BeginRead Method

BufferedStream.BeginRead Method (Byte[], Int32, Int32, AsyncCallback, Object)

.NET Framework 4.6 and 4.5

Begins an asynchronous read operation. (Consider using ReadAsync instead; see the Remarks section.)

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

public override IAsyncResult BeginRead(
	byte[] buffer,
	int offset,
	int count,
	AsyncCallback callback,
	object state


Type: System.Byte[]

The buffer to read the data into.

Type: System.Int32

The byte offset in buffer at which to begin writing data read from the stream.

Type: System.Int32

The maximum number of bytes to read.

Type: System.AsyncCallback

An optional asynchronous callback, to be called when the read is complete.

Type: System.Object

A user-provided object that distinguishes this particular asynchronous read request from other requests.

Return Value

Type: System.IAsyncResult

An object that represents the asynchronous read, which could still be pending.

Exception Condition

buffer is null.


offset or count is negative.


Attempted an asynchronous read past the end of the stream.


The buffer length minus offset is less than count.


The current stream does not support the read operation.

In the .NET Framework 4 and earlier versions, you have to use methods such as BeginRead and EndRead to implement asynchronous file operations. These methods are still available in the .NET Framework 4.5 to support legacy code; however, the new async methods, such as ReadAsync, WriteAsync, and FlushAsync, help you implement asynchronous file operations more easily.

EndWrite must be called exactly once for every call to BeginRead. Failing to end a read process before beginning another read can cause undesirable behavior such as deadlock.


Use the CanRead property to determine whether the current instance supports reading.

EndRead must be called with this IAsyncResult to find out how many bytes were read.

.NET Framework
Available since 4.5
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