UnmanagedMemoryStream.Read Method

Definition

Namespace:

System.IO

Assembly:

System.Runtime.dll

Overloads

Read(Span<Byte>)	Reads all the bytes of this unmanaged memory stream into the specified span of bytes.
Read(Byte[], Int32, Int32)	Reads the specified number of bytes into the specified array.

Read(Span<Byte>)

Source:

UnmanagedMemoryStream.cs

Reads all the bytes of this unmanaged memory stream into the specified span of bytes.

public:
 override int Read(Span<System::Byte> buffer);

public override int Read (Span<byte> buffer);

override this.Read : Span<byte> -> int

Public Overrides Function Read (buffer As Span(Of Byte)) As Integer

Parameters

buffer

Span<Byte>

When this method returns, this span contains all the bytes from the unmanaged memory stream.

Returns

Int32

The total number of bytes read into the destination.

Read(Byte[], Int32, Int32)

Source:

UnmanagedMemoryStream.cs

Reads the specified number of bytes into the specified array.

public:
 override int Read(cli::array <System::Byte> ^ buffer, int offset, int count);

public override int Read (byte[] buffer, int offset, int count);

override this.Read : byte[] * int * int -> int

Public Overrides Function Read (buffer As Byte(), offset As Integer, count As Integer) As Integer

Parameters

buffer

Byte[]

When this method returns, contains the specified byte array with the values between offset and (offset + count - 1) replaced by the bytes read from the current source. This parameter is passed uninitialized.

offset

Int32

The zero-based byte offset in buffer at which to begin storing the data read from the current stream.

count

Int32

The maximum number of bytes to read from the current stream.

Returns

Int32

The total number of bytes read into the buffer. This can be less than the number of bytes requested if that many bytes are not currently available, or zero (0) if the end of the stream has been reached.

Exceptions

ObjectDisposedException

The stream is closed.

NotSupportedException

The underlying memory does not support reading.

-or-

The CanRead property is set to false.

ArgumentNullException

The buffer parameter is set to null.

ArgumentOutOfRangeException

The offset parameter is less than zero.

-or-

The count parameter is less than zero.

ArgumentException

The length of the buffer array minus the offset parameter is less than the count parameter.

Examples

The following code example demonstrates how to read from and write to unmanaged memory using the UnmanagedMemoryStream class. A block of unmanaged memory is allocated and de-allocated using the Marshal class.

// Note: you must compile this sample using the unsafe flag.
// From the command line, type the following: csc sample.cs /unsafe

using System;
using System.IO;
using System.Text;
using System.Runtime.InteropServices;

unsafe class TestWriter
{
    static void Main()
    {
        // Create some data to read and write.
        byte[] message = UnicodeEncoding.Unicode.GetBytes("Here is some data.");

        // Allocate a block of unmanaged memory and return an IntPtr object.	
        IntPtr memIntPtr = Marshal.AllocHGlobal(message.Length);

        // Get a byte pointer from the IntPtr object.
        byte* memBytePtr = (byte*)memIntPtr.ToPointer();

        // Create an UnmanagedMemoryStream object using a pointer to unmanaged memory.
        UnmanagedMemoryStream writeStream = new UnmanagedMemoryStream(memBytePtr, message.Length, message.Length, FileAccess.Write);

        // Write the data.
        writeStream.Write(message, 0, message.Length);

        // Close the stream.
        writeStream.Close();

        // Create another UnmanagedMemoryStream object using a pointer to unmanaged memory.
        UnmanagedMemoryStream readStream = new UnmanagedMemoryStream(memBytePtr, message.Length, message.Length, FileAccess.Read);

        // Create a byte array to hold data from unmanaged memory.
        byte[] outMessage = new byte[message.Length];

        // Read from unmanaged memory to the byte array.
        readStream.Read(outMessage, 0, message.Length);

        // Close the stream.
        readStream.Close();

        // Display the data to the console.
        Console.WriteLine(UnicodeEncoding.Unicode.GetString(outMessage));

        // Free the block of unmanaged memory.
        Marshal.FreeHGlobal(memIntPtr);

        Console.ReadLine();
    }
}

Remarks

The offset parameter gives the offset of the byte in the array parameter (the buffer index) at which to begin reading, and the count parameter gives the maximum number of bytes to be read from this stream. The returned value is the actual number of bytes read, or zero if the end of the stream is reached. If the read operation is successful, the current position of the stream is advanced by the number of bytes read. If an exception occurs, the current position of the stream is unchanged.

The Read method returns zero only after reaching the end of the stream. Otherwise, Read always reads at least one byte from the stream before returning. If no data is available from the stream upon a call to Read, the method will block until at least one byte of data can be returned. An implementation is free to return fewer bytes than requested even if the end of the stream has not been reached.