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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
)

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.

access
Type: System.IO.FileAccess

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

Return Value

Type: System.IO.FileStream

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

Exception Condition
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 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 and access is not Read.

-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 or access 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.

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());
            }
        }
    }
}

FileIOPermission

for reading from and writing to the specified file. Associated enumerations: FileIOPermissionAccess.Read, FileIOPermissionAccess.Write

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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