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Marshal.Copy Method (IntPtr, Char(), Int32, Int32)

Updated: March 2011

Copies data from an unmanaged memory pointer to a managed character array.

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

'Declaration
Public Shared Sub Copy ( _
	source As IntPtr, _
	destination As Char(), _
	startIndex As Integer, _
	length As Integer _
)

Parameters

source
Type: System.IntPtr
The memory pointer to copy from.
destination
Type: System.Char()
The array to copy to.
startIndex
Type: System.Int32
The zero-based index in the destination array where copying should start.
length
Type: System.Int32
The number of array elements to copy.

ExceptionCondition
ArgumentNullException

source, destination, startIndex, or length is Nothing.

Unmanaged, C-style arrays do not contain bounds information, which prevents the startIndex and length parameters from being validated. Thus, the unmanaged data corresponding to the source parameter populates the managed array regardless of its usefulness. You must initialize the managed array with the appropriate size before calling this method.

The following example copies an array to unmanaged memory and then copies the unmanaged array back to managed memory.


' Remember that the actual size of System.Char in unmanaged memory is 2.

Imports System
Imports System.Runtime.InteropServices



Module Module1

    Sub Main()
        ' Create a managed array.
        Dim managedArray As Char() = New Char(999) {}
        managedArray(0) = "a"c
        managedArray(1) = "b"c
        managedArray(2) = "c"c
        managedArray(3) = "d"c
        managedArray(999) = "Z"c

        ' Initialize unmanged memory to hold the array.
        ' Dim size As Integer = Marshal.SizeOf(managedArray[0]) * managedArray.Length;  ' Incorrect
        Dim size As Integer = Marshal.SystemDefaultCharSize * managedArray.Length       ' Correct

        Dim pnt As IntPtr = Marshal.AllocHGlobal(size)

        Try
            ' Copy the array to unmanaged memory.
            Marshal.Copy(managedArray, 0, pnt, managedArray.Length)

            ' Copy the unmanaged array back to another managed array.

            Dim managedArray2 As Char() = New Char(managedArray.Length - 1) {}

            Marshal.Copy(pnt, managedArray2, 0, managedArray.Length)
            Console.WriteLine("Here is the roundtripped array: {0} {1} {2} {3} {4}", managedArray2(0), managedArray2(1), managedArray2(2), managedArray2(3), managedArray2(999))


            Console.WriteLine("The array was coppied to unmanaged memory and back.")
        Finally
            ' Free the unmanaged memory.
            Marshal.FreeHGlobal(pnt)

        End Try
    End Sub
End Module


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

  • SecurityCriticalAttribute 

    requires full trust for the immediate caller. This member cannot be used by partially trusted or transparent code.

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Date

History

Reason

March 2011

Corrected the description of the startIndex parameter.

Content bug fix.

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