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FileInfo.Open Method (FileMode, FileAccess)

Opens a file in the specified mode with read, write, or read/write access.

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

public FileStream Open(
	FileMode mode,
	FileAccess access
)

Parameters

mode
Type: System.IO.FileMode

A FileMode constant specifying the mode (for example, Open or Append) in which to open the file.

access
Type: System.IO.FileAccess

A FileAccess constant specifying whether to open the file with Read, Write, or ReadWrite file access.

Return Value

Type: System.IO.FileStream
A FileStream object opened in the specified mode and access, and unshared.

ExceptionCondition
SecurityException

The caller does not have the required permission.

FileNotFoundException

The file is not found.

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.

The following example opens a file as read-only and reads from the file.

using System;
using System.IO;
using System.Text;

class Test 
{
	
    public static void Main() 
    {
        string path = @"c:\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.Open(FileMode.Open, FileAccess.Read)) 
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);
            while (fs.Read(b,0,b.Length) > 0) 
            {
                Console.WriteLine(temp.GetString(b));
            }

            try 
            {
                //Try to write to the file.
                fs.Write(b,0,b.Length);
            } 
            catch (Exception e) 
            {
                Console.WriteLine("Writing was disallowed, as expected: {0}",
                    e.ToString());
            }
        }
    }
}
//This code produces output similar to the following;  
//results may vary based on the computer/file structure/etc.: 
// 
//This is some text in the file. 
// 
// 
// 
// 
// 
// 
// 
// 
// 
// 
// 
// 
//Writing was disallowed, as expected: System.NotSupportedException: Stream does  
//not support writing. 
//   at System.IO.__Error.WriteNotSupported() 
//   at System.IO.FileStream.Write(Byte[] array, Int32 offset, Int32 count) 
//   at Test.Main() in C:\Documents and Settings\My Computer\My Documents\ 
//Visual Studio 2005\Projects\finfo open2\finfo open2\Program.cs:line 39

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

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