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File.Open Method (String, FileMode, FileAccess)

Opens a FileStream on the specified path, with the specified mode and access.

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

public static FileStream Open (
	string path,
	FileMode mode,
	FileAccess access
)
public static FileStream Open (
	String path, 
	FileMode mode, 
	FileAccess access
)
public static function Open (
	path : String, 
	mode : FileMode, 
	access : FileAccess
) : FileStream

Parameters

path

The file to open.

mode

A FileMode value that specifies whether a file is created if one does not exist, and determines whether the contents of existing files are retained or overwritten.

access

A FileAccess value that specifies the operations that can be performed on the file.

Return Value

An unshared FileStream that provides access to the specified file, with the specified mode and access.

Exception typeCondition

ArgumentException

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

-or-

access specified Read and mode specified Create, CreateNew, Truncate, or Append.

ArgumentNullException

path is a null reference (Nothing in Visual Basic).

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).

IOException

An I/O error occurred while opening the file.

UnauthorizedAccessException

path specified a file that is read-only and access is not Read.

-or-

path specified a directory.

-or-

The caller does not have the required permission.

ArgumentOutOfRangeException

mode or access specified an invalid value.

FileNotFoundException

The file specified in path was not found.

NotSupportedException

path is in an invalid format.

This method is equivalent to the FileStream(String,FileMode,FileAccess,FileShare) constructor overload.

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 an example of using this method, see the Example section. 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.

How to: Write Text to a File

Write to a text file.

How to: Write Text to a File

Read from a text file.

How to: Read Text from a File

Append text to a file.

How to: Open and Append 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.

How to: Read and Write to a Newly Created Data File

Write to a binary file.

How to: Read and Write to a Newly Created Data File

Create a directory.

CreateDirectory

Directory

The following example opens a file with read-only access.

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

class Test 
{
    public static void Main() 
    {
        // This sample assumes that you have a folder named "c:\temp" on your computer.
        string filePath = @"c:\temp\MyTest.txt";

        // Delete the file if it exists.
        if (File.Exists(filePath)) 
        {
            File.Delete(filePath);
        }
        
        // Create the file.
        using (FileStream fs = File.Create(filePath)) 
        {
            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.Open(filePath, 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());
            }
        }
    }
}

import System.*;
import System.IO.*;
import System.Text.*;

class Test
{
    public static void main(String[] args)
    {
        String path = "c:\\temp\\MyTest.txt";

        // Delete the file if it exists.
        if (!(File.Exists(path))) {
            // Create the file.
            FileStream fs = File.Create(path);
            try {
                ubyte info[] = (new UTF8Encoding(true)).GetBytes("This is " 
                    + " some text in the file.");

                // Add some information to the file.
                fs.Write(info, 0, info.length);
            }
            finally {
                fs.Dispose();
            }
        }

        // Open the stream and read it back.
        FileStream fs = File.Open(path, FileMode.Open, FileAccess.Read);
        try {
            ubyte b[] = new ubyte[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 (System.Exception e) {
                Console.WriteLine("Writing was disallowed, as expected: {0}",
                    e.ToString());
            }
        }
        finally {
            fs.Dispose();
        }
    } //main
} //Test

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

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