BinaryWriter.Seek(Int32, SeekOrigin) Metodo
Definizione
Importante
Alcune informazioni sono relative alla release non definitiva del prodotto, che potrebbe subire modifiche significative prima della release definitiva. Microsoft non riconosce alcuna garanzia, espressa o implicita, in merito alle informazioni qui fornite.
Imposta la posizione all'interno del flusso corrente.
public:
virtual long Seek(int offset, System::IO::SeekOrigin origin);public virtual long Seek (int offset, System.IO.SeekOrigin origin);abstract member Seek : int * System.IO.SeekOrigin -> int64
override this.Seek : int * System.IO.SeekOrigin -> int64Public Overridable Function Seek (offset As Integer, origin As SeekOrigin) As LongParametri
- offset
- Int32
Offset dei byte relativo a origin.
- origin
- SeekOrigin
Campo di SeekOrigin che indica il punto di riferimento dal quale ottenere la nuova posizione.
Restituisce
Posizione all'interno del flusso corrente.
Eccezioni
Il puntatore al file è stato spostato in un percorso non valido.
Il valore SeekOrigin non è valido.
Esempio
L'esempio seguente scrive una serie di valori di byte in un file. Nell'esempio viene Seek usato per passare a diversi percorsi nel file e quindi scrivere byte marcatori usando il Write metodo .
using namespace System;
using namespace System::IO;
using namespace System::Text;
public ref class BinReadWrite
{
public:
static void Main()
{
String^ testfile = "C:\\temp\\testfile.bin";
// create a test file using BinaryWriter
FileStream^ fs = File::Create(testfile);
UTF8Encoding^ utf8 = gcnew UTF8Encoding();
BinaryWriter^ bw = gcnew BinaryWriter(fs, utf8);
// write a series of bytes to the file, each time incrementing
// the value from 0 - 127
int pos;
for (pos = 0; pos < 128; pos++)
{
bw->Write((Byte)pos);
}
// reset the stream position for the next write pass
bw->Seek(0, SeekOrigin::Begin);
// write marks in file with the value of 255 going forward
for (pos = 0; pos < 120; pos += 8)
{
bw->Seek(7, SeekOrigin::Current);
bw->Write((Byte)255);
}
// reset the stream position for the next write pass
bw->Seek(0, SeekOrigin::End);
// write marks in file with the value of 254 going backward
for (pos = 128; pos > 6; pos -= 6)
{
bw->Seek(-6, SeekOrigin::Current);
bw->Write((Byte)254);
bw->Seek(-1, SeekOrigin::Current);
}
// now dump the contents of the file using the original file stream
fs->Seek(0, SeekOrigin::Begin);
array<Byte>^ rawbytes = gcnew array<Byte>(fs->Length);
fs->Read(rawbytes, 0, (int)fs->Length);
int i = 0;
for each (Byte b in rawbytes)
{
switch (b)
{
case 254:
{
Console::Write("-%- ");
}
break;
case 255:
{
Console::Write("-*- ");
}
break;
default:
{
Console::Write("{0:d3} ", b);
}
break;
}
i++;
if (i == 16)
{
Console::WriteLine();
i = 0;
}
}
fs->Close();
}
};
int main()
{
BinReadWrite::Main();
}
//The output from the program is this:
//
// 000 001 -%- 003 004 005 006 -*- -%- 009 010 011 012 013 -%- -*-
// 016 017 018 019 -%- 021 022 -*- 024 025 -%- 027 028 029 030 -*-
// -%- 033 034 035 036 037 -%- -*- 040 041 042 043 -%- 045 046 -*-
// 048 049 -%- 051 052 053 054 -*- -%- 057 058 059 060 061 -%- -*-
