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Buffer.BlockCopy Method

Copies a specified number of bytes from a source array starting at a particular offset to a destination array starting at a particular offset.

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

'Declaration
Public Shared Sub BlockCopy ( _
	src As Array, _
	srcOffset As Integer, _
	dst As Array, _
	dstOffset As Integer, _
	count As Integer _
)

Parameters

src
Type: System.Array

The source buffer.

srcOffset
Type: System.Int32

The zero-based byte offset into src.

dst
Type: System.Array

The destination buffer.

dstOffset
Type: System.Int32

The zero-based byte offset into dst.

count
Type: System.Int32

The number of bytes to copy.

ExceptionCondition
ArgumentNullException

src or dst is Nothing.

ArgumentException

src or dst is not an array of primitives.

-or-

The number of bytes in src is less than srcOffset plus count.

-or-

The number of bytes in dst is less than dstOffset plus count.

ArgumentOutOfRangeException

srcOffset, dstOffset, or count is less than 0.

This method copies count bytes from src, beginning at srcOffset, to dst, beginning at dstOffset. Both srcOffset and dstOffset are zero-based; that is, the first byte in each buffer is at position 0, not position 1.

The BlockCopy method accesses the bytes in the src parameter array using offsets into memory, not programming constructs such as indexes or upper and lower array bounds. For example, if in the programming language of your application you declare an Int32 array with a zero-based lower bound of -50, and then pass the array and an offset of 5 to the BlockCopy method, the first array element the method will access is the second element of the array, which is at index -49. Furthermore, which byte of array element -49 is accessed first depends on the endianness of the computer that is executing your application.

As its name suggests, the BlockCopy method copies a block of bytes as a whole, rather than copying one byte at a time. Therefore, if src and dst reference the same array, and the range from srcOffset + count -1 overlaps the range from dstOffset + count - 1, the values of the overlapping bytes are not overwritten before they are copied to the destination. In the following example, the values of bytes 0-16 in an array named arr are copied to bytes 12-28. Despite the overlapping range, the values of the source bytes are successfully copied.

Const INT_SIZE As Integer = 4
Dim arr() As Integer = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 }
Buffer.BlockCopy(arr, 0 * INT_SIZE, arr, 3 * INT_SIZE, 4 * INT_SIZE)
For Each value As Integer In arr
   Console.Write("{0}  ", value)
Next 
' The example displays the following output: 
'       2  4  6  2  4  6  8  16  18  20      

In the following example, the values of bytes 12-28 in an array named arr are copied to bytes 0-16. Again, despite the overlapping range, the values of the source bytes are successfully copied.

Const INT_SIZE As Integer = 4
Dim arr() As Integer = { 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 }
Buffer.BlockCopy(arr, 3 * INT_SIZE, arr, 0 * INT_SIZE, 4 * INT_SIZE)
For Each value As Integer In arr
   Console.Write("{0}  ", value)
Next 
' The example displays the following output: 
'       8  10  12  14  10  12  14  16  18  20      

The following example copies regions of arrays by using the BlockCopy method. For each BlockCopy operation, it lists the source and destination arrays as both an array of values and as a sequence of bytes. The example illustrates the importance of considering a system's endianness when working with the BlockCopy method: Because Windows systems are little-endian, the lower-order bytes of a primitive data type's value precede the higher-order bytes.

Module Example
    ' Display the individual bytes in the array in hexadecimal. 
    Sub DisplayArray(arr As Array, name As String)
        Console.Write("{0,11}:", name)
        For ctr As Integer = 0 to arr.Length - 1
            Dim bytes() As Byte = BitConverter.GetBytes(arr(ctr))
            For Each byteValue As Byte In bytes
               Console.Write(" {0:X2}", byteValue)
            Next 
        Next
        Console.WriteLine()
    End Sub 

    ' Display the individual array element values in hexadecimal. 
    Sub DisplayArrayValues(arr As Array, name As String)
       ' Get the length of one element in the array. 
       Dim elementLength As Integer = Buffer.ByteLength(arr) / arr.Length
       Dim formatString As String = String.Format(" {{0:X{0}}}", 2 * elementLength)
       Console.Write("{0,11}:", name)
       For ctr As Integer = 0 to arr.Length - 1
         Console.Write(formatString, arr(ctr))
       Next
       Console.WriteLine()  
    End Sub 

    Sub Main()
       Console.WindowWidth = 120
        ' These are source and destination arrays for BlockCopy. 
        Dim src()  As Short = { 258, 259, 260, 261, 262, 263, 264, _
                                 265, 266, 267, 268, 269, 270 }
        Dim dest() As Long = { 17, 18, 19, 20 }

        ' Display the initial value of the arrays in memory.
        Console.WriteLine( "Initial values of arrays:")
        Console.WriteLine("   Array values as Bytes:") 
        DisplayArray(src, "src" )
        DisplayArray(dest, "dest" )
        Console.WriteLine("   Array values:")
        DisplayArrayValues(src, "src")
        DisplayArrayValues(dest, "dest")
        Console.WriteLine()

