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FileStream::WriteByte Method

Writes a byte to the current position in the file stream.

Namespace:  System.IO
Assembly:  mscorlib (in mscorlib.dll)
virtual void WriteByte(
	unsigned char value
) override


Type: System::Byte

A byte to write to the stream.


The stream is closed.


The stream does not support writing.

This method overrides WriteByte.

Use WriteByte to write a byte to a FileStream efficiently. If the stream is closed or not writable, an exception will be thrown.


Use the CanWrite property to determine whether the current instance supports writing. For additional information, see CanWrite.

Notes to Implementers

The default implementation on Stream creates a new single-byte array and then calls Write. While this is formally correct, it is inefficient. Any stream with an internal buffer should override this method and provide a much more efficient version that reads the buffer directly, avoiding the extra array allocation on every call.

For a list of common file and directory operations, see Common I/O Tasks.

The following code example shows how to write data to a file, byte by byte, and then verify that the data was written correctly.

using namespace System;
using namespace System::IO;
int main()
   String^ fileName =  "Test@##@.dat";

   // Create random data to write to the file. 
   array<Byte>^dataArray = gcnew array<Byte>(100000);
   (gcnew Random)->NextBytes( dataArray );
   FileStream^ fileStream = gcnew FileStream( fileName,FileMode::Create );

      // Write the data to the file, byte by byte. 
      for ( int i = 0; i < dataArray->Length; i++ )
         fileStream->WriteByte( dataArray[ i ] );


      // Set the stream position to the beginning of the file.
      fileStream->Seek( 0, SeekOrigin::Begin );

      // Read and verify the data. 
      for ( int i = 0; i < fileStream->Length; i++ )
         if ( dataArray[ i ] != fileStream->ReadByte() )
            Console::WriteLine( "Error writing data." );
            return  -1;

      Console::WriteLine( "The data was written to {0} " 
      "and verified.", fileStream->Name );


.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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