Stream.Read Method (System.IO)

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.NET Framework Class Library

Stream.Read Method

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When overridden in a derived class, reads a sequence of bytes from the current stream and advances the position within the stream by the number of bytes read.

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

Syntax

Visual Basic


Public MustOverride Function Read ( _
	<OutAttribute> buffer As Byte(), _
	offset As Integer, _
	count As Integer _
) As Integer


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

Visual C++


public:
virtual int Read(
	[InAttribute] [OutAttribute] array<unsigned char>^ buffer, 
	int offset, 
	int count
) abstract


abstract Read : 
        buffer:byte[] byref * 
        offset:int * 
        count:int -> int

Parameters

buffer: Type: System.Byte[]
An array of bytes. When this method returns, the buffer contains the specified byte array with the values between offset and (offset + count - 1) replaced by the bytes read from the current source.

offset: Type: System.Int32
The zero-based byte offset in buffer at which to begin storing the data read from the current stream.

count: Type: System.Int32
The maximum number of bytes to be read from the current stream.

Return Value

Type: System.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

Exception	Condition
ArgumentException	The sum of offset and count is larger than the buffer length.
ArgumentNullException	buffer is null.
ArgumentOutOfRangeException	offset or count is negative.
IOException	An I/O error occurs.
NotSupportedException	The stream does not support reading.
ObjectDisposedException	Methods were called after the stream was closed.

Remarks

Use the CanRead property to determine whether the current instance supports reading. Use the ReadAsync method to read asynchronously from the current stream.

Implementations of this method read a maximum of count bytes from the current stream and store them in buffer beginning at offset. The current position within the stream is advanced by the number of bytes read; however, if an exception occurs, the current position within the stream remains unchanged. Implementations return the number of bytes read. The implementation will block until at least one byte of data can be read, in the event that no data is available. Read returns 0 only when there is no more data in the stream and no more is expected (such as a closed socket or end of file). An implementation is free to return fewer bytes than requested even if the end of the stream has not been reached.

Use BinaryReader for reading primitive data types.

Examples

The following example shows how to use Read to read a block of data.

Visual Basic


Imports System
Imports System.IO

Public Class Block
    Public Shared Sub Main()
        Dim s As Stream = New MemoryStream()
        For i As Integer = 0 To 99
            s.WriteByte(CType(i, Byte))
        Next i
        s.Position = 0

        ' Now read s into a byte buffer.
        Dim bytes(s.Length) As Byte
        Dim numBytesToRead As Integer = s.Length
        Dim numBytesRead As Integer = 0
        Dim n As Integer
        While numBytesToRead > 0
            ' Read may return anything from 0 to 10.
            n = s.Read(bytes, numBytesRead, 10)
            ' The end of the file is reached.
            If n = 0 Then
                Exit While
            End If
            numBytesRead += n
            numBytesToRead -= n
        End While
        s.Close()
        ' numBytesToRead should be 0 now, and numBytesRead should
        ' equal 100.
        Console.WriteLine("number of bytes read: {0:d}", numBytesRead)
    End Sub
End Class


using System;
using System.IO;

public class Block
{
    public static void Main()
    {
        Stream s = new MemoryStream();
        for (int i = 0; i < 100; i++)
        {
            s.WriteByte((byte)i);
        }
        s.Position = 0;

        // Now read s into a byte buffer.
        byte[] bytes = new byte[s.Length];
        int numBytesToRead = (int) s.Length;
        int numBytesRead = 0;
        while (numBytesToRead > 0)
        {
            // Read may return anything from 0 to 10.
            int n = s.Read(bytes, numBytesRead, 10);
            // The end of the file is reached.
            if (n == 0)
            {
                break;
            }
            numBytesRead += n;
            numBytesToRead -= n;
        }
        s.Close();
        // numBytesToRead should be 0 now, and numBytesRead should
        // equal 100.
        Console.WriteLine("number of bytes read: {0:d}", numBytesRead);
    }
}

Visual C++


using namespace System;
using namespace System::IO;

public ref class Block
{
public:
    static void Main()
    {
        Stream^ s = gcnew MemoryStream();
        for (int i = 0; i < 100; i++)
        {
            s->WriteByte((Byte)i);
        }
        s->Position = 0;

        // Now read s into a byte buffer.
        array<Byte>^ bytes = gcnew array<Byte>(s->Length);
        int numBytesToRead = (int) s->Length;
        int numBytesRead = 0;
        while (numBytesToRead > 0)
        {
            // Read may return anything from 0 to 10.
            int n = s->Read(bytes, numBytesRead, 10);
            // The end of the file is reached.
            if (n == 0)
            {
                break;
            }
            numBytesRead += n;
            numBytesToRead -= n;
        }
        s->Close();
        // numBytesToRead should be 0 now, and numBytesRead should
        // equal 100.
        Console::WriteLine("number of bytes read: {0:d}", numBytesRead);
    }
};

int main()
{
    Block::Main();
}

Version Information

.NET Framework

Supported in: 4.5, 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

Platforms

Windows 8 Release Preview, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 SP2, 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.

Reference

Stream Class

System.IO Namespace

Other Resources

File and Stream I/O

How to: Read Text from a File

How to: Write Text to a File