File.OpenRead(String) 方法
定義
重要
部分資訊涉及發行前產品,在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊,不做任何明確或隱含的瑕疵擔保。
開啟現有檔案來讀取。
public:
static System::IO::FileStream ^ OpenRead(System::String ^ path);
public static System.IO.FileStream OpenRead (string path);
static member OpenRead : string -> System.IO.FileStream
Public Shared Function OpenRead (path As String) As FileStream
參數
- path
- String
要被開啟來讀取的檔案。
傳回
指定路徑上的唯讀 FileStream。
例外狀況
.NET Framework 和 2.1 之前的 .NET Core 版本:path
是長度為零的字串、只包含空格符,或包含一或多個無效字元。 您可以使用 GetInvalidPathChars() 方法查詢無效字元。
path
為 null
。
指定的路徑、檔案名稱,或兩者都超出系統定義的長度上限。
指定的路徑無效 (例如,它位於未對應的磁碟機上)。
找不到 path
指定的檔案。
path
格式無效。
開啟檔案時發生 I/O 錯誤。
範例
下列範例會開啟檔案以供讀取。
using namespace System;
using namespace System::IO;
using namespace System::Text;
int main()
{
String^ path = "c:\\temp\\MyTest.txt";
if ( !File::Exists( path ) )
{
// Create the file.
FileStream^ fs = File::Create( path );
try
{
array<Byte>^info = (gcnew UTF8Encoding( true ))->GetBytes( "This is some text in the file." );
// Add some information to the file.
fs->Write( info, 0, info->Length );
}
finally
{
if ( fs )
delete (IDisposable^)fs;
}
}
// Open the stream and read it back.
FileStream^ fs = File::OpenRead( path );
try
{
array<Byte>^b = gcnew array<Byte>(1024);
UTF8Encoding^ temp = gcnew UTF8Encoding( true );
while ( fs->Read( b, 0, b->Length ) > 0 )
{
Console::WriteLine( temp->GetString( b ) );
}
}
finally
{
if ( fs )
delete (IDisposable^)fs;
}
}
using System;
using System.IO;
using System.Text;
class Test
{
public static void Main()
{
string path = @"c:\temp\MyTest.txt";
if (!File.Exists(path))
{
// Create the file.
using (FileStream fs = File.Create(path))
{
Byte[] info = new UTF8Encoding(true).GetBytes("This is some text in the file.");
// Add some information to the file.
fs.Write(info, 0, info.Length);
}
}
// Open the stream and read it back.
using (FileStream fs = File.OpenRead(path))
{
byte[] b = new byte[1024];
UTF8Encoding temp = new UTF8Encoding(true);
while (fs.Read(b,0,b.Length) > 0)
{
Console.WriteLine(temp.GetString(b));
}
}
}
}
open System.IO
open System.Text
let path = @"c:\temp\MyTest.txt"
if File.Exists path |> not then
// Create the file.
use fs = File.Create path
let info =
UTF8Encoding(true)
.GetBytes "This is some text in the file."
// Add some information to the file.
fs.Write(info, 0, info.Length)
// Open the stream and read it back.
do
use fs = File.OpenRead path
let b = Array.zeroCreate 1024
let temp = UTF8Encoding true
while fs.Read(b, 0, b.Length) > 0 do
printfn $"{temp.GetString b}"
Imports System.IO
Imports System.Text
Public Class Test
Public Shared Sub Main()
Dim path As String = "c:\temp\MyTest.txt"
If Not File.Exists(path) Then
' Create the file.
Using fs As FileStream = File.Create(path)
Dim info As Byte() = New UTF8Encoding(True).GetBytes("This is some text in the file.")
' Add some information to the file.
fs.Write(info, 0, info.Length)
End Using
End If
' Open the stream and read it back.
Using fs As FileStream = File.OpenRead(path)
Dim b(1023) As Byte
Dim temp As UTF8Encoding = New UTF8Encoding(True)
Do While fs.Read(b, 0, b.Length) > 0
Console.WriteLine(temp.GetString(b))
Loop
End Using
End Sub
End Class
備註
這個方法相當於 FileStream(String, FileMode, FileAccess, FileShare) 建構函式多載, FileMode 其值為 Open、 FileAccess 值 Read 和 FileShare 的值 Read。
允許 path
參數指定相對路徑或絕對路徑資訊。 相對路徑資訊會解譯為相對於目前的工作目錄。 若要取得目前的工作目錄,請參閱 GetCurrentDirectory。
如需一般 I/O 工作的清單,請參閱 一般 I/O 工作。