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FileInfo.OpenRead Method

Creates a read-only FileStream.

[Visual Basic]
Public Function OpenRead() As FileStream
[C#]
public FileStream OpenRead();
[C++]
public: FileStream* OpenRead();
[JScript]
public function OpenRead() : FileStream;

Return Value

A new read-only FileStream object.

Exceptions

Exception Type Condition
UnauthorizedAccessException path is read-only or is a directory.
DirectoryNotFoundException The specified path is invalid, such as being on an unmapped drive.
IOException The file is already open.

Remarks

For an example of using this method, see the Example section below. The following table lists examples of other typical or related I/O tasks.

To do this... See the example in this topic...
Create a text file. Writing Text to a File
Write to a text file. Writing Text to a File
Read from a text file. Reading Text from a File
Append text to a file. Opening and Appending to a Log File

File.AppendText

FileInfo.AppendText

Rename or move a file. File.Move

FileInfo.MoveTo

Copy a file. File.Copy

FileInfo.CopyTo

Get the size of a file. FileInfo.Length
Get the attributes of a file. File.GetAttributes
Set the attributes of a file. File.SetAttributes
Determine if a file exists. File.Exists
Read from a binary file. Reading and Writing to a Newly Created Data File
Write to a binary file. Reading and Writing to a Newly Created Data File
Create a directory. CreateDirectory

Directory

Example

[Visual Basic, C#, C++] The following example opens a file as read-only and reads from it.

[Visual Basic] 
Imports System
Imports System.IO
Imports System.Text

Public Class Test

    Public Shared Sub Main()
        Dim path As String = "c:\temp\MyTest.txt"
        Dim fi As FileInfo = New FileInfo(path)
        Dim fs As FileStream

        ' Delete the file if it exists.
        If fi.Exists = False Then
            'Create the file.
            fs = fi.Create()
            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)
            fs.Close()
        End If

        'Open the stream and read it back.
        fs = fi.OpenRead()
        Dim b(1024) As Byte
        Dim temp As UTF8Encoding = New UTF8Encoding(True)

        Do While fs.Read(b, 0, b.Length) > 0
            Console.WriteLine(temp.GetString(b))
        Loop
        fs.Close()
    End Sub
End Class

[C#] 
using System;
using System.IO;
using System.Text;

class Test 
{
    
    public static void Main() 
    {
        string path = @"c:\temp\MyTest.txt";
        FileInfo fi = new FileInfo(path);

        // Delete the file if it exists.
        if (!fi.Exists) 
        {
            //Create the file.
            using (FileStream fs = fi.Create()) 
            {
                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 = fi.OpenRead()) 
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b,0,b.Length) > 0) 
            {
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}

[C++] 
#using <mscorlib.dll>

using namespace System;
using namespace System::IO;
using namespace System::Text;

int main() {
    String* path = S"c:\\temp\\MyTest.txt";
    FileInfo* fi = new FileInfo(path);

    // Delete the file if it exists.
    if (!fi->Exists) {
        //Create the file.
        FileStream* fs = fi->Create();
        try {
            Byte info[] = (new UTF8Encoding(true))->GetBytes(S"This is some text in the file.");
            //Add some information to the file.
            fs->Write(info, 0, info->Length);
        } __finally {
            if (fs) __try_cast<IDisposable*>(fs)->Dispose();
        }
    }

    //Open the stream and read it back.
    FileStream* fs = fi->OpenRead();
    try {
        Byte b[] = new Byte[1024];
        UTF8Encoding* temp = new UTF8Encoding(true);

        while (fs->Read(b,0,b->Length) > 0) {
            Console::WriteLine(temp->GetString(b));
        }
    } __finally {
        if (fs) __try_cast<IDisposable*>(fs)->Dispose();
    }
}

[JScript] No example is available for JScript. To view a Visual Basic, C#, or C++ example, click the Language Filter button Language Filter in the upper-left corner of the page.

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework

.NET Framework Security: 

See Also

FileInfo Class | FileInfo Members | System.IO Namespace | Working with I/O | Reading Text from a File | Writing Text to a File | Basic File I/O | Reading and Writing to a Newly Created Data File

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