        ' Copy bytes 5-10 from source to index 7 in destination and display the result.
        Buffer.BlockCopy( src, 5, dest, 7, 6 )
        Console.WriteLine("Buffer.BlockCopy(src, 5, dest, 7, 6 )")
        Console.WriteLine("   Array values as Bytes:")
        DisplayArray(src, "src")
        DisplayArray(dest, "dest")
        Console.WriteLine("   Array values:")
        DisplayArrayValues(src, "src")
        DisplayArrayValues(dest, "dest")
        Console.WriteLine()

        ' Copy bytes 16-20 from source to index 22 in destination and display the result. 
        Buffer.BlockCopy( src, 16, dest, 22, 5 )
        Console.WriteLine("Buffer.BlockCopy(src, 16, dest, 22, 5)")
        Console.WriteLine("   Array values as Bytes:")
        DisplayArray(src, "src")
        DisplayArray(dest, "dest")
        Console.WriteLine("   Array values:")
        DisplayArrayValues(src, "src")
        DisplayArrayValues(dest, "dest")
        Console.WriteLine()

        ' Copy overlapping range of bytes 4-10 to index 5 in source.
        Buffer.BlockCopy( src, 4, src, 5, 7 )
        Console.WriteLine("Buffer.BlockCopy( src, 4, src, 5, 7)")
        Console.WriteLine("   Array values as Bytes:")
        DisplayArray(src, "src")
        DisplayArray(dest, "dest")
        Console.WriteLine("   Array values:")
        DisplayArrayValues(src, "src")
        DisplayArrayValues(dest, "dest")
        Console.WriteLine()

        ' Copy overlapping range of bytes 16-22 to index 15 in source. 
        Buffer.BlockCopy(src, 16, src, 15, 7)
        Console.WriteLine("Buffer.BlockCopy( src, 16, src, 15, 7)")
        Console.WriteLine("   Array values as Bytes:")
        DisplayArray(src, "src")
        DisplayArray(dest, "dest")
        Console.WriteLine("   Array values:")
        DisplayArrayValues(src, "src")
        DisplayArrayValues(dest, "dest")
    End Sub  
End Module  
' This example displays the following output: 
'    Initial values of arrays: 
'       Array values as Bytes: 
'            src: 02 01 03 01 04 01 05 01 06 01 07 01 08 01 09 01 0A 01 0B 01 0C 01 0D 01 0E 01 
'           dest: 11 00 00 00 00 00 00 00 12 00 00 00 00 00 00 00 13 00 00 00 00 00 00 00 14 00 00 00 00 00 00 00 
'       Array values: 
'            src: 0102 0103 0104 0105 0106 0107 0108 0109 010A 010B 010C 010D 010E 
'           dest: 0000000000000011 0000000000000012 0000000000000013 0000000000000014 
'     
'    Buffer.BlockCopy(src, 5, dest, 7, 6 ) 
'       Array values as Bytes: 
'            src: 02 01 03 01 04 01 05 01 06 01 07 01 08 01 09 01 0A 01 0B 01 0C 01 0D 01 0E 01 
'           dest: 11 00 00 00 00 00 00 01 05 01 06 01 07 00 00 00 13 00 00 00 00 00 00 00 14 00 00 00 00 00 00 00 
'       Array values: 
'            src: 0102 0103 0104 0105 0106 0107 0108 0109 010A 010B 010C 010D 010E 
'           dest: 0100000000000011 0000000701060105 0000000000000013 0000000000000014 
'     
'    Buffer.BlockCopy(src, 16, dest, 22, 5) 
'       Array values as Bytes: 
'            src: 02 01 03 01 04 01 05 01 06 01 07 01 08 01 09 01 0A 01 0B 01 0C 01 0D 01 0E 01 
'           dest: 11 00 00 00 00 00 00 01 05 01 06 01 07 00 00 00 13 00 00 00 00 00 0A 01 0B 01 0C 00 00 00 00 00 
'       Array values: 
'            src: 0102 0103 0104 0105 0106 0107 0108 0109 010A 010B 010C 010D 010E 
'           dest: 0100000000000011 0000000701060105 010A000000000013 00000000000C010B 
'     
'    Buffer.BlockCopy( src, 4, src, 5, 7) 
'       Array values as Bytes: 
'            src: 02 01 03 01 04 04 01 05 01 06 01 07 08 01 09 01 0A 01 0B 01 0C 01 0D 01 0E 01 
'           dest: 11 00 00 00 00 00 00 01 05 01 06 01 07 00 00 00 13 00 00 00 00 00 0A 01 0B 01 0C 00 00 00 00 00 
'       Array values: 
'            src: 0102 0103 0404 0501 0601 0701 0108 0109 010A 010B 010C 010D 010E 
'           dest: 0100000000000011 0000000701060105 010A000000000013 00000000000C010B 
'     
'    Buffer.BlockCopy( src, 16, src, 15, 7) 
'       Array values as Bytes: 
'            src: 02 01 03 01 04 04 01 05 01 06 01 07 08 01 09 0A 01 0B 01 0C 01 0D 0D 01 0E 01 
'           dest: 11 00 00 00 00 00 00 01 05 01 06 01 07 00 00 00 13 00 00 00 00 00 0A 01 0B 01 0C 00 00 00 00 00 
'       Array values: 
'            src: 0102 0103 0404 0501 0601 0701 0108 0A09 0B01 0C01 0D01 010D 010E 
'           dest: 0100000000000011 0000000701060105 010A000000000013 00000000000C010B

.NET Framework

Supported in: 4.5.2, 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

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.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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