File.OpenRead Method (String)

 
System_CAPS_noteNote

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Opens an existing file for reading.

Namespace:   System.IO
Assembly:  mscorlib (in mscorlib.dll)

Public Shared Function OpenRead (
	path As String
) As FileStream

Parameters

path
Type: System.String

The file to be opened for reading.

Return Value

Type: System.IO.FileStream

A read-only FileStream on the specified path.

Exception Condition
ArgumentException

path is a zero-length string, contains only white space, or contains one or more invalid characters as defined by InvalidPathChars.

ArgumentNullException

path is null.

PathTooLongException

The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must be less than 248 characters, and file names must be less than 260 characters.

DirectoryNotFoundException

The specified path is invalid, (for example, it is on an unmapped drive).

UnauthorizedAccessException

path specified a directory.

-or-

The caller does not have the required permission.

FileNotFoundException

The file specified in path was not found.

NotSupportedException

path is in an invalid format.

IOException

An I/O error occurred while opening the file.

This method is equivalent to the FileStream(String, FileMode, FileAccess, FileShare) constructor overload with a FileMode value of Open, a FileAccess value of Read and a FileShare value of Read.

The path parameter is permitted to specify relative or absolute path information. Relative path information is interpreted as relative to the current working directory. To obtain the current working directory, see GetCurrentDirectory.

For a list of common I/O tasks, see Common I-O Tasks.

The following example opens a file for reading.

Imports System
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(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
    End Using

  End Sub
End Class

FileIOPermission

for reading from the specified file. Associated enumeration: FileIOPermissionAccess.Read

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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