FileStream.Seek(Int64, SeekOrigin) Method
Definition
Important
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Sets the current position of this stream to the given value.
public:
override long Seek(long offset, System::IO::SeekOrigin origin);public override long Seek(long offset, System.IO.SeekOrigin origin);override this.Seek : int64 * System.IO.SeekOrigin -> int64Public Overrides Function Seek (offset As Long, origin As SeekOrigin) As LongParameters
- offset
- Int64
The point relative to origin from which to begin seeking.
- origin
- SeekOrigin
Specifies the beginning, the end, or the current position as a reference point for offset, using a value of type SeekOrigin.
Returns
The new position in the stream.
Exceptions
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.
Examples
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);
using(FileStream
fileStream = new FileStream(fileName, FileMode.Create))
{
// Write the data to the file, byte by byte.
for(int i = 0; i < dataArray.Length; i++)
{
fileStream.WriteByte(dataArray[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.");
return;
}
}
Console.WriteLine("The data was written to {0} " +
"and verified.", fileStream.Name);
}
}
}
open System
open System.IO
let fileName = "Test#@@#.dat"
// Create random data to write to the file.
let dataArray = Array.zeroCreate 100000
Random.Shared.NextBytes dataArray
do
use fileStream = new FileStream(fileName, FileMode.Create)
// Write the data to the file, byte by byte.
for i = 0 to dataArray.Length - 1 do
fileStream.WriteByte dataArray[i]
// Set the stream position to the beginning of the file.
fileStream.Seek(0, SeekOrigin.Begin) |> ignore
// Read and verify the data.
for i in 0L .. fileStream.Length - 1L do
if dataArray[int i] <> (fileStream.ReadByte() |> byte) then
printfn "Error writing data."
exit 1
printfn $"The data was written to {fileStream.Name} and verified."
Imports System.IO
Imports System.Text
Class FStream
Shared Sub Main()
Const fileName As String = "Test#@@#.dat"
' Create random data to write to the file.
Dim dataArray(100000) As Byte
Dim randomGenerator As New Random()
randomGenerator.NextBytes(dataArray)
Dim fileStream As FileStream = _
new FileStream(fileName, FileMode.Create)
Try
' Write the data to the file, byte by byte.
For i As Integer = 0 To dataArray.Length - 1
fileStream.WriteByte(dataArray(i))
Next i
' Set the stream position to the beginning of the stream.
fileStream.Seek(0, SeekOrigin.Begin)
' Read and verify the data.
For i As Integer = 0 To _
CType(fileStream.Length, Integer) - 1
If dataArray(i) <> fileStream.ReadByte() Then
Console.WriteLine("Error writing data.")
Return
End If
Next i
Console.WriteLine("The data was written to {0} " & _
"and verified.", fileStream.Name)
Finally
fileStream.Close()
End Try
End Sub
End Class
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);
Console.Write((char)fs.ReadByte());
}
Console.WriteLine();
fs.Seek(20, SeekOrigin.Begin);
while ((nextByte = fs.ReadByte()) > 0)
{
Console.Write((char)nextByte);
}
Console.WriteLine();
}
}
}
// This code example displays the following output:
//
// zyxwvutsrqponmlkjihgfedcba
// uvwxyz
open System.IO
// alphabet.txt contains "abcdefghijklmnopqrstuvwxyz"
using (new FileStream(@"c:\temp\alphabet.txt", FileMode.Open, FileAccess.Read)) (fun fs ->
for offset in 1L .. fs.Length do
fs.Seek(-offset, SeekOrigin.End) |> ignore
printf $"{fs.ReadByte() |> char}"
printfn ""
fs.Seek(20, SeekOrigin.Begin) |> ignore
let mutable nextByte = fs.ReadByte()
while nextByte > 0 do
printf $"{char nextByte}"
nextByte <- fs.ReadByte())
// This code example displays the following output:
//
// zyxwvutsrqponmlkjihgfedcba
// uvwxyz
Imports System.IO
Public Class FSSeek
Public Shared Sub Main()
Dim offset As Long
Dim nextByte As Integer
' alphabet.txt contains "abcdefghijklmnopqrstuvwxyz"
Using fs As New FileStream("c:\temp\alphabet.txt", FileMode.Open, FileAccess.Read)
For offset = 1 To fs.Length
fs.Seek(-offset, SeekOrigin.End)
Console.Write(Convert.ToChar(fs.ReadByte()))
Next offset
Console.WriteLine()
fs.Seek(20, SeekOrigin.Begin)
nextByte = fs.ReadByte()
While (nextByte > 0)
Console.Write(Convert.ToChar(nextByte))
nextByte = fs.ReadByte()
End While
Console.WriteLine()
End Using
End Sub
End Class
' This code example displays the following output:
'
' zyxwvutsrqponmlkjihgfedcba
' uvwxyz
Remarks
This method overrides Stream.Seek.
Note
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. Data added to the end of the file is set to zero.
For a list of common file and directory operations, see Common I/O Tasks.
