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File.Open Method (String, FileMode)

Opens a FileStream on the specified path with read/write access.

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

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



The file to open.


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.

Return Value

A FileStream opened in the specified mode and path, with read/write access and not shared.

Exception typeCondition


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


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


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.


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


An I/O error occurred while opening the file.


path specified a file that is read-only.


This operation is not supported on the current platform.


path specified a directory.


The caller does not have the required permission.


mode specified an invalid value.


The file specified in path was not found.


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



Rename or move a file.



Copy a file.



Get the size of a file.


Get the attributes of a file.


Set the attributes of a file.


Determine if a 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.



The following code example creates a temporary file and writes some text to it. The example then opens the file, using T:System.IO.FileMode.Open; that is, if the file did not already exist, it would not be created.

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

class Test 
    public static void Main() 
        // Create a temporary file, and put some data into it.
        string path = Path.GetTempFileName();
        using (FileStream fs = File.Open(path, FileMode.Open, FileAccess.Write, FileShare.None)) 
            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(path, FileMode.Open)) 
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b,0,b.Length) > 0) 

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 {
        // Open the stream and read it back.
        FileStream fs = File.Open(path, FileMode.Open);

        try {
            ubyte b[] = new ubyte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b, 0, b.length) > 0) {
        finally {
    } //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

Community Additions

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