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Stream.BeginWrite Method

Begins an asynchronous write operation.

[Visual Basic]
Public Overridable Function BeginWrite( _
   ByVal buffer() As Byte, _
   ByVal offset As Integer, _
   ByVal count As Integer, _
   ByVal callback As AsyncCallback, _
   ByVal state As Object _
) As IAsyncResult
public virtual IAsyncResult BeginWrite(
 byte[] buffer,
 int offset,
 int count,
 AsyncCallback callback,
 object state
public: virtual IAsyncResult* BeginWrite(
 unsigned char buffer __gc[],
 int offset,
 int count,
 AsyncCallback* callback,
 Object* state
public function BeginWrite(
   buffer : Byte[],
 offset : int,
 count : int,
 callback : AsyncCallback,
 state : Object
) : IAsyncResult;


The buffer to write data from.
The byte offset in buffer from which to begin writing.
The maximum number of bytes to write.
An optional asynchronous callback, to be called when the write is complete.
A user-provided object that distinguishes this particular asynchronous write request from other requests.

Return Value

An IAsyncResult that represents the asynchronous write, which could still be pending.


Exception Type Condition
IOException Attempted an asynchronous write past the end of the stream, or a disk error occurs.
ArgumentException One or more or the arguments is invalid.
ObjectDisposedException Methods were called after the stream was closed.
NotSupportedException The current Stream implementation does not support the write operation.


For an example of creating a file and writing text to a file, see Writing Text to a File. For an example of reading text from a file, see Reading Text from a File. For an example of reading from and writing to a binary file, see Reading and Writing to a Newly Created Data File. For an example of asynchronous file I/O, see Asynchronous File I/O.

The default implementation of BeginWrite on a stream calls the Write method synchronously, which means that Write might block on some streams. However, instances of classes such as FileStream and NetworkStream fully support asynchronous operations if the instances have been opened asynchronously. Therefore, calls to BeginWrite will not block on those streams. You can override BeginWrite (by using async delegates, for example) to provide asynchronous behavior.

Pass the IAsyncResult returned by the current method to EndWrite to ensure that the write completes and frees resources appropriately. You can do this either by using the same code that called BeginWrite or in a callback passed to BeginWrite. If an error occurs during an asynchronous write, an exception will not be thrown until EndWrite is called with the IAsyncResult returned by this method.

If a stream is writable, writing at the end of the stream expands the stream.

The current position in the stream is updated when you issue the asynchronous read or write, not when the I/O operation completes. Multiple simultaneous asynchronous requests render the request completion order uncertain.

Use the CanWrite property to determine whether the current instance supports writing.

If a stream is closed or you pass an invalid argument, exceptions are thrown immediately from BeginWrite. Errors that occur during an asynchronous write request, such as a disk failure during the I/O request, occur on the threadpool thread and throw exceptions when calling EndWrite.


Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

Stream Class | Stream Members | System.IO Namespace | EndWrite | CanWrite | Working with I/O | Reading Text from a File | Writing Text to a File | Asynchronous File I/O

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