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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
)

Parameters

path
Type: System.String

The file to open.

mode
Type: System.IO.FileMode

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

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

ExceptionCondition
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).

IOException

An I/O error occurred while opening the file.

UnauthorizedAccessException

path specified a file that is read-only.

-or-

This operation is not supported on the current platform.

-or-

path specified a directory.

-or-

The caller does not have the required permission.

-or-

mode is Create and the specified file is a hidden file.

ArgumentOutOfRangeException

mode specified an invalid value.

FileNotFoundException

The file specified in path was not found.

NotSupportedException

path is in an invalid format.

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 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) 
            {
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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