FileStream.Seek(Int64, SeekOrigin) 方法
定义
重要
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将该流的当前位置设置为给定值。
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 Long参数
- offset
- Int64
相对于 origin 的点，从此处开始查找。
- origin
- SeekOrigin
使用 SeekOrigin 类型的值，将开始位置、结束位置或当前位置指定为 offset 的参考点。
返回
流中的新位置。
例外
出现 I/O 错误。
该流不支持查找，例如如果 FileStream 是从管道或控制台输出构造的，则不支持查找。
试图在流的开始位置之前进行查找。
在流关闭后调用方法。
示例
以下示例演示如何将数据逐字节写入文件，然后验证数据是否已正确写入。
using namespace System;
using namespace System::IO;
int main()
{
String^ fileName = "Test@##@.dat";
// Create random data to write to the file.
array<Byte>^dataArray = gcnew array<Byte>(100000);
(gcnew Random)->NextBytes( dataArray );
FileStream^ fileStream = gcnew FileStream( fileName,FileMode::Create );
try
{
// 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 -1;
}
}
Console::WriteLine( "The data was written to {0} "
"and verified.", fileStream->Name );
}
finally
{
fileStream->Close();
}
}
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
以下示例将各种 SeekOrigin 值与 方法结合使用 Seek ，以相反方向读取文本，从文件末尾到文件开头。
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
注解
此方法重写 Stream.Seek。
注意
FileStream.CanSeek使用 属性确定当前实例是否支持查找。 有关附加信息，请参见 Stream.CanSeek。
可以查找超出流长度的任何位置。 当查找超出文件长度时，文件大小会增大。 添加到文件末尾的数据设置为零。
有关常见文件和目录操作的列表，请参阅 常见 I/O 任务。
