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StreamReader Constructor (Stream, Encoding, Boolean, Int32)

Initializes a new instance of the StreamReader class for the specified stream, with the specified character encoding, byte order mark detection option, and buffer size.

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

new : 
        stream:Stream * 
        encoding:Encoding * 
        detectEncodingFromByteOrderMarks:bool * 
        bufferSize:int -> StreamReader


Type: System.IO.Stream
The stream to be read.
Type: System.Text.Encoding
The character encoding to use.
Type: System.Boolean
Indicates whether to look for byte order marks at the beginning of the file.
Type: System.Int32
The minimum buffer size.


The stream does not support reading.


stream or encoding is a null reference (Nothing in Visual Basic).


bufferSize is less than or equal to zero.

The buffer size, in number of 16-bit characters, is set by the bufferSize parameter. If bufferSize is less than the minimum allowable size (128 characters), the minimum allowable size is used.

This constructor allows you to change the encoding the first time you read from the StreamReader object. The detectEncodingFromByteOrderMarks parameter detects the encoding by looking at the first three bytes of the stream. It automatically recognizes UTF-8, little-endian Unicode, and big-endian Unicode text if the file starts with the appropriate byte order marks. Otherwise, the user-provided encoding is used. See the Encoding.GetPreamble method for more information.

The StreamReader object calls Dispose on the provided Stream object when StreamReader.Dispose is called.


When reading from a Stream, it is more efficient to use a buffer that is the same size as the internal buffer of the stream.

Caution noteCaution

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 code example demonstrates this StreamReader constructor.

No code example is currently available or this language may not be supported.

.NET Framework

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

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

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