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FileStream.Seek Method (Int64, SeekOrigin)


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Sets the current position of this stream to the given value.

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

public override long Seek(
	long offset,
	SeekOrigin origin


Type: System.Int64

The point relative to origin from which to begin seeking.

Type: System.IO.SeekOrigin

Specifies the beginning, the end, or the current position as a reference point for offset, using a value of type SeekOrigin.

Return Value

Type: System.Int64

The new position in the stream.

Exception Condition

An I/O error occurred.


The stream does not support seeking, such as if the FileStream is constructed from a pipe or console output.


Seeking is attempted before the beginning of the stream.


Methods were called after the stream was closed.

This method overrides Stream.Seek.


Use the FileStream.CanSeek property to determine whether the current instance supports seeking. For additional information, see Stream.CanSeek.

You can seek to any location beyond the length of the stream. When you seek beyond the length of the file, the file size grows. In Windows NT and later versions, data added to the end of the file is set to zero. In Windows 98 or earlier versions, data added to the end of the file is not set to zero, which means that previously deleted data is visible to the stream.

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

The following example shows how to write data to a file, byte by byte, and then verify that the data was written correctly.

using System;
using System.IO;

class FStream
    static void Main()
        const string fileName = "Test#@@#.dat";

        // Create random data to write to the file.
        byte[] dataArray = new byte[100000];
        new Random().NextBytes(dataArray);

            fileStream = new FileStream(fileName, FileMode.Create))
            // Write the data to the file, byte by byte.
            for(int i = 0; i < dataArray.Length; i++)

            // Set the stream position to the beginning of the file.
            fileStream.Seek(0, SeekOrigin.Begin);

            // Read and verify the data.
            for(int i = 0; i < fileStream.Length; i++)
                if(dataArray[i] != fileStream.ReadByte())
                    Console.WriteLine("Error writing data.");
            Console.WriteLine("The data was written to {0} " +
                "and verified.", fileStream.Name);

The following example reads text in the reverse direction, from the end of file to the beginning of the file, by using the various SeekOrigin values with the Seek method.

using System;
using System.IO;

public class FSSeek
    public static void Main()
        long offset;
        int nextByte;

        // alphabet.txt contains "abcdefghijklmnopqrstuvwxyz"
        using (FileStream fs = new FileStream(@"c:\temp\alphabet.txt", FileMode.Open, FileAccess.Read))
            for (offset = 1; offset <= fs.Length; offset++)
                fs.Seek(-offset, SeekOrigin.End);

            fs.Seek(20, SeekOrigin.Begin);

            while ((nextByte = fs.ReadByte()) > 0)
// This code example displays the following output:
// zyxwvutsrqponmlkjihgfedcba
// uvwxyz

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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