte[] dataArray = new byte[arrayLength];
        new Random().NextBytes(dataArray);

        BinaryWriter binWriter = new BinaryWriter(new MemoryStream());

        // Write the data to the stream.
        Console.WriteLine("Writing the data.");
        binWriter.Write(dataArray);

        // Create the reader using the stream from the writer.
        BinaryReader binReader = 
            new BinaryReader(binWriter.BaseStream);

        // Set Position to the beginning of the stream.
        binReader.BaseStream.Position = 0;

        // Read and verify the data. 
        byte[] verifyArray = binReader.ReadBytes(arrayLength);
        if(verifyArray.Length != arrayLength)
        {
            Console.WriteLine("Error writing the data.");
            return;
        }
        for(int i = 0; i < arrayLength; i++)
        {
            if(verifyArray[i] != dataArray[i])
            {
                Console.WriteLine("Error writing the data.");
                return;
            }
        }
        Console.WriteLine("The data was written and verified.");
    }
}

This example reads the contents of a file and displays it to the console as dump text. The end of the file that is being read is detected when the length of the Byte array returned from ReadBytes is zero.

using System;
using System.IO;
using System.Text;

public class DumpFileSample
{
    private static readonly int CHUNK_SIZE = 1024;
    public static void Main(String[] args)
    {
        if ((args.Length == 0) || !File.Exists(args[0]))
        {
            Console.WriteLine("Please provide an existing file name.");
        }
        else
        {
            using (FileStream fs = new FileStream(args[0], FileMode.Open, FileAccess.Read))
            {
                using (BinaryReader br = new BinaryReader(fs, new ASCIIEncoding()))
                {
                    byte[] chunk;

                    chunk = br.ReadBytes(CHUNK_SIZE);
                    while(chunk.Length > 0)
                    {
                        DumpBytes(chunk, chunk.Length);
                        chunk = br.ReadBytes(CHUNK_SIZE);
                    }
                }
            }
        }
    }

    public static void DumpBytes(byte[] bdata, int len)
    {
        int i;
        int j = 0;
        char dchar;
        // 3 * 16 chars for hex display, 16 chars for text and 8 chars 
        // for the 'gutter' int the middle.
        StringBuilder dumptext = new StringBuilder("        ", 16 * 4 + 8);
        for (i = 0; i < len; i++)
        {
            dumptext.Insert(j * 3, String.Format("{0:X2} ", (int)bdata[i]));
            dchar = (char)bdata[i];
            //' replace 'non-printable' chars with a '.'. 
            if (Char.IsWhiteSpace(dchar) || Char.IsControl(dchar))
            {
                dchar = '.';
            }
            dumptext.Append(dchar);
            j++;
            if (j == 16)
            {
                Console.WriteLine(dumptext);
                dumptext.Length = 0;
                dumptext.Append("        ");
                j = 0;
            }
        }
        // display the remaining line 
        if (j > 0)
        {
            for (i = j; i < 16; i++)
            {
                dumptext.Insert(j * 3, "   ");
            }
            Console.WriteLine(dumptext);
        }
    }
}

.NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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