StreamWriter Constructor (String, Boolean, Encoding, Int32)


Initializes a new instance of the StreamWriter class for the specified file on the specified path, using the specified encoding and buffer size. If the file exists, it can be either overwritten or appended to. If the file does not exist, this constructor creates a new file.

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

public StreamWriter(
	string path,
	bool append,
	Encoding encoding,
	int bufferSize


Type: System.String

The complete file path to write to.

Type: System.Boolean

true to append data to the file; false to overwrite the file. If the specified file does not exist, this parameter has no effect, and the constructor creates a new file.

Type: System.Text.Encoding

The character encoding to use.

Type: System.Int32

The buffer size, in bytes.

Exception Condition

path is an empty string ("").


path contains the name of a system device (com1, com2, and so on).


path or encoding is null.


bufferSize is negative.


path includes an incorrect or invalid syntax for file name, directory name, or volume label syntax.


The caller does not have the required permission.


Access is denied.


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


The specified path, file name, or both exceed the system-defined maximum length. For example, on Windows-based platforms, paths must not exceed 248 characters, and file names must not exceed 260 characters.

This constructor initializes the Encoding property using the encoding parameter. For additional information, see Encoding.

path can be a file name, including a file on a Universal Naming Convention (UNC) share.

path is not required to be a file stored on disk; it can be any part of a system that supports access via streams.


When you compile a set of characters with a particular cultural setting and retrieve those same characters with a different cultural setting, the characters might not be interpretable, and could cause an exception to be thrown.

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

The following example demonstrates this constructor.

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

namespace ConsoleApplication
    class Program
        static void Main(string[] args)
            string fileName = "test.txt";
            string textToAdd = "Example text in file";

            using (StreamWriter writer = new StreamWriter(fileName, true, Encoding.UTF8, 512))


for reading and writing files. Associated enumeration: FileIOPermissionAccess.Read, FileIOPermissionAccess.Write

.NET Framework
Available since 1.1
Available since 2.0
Windows Phone Silverlight
Available since 7.0
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