// 064 065 066 067 -%- 069 070 -*- 072 073 -%- 075 076 077 078 -*-
// -%- 081 082 083 084 085 -%- -*- 088 089 090 091 -%- 093 094 -*-
// 096 097 -%- 099 100 101 102 -*- -%- 105 106 107 108 109 -%- -*-
// 112 113 114 115 -%- 117 118 -*- 120 121 -%- 123 124 125 126 127
using System;
using System.IO;
using System.Text;
public class BinReadWrite3
{
public static void Main()
{
string testfile = @"C:\temp\testfile.bin";
// create a test file using BinaryWriter
FileStream fs = File.Create(testfile);
UTF8Encoding utf8 = new UTF8Encoding();
BinaryWriter bw = new BinaryWriter(fs, utf8);
// write a series of bytes to the file, each time incrementing
// the value from 0 - 127
int pos;
for (pos = 0; pos < 128; pos++)
{
bw.Write((byte)pos);
}
// reset the stream position for the next write pass
bw.Seek(0, SeekOrigin.Begin);
// write marks in file with the value of 255 going forward
for (pos = 0; pos < 120; pos += 8)
{
bw.Seek(7, SeekOrigin.Current);
bw.Write((byte)255);
}
// reset the stream position for the next write pass
bw.Seek(0, SeekOrigin.End);
// write marks in file with the value of 254 going backward
for (pos = 128; pos > 6; pos -= 6)
{
bw.Seek(-6, SeekOrigin.Current);
bw.Write((byte)254);
bw.Seek(-1, SeekOrigin.Current);
}
// now dump the contents of the file using the original file stream
fs.Seek(0, SeekOrigin.Begin);
byte[] rawbytes = new byte[fs.Length];
fs.Read(rawbytes, 0, (int)fs.Length);
int i = 0;
foreach (byte b in rawbytes)
{
switch (b)
{
case 254:
{
Console.Write("-%- ");
}
break;
case 255:
{
Console.Write("-*- ");
}
break;
default:
{
Console.Write("{0:d3} ", b);
}
break;
}
i++;
if (i == 16)
{
Console.WriteLine();
i = 0;
}
}
fs.Close();
}
}
//The output from the program is this:
//
// 000 001 -%- 003 004 005 006 -*- -%- 009 010 011 012 013 -%- -*-
// 016 017 018 019 -%- 021 022 -*- 024 025 -%- 027 028 029 030 -*-
// -%- 033 034 035 036 037 -%- -*- 040 041 042 043 -%- 045 046 -*-
// 048 049 -%- 051 052 053 054 -*- -%- 057 058 059 060 061 -%- -*-
// 064 065 066 067 -%- 069 070 -*- 072 073 -%- 075 076 077 078 -*-
// -%- 081 082 083 084 085 -%- -*- 088 089 090 091 -%- 093 094 -*-
// 096 097 -%- 099 100 101 102 -*- -%- 105 106 107 108 109 -%- -*-
// 112 113 114 115 -%- 117 118 -*- 120 121 -%- 123 124 125 126 127
open System.IO
open System.Text
let testfile = @"C:\temp\testfile.bin"
// create a test file using BinaryWriter
let fs = File.Create testfile
let utf8 = UTF8Encoding()
let bw = new BinaryWriter(fs, utf8)
// write a series of bytes to the file, each time incrementing
// the value from 0 - 127
for pos = 0 to 127 do
bw.Write(byte pos)
// reset the stream position for the next write pass
bw.Seek(0, SeekOrigin.Begin) |> ignore
// write marks in file with the value of 255 going forward
for _ in 0..8..119 do
bw.Seek(7, SeekOrigin.Current) |> ignore
bw.Write(byte 255)
// reset the stream position for the next write pass
bw.Seek(0, SeekOrigin.End) |> ignore
// write marks in file with the value of 254 going backward
for _ in 128 .. -6 .. 6 do
bw.Seek(-6, SeekOrigin.Current) |> ignore
bw.Write(byte 254)
