FileInfo.OpenWrite Method

Definition

Namespace:

System.IO

Assemblies:

netstandard.dll, System.Runtime.dll

Source:

FileInfo.cs

Creates a write-only FileStream.

C#

public System.IO.FileStream OpenWrite();

Returns

FileStream

A write-only unshared FileStream object for a new or existing file.

Exceptions

UnauthorizedAccessException

The path specified when creating an instance of the FileInfo object is read-only or is a directory.

DirectoryNotFoundException

The path specified when creating an instance of the FileInfo object is invalid, such as being on an unmapped drive.

Examples

The following example opens a file for writing and then reads from the file.

C#

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

class Test
{
    public static void Main()
    {
        string path = @"c:\Temp\MyTest.txt";
        FileInfo fi = new FileInfo(path);

        // Open the stream for writing.
        using (FileStream fs = fi.OpenWrite())
        {
            Byte[] info =
                new UTF8Encoding(true).GetBytes("This is to test the OpenWrite method.");

            // Add some information to the file.
            fs.Write(info, 0, info.Length);
        }

        // Open the stream and read it back.
        using (FileStream fs = fi.OpenRead())
        {
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

            while (fs.Read(b,0,b.Length) > 0)
            {
                Console.WriteLine(temp.GetString(b));
            }
        }
    }
}
//This code produces output similar to the following;
//This is to test the OpenWrite method.

Remarks

The OpenWrite method opens a file if one already exists for the file path, or creates a new file if one does not exist. For an existing file, it does not append the new text to the existing text. Instead, it overwrites the existing characters with the new characters. If you overwrite a longer string (such as "This is a test of the OpenWrite method") with a shorter string (like "Second run"), the file will contain a mix of the strings ("Second run test of the OpenWrite method.").

Applies to