OpenWrite Method

File.OpenWrite Method (String)


Opens an existing file or creates a new file for writing.

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

public static FileStream OpenWrite(
	string path


Type: System.String

The file to be opened for writing.

Return Value

Type: System.IO.FileStream

An unshared FileStream object on the specified path with Write access.

Exception Condition

The caller does not have the required permission.


path specified a read-only file or directory.


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


path is null.


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).


path is in an invalid format.

This method is equivalent to the FileStream(String, FileMode, FileAccess, FileShare) constructor overload with file mode set to OpenOrCreate, the access set to Write, and the share mode set to None.

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 (such as “Second run”), the file will contain a mix of the strings (“Second runtest of the OpenWrite method”).

The path parameter may specify relative or absolute path information. Relative path information is interpreted as relative to the current working directory. To obtain the current working directory, use the GetCurrentDirectory method.

For a list of common I/O tasks, see Common I/O Tasks.

The following example opens a file for reading and writing.

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

class Test 
    public static void Main() 
        string path = @"c:\temp\MyTest.txt";

        // Open the stream and write to it.
        using (FileStream fs = File.OpenWrite(path)) 
            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 = File.OpenRead(path)) 
            byte[] b = new byte[1024];
            UTF8Encoding temp = new UTF8Encoding(true);

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


for writing to the specified file. Associated enumeration: FileIOPermissionAccess.Write

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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