bw.Seek(-1, SeekOrigin.Current) |> ignore
// now dump the contents of the file using the original file stream
fs.Seek(0, SeekOrigin.Begin) |> ignore
let rawbytes = Array.zeroCreate<byte> (int fs.Length)
fs.Read(rawbytes, 0, int fs.Length) |> ignore
let mutable i = 0
for b in rawbytes do
match b with
| 254uy ->
printf "-%%- "
| 255uy ->
printf "-*- "
| _ ->
printf $"{b:d3} "
i <- i + 1
if i = 16 then
printfn ""
i <- 0
fs.Close()
//The output from the program is this:
//
// 000 001 -%- 003 004 005 006 -*- -%- 009 010 011 012 013 -%- -*-
// 016 017 018 019 -%- 021 022 -*- 024 025 -%- 027 028 029 030 -*-
// -%- 033 034 035 036 037 -%- -*- 040 041 042 043 -%- 045 046 -*-
// 048 049 -%- 051 052 053 054 -*- -%- 057 058 059 060 061 -%- -*-
// 064 065 066 067 -%- 069 070 -*- 072 073 -%- 075 076 077 078 -*-
// -%- 081 082 083 084 085 -%- -*- 088 089 090 091 -%- 093 094 -*-
// 096 097 -%- 099 100 101 102 -*- -%- 105 106 107 108 109 -%- -*-
// 112 113 114 115 -%- 117 118 -*- 120 121 -%- 123 124 125 126 127
Imports System.IO
Imports System.Text
Public Class BinReadWrite
Public Shared Sub Main()
Dim testfile As String = "C:\temp\testfile.bin"
' create a test file using BinaryWriter
Dim fs As FileStream = File.Create(testfile)
Dim utf8 As New UTF8Encoding()
Dim bw As New BinaryWriter(fs, utf8)
' write a series of bytes to the file, each time incrementing
' the value from 0 - 127
Dim pos As Integer
For pos = 0 to 127
bw.Write(CType(pos, Byte))
Next pos
' reset the stream position for the next write pass
bw.Seek(0, SeekOrigin.Begin)
' write marks in file with the value of 255 going forward
For pos = 0 To 119 Step 8
bw.Seek(7, SeekOrigin.Current)
bw.Write(CType(255, Byte))
Next pos
' reset the stream position for the next write pass
bw.Seek(0, SeekOrigin.End)
' write marks in file with the value of 254 going backward
For pos = 128 To 7 Step -6
bw.Seek(-6, SeekOrigin.Current)
bw.Write(CType(254, Byte))
bw.Seek(-1, SeekOrigin.Current)
Next pos
' now dump the contents of the file using the original file stream
fs.Seek(0, SeekOrigin.Begin)
Console.WriteLine("Length: {0:d}", fs.Length)
Dim rawbytes(fs.Length) As Byte
fs.Read(rawbytes, 0, fs.Length)
Console.WriteLine("Length: {0:d}", rawbytes.Length)
Dim i As Integer = 0
For Each b As Byte In rawbytes
Select b
Case 254
Console.Write("-%- ")
Case 255
Console.Write("-*- ")
Case Else
Console.Write("{0:d3} ", b)
End Select
i = i + 1
If i = 16 Then
Console.WriteLine()
i = 0
End If
Next b
fs.Close()
End Sub
End Class
' The output from the program is this:
'
' 000 001 -%- 003 004 005 006 -*- -%- 009 010 011 012 013 -%- -*-
' 016 017 018 019 -%- 021 022 -*- 024 025 -%- 027 028 029 030 -*-
' -%- 033 034 035 036 037 -%- -*- 040 041 042 043 -%- 045 046 -*-
' 048 049 -%- 051 052 053 054 -*- -%- 057 058 059 060 061 -%- -*-
' 064 065 066 067 -%- 069 070 -*- 072 073 -%- 075 076 077 078 -*-
' -%- 081 082 083 084 085 -%- -*- 088 089 090 091 -%- 093 094 -*-
' 096 097 -%- 099 100 101 102 -*- -%- 105 106 107 108 109 -%- -*-
' 112 113 114 115 -%- 117 118 -*- 120 121 -%- 123 124 125 126 127
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