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FileStream.Read Method

Reads a block of bytes from the stream and writes the data in a given buffer.

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

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


Type: System.Byte[]

When this method returns, contains the specified byte array with the values between offset and (offset + count - 1) replaced by the bytes read from the current source.

Type: System.Int32

The byte offset in array at which the read bytes will be placed.

Type: System.Int32

The maximum number of bytes to read.

Return Value

Type: System.Int32
The total number of bytes read into the buffer. This might be less than the number of bytes requested if that number of bytes are not currently available, or zero if the end of the stream is reached.


array is null.


offset or count is negative.


The stream does not support reading.


An I/O error occurs.


offset and count describe an invalid range in array.


Methods were called after the stream was closed.

This method overrides Read.

The offset parameter gives the offset of the byte in array (the buffer index) at which to begin reading, and the count parameter gives the maximum number of bytes to be read from this stream. The returned value is the actual number of bytes read, or zero if the end of the stream is reached. If the read operation is successful, the current position of the stream is advanced by the number of bytes read. If an exception occurs, the current position of the stream is unchanged.

The Read method returns zero only after reaching the end of the stream. Otherwise, Read always reads at least one byte from the stream before returning. If no data is available from the stream upon a call to Read, the method will block until at least one byte of data can be returned. An implementation is free to return fewer bytes than requested even if the end of the stream has not been reached.

Use BinaryReader for reading primitive data types.

Do not interrupt a thread that is performing a read operation. Although the operation may appear to be successful after the thread is unblocked, the interruption can affect your application's performance and reliability.

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

The following example reads the contents of a FileStream object and writes it into another FileStream object.

using System;
using System.IO;

class Test

public static void Main()
    // Specify a file to read from and to create.
    string pathSource = @"c:\tests\source.txt";
    string pathNew = @"c:\tests\newfile.txt";


        using (FileStream fsSource = new FileStream(pathSource,
            FileMode.Open, FileAccess.Read))

            // Read the source file into a byte array.
            byte[] bytes = new byte[fsSource.Length];
            int numBytesToRead = (int)fsSource.Length;
            int numBytesRead = 0;
            while (numBytesToRead > 0)
                // Read may return anything from 0 to numBytesToRead. 
                int n = fsSource.Read(bytes, numBytesRead, numBytesToRead);

                // Break when the end of the file is reached. 
                if (n == 0)

                numBytesRead += n;
                numBytesToRead -= n;
             numBytesToRead = bytes.Length;

            // Write the byte array to the other FileStream. 
            using (FileStream fsNew = new FileStream(pathNew,
                FileMode.Create, FileAccess.Write))
                fsNew.Write(bytes, 0, numBytesToRead);
    catch (FileNotFoundException ioEx)

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

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

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0





Revised the code example to show reading the entire stream.