BinaryReader.ReadBytes(Int32) Method

Definition

Namespace:

System.IO

Assemblies:

netstandard.dll, System.Runtime.dll

Source:

BinaryReader.cs

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

C#

public virtual byte[] ReadBytes(int count);

Parameters

count

Int32

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

Returns

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.

Exceptions

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 occurred.

ObjectDisposedException

The stream is closed.

ArgumentOutOfRangeException

count is negative.

Examples

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.

C#

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.

C#

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);
        }
    }
}

Remarks

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.

Applies to

See also

• File and Stream I/O
• How to: Read Text from a File
• How to: Write Text to a File