Read Method

FileStream.Read Method (Byte[], Int32, Int32)


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.

Exception Condition

array is null.


offset or count is negative.


The stream does not support reading.


An I/O error occurred.


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 application may appear to run successfully after the thread is unblocked, the interruption can decrease your application's performance and reliability.

For a list of common file and directory operations, see Common I/O Tasks.

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

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)

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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