Marshal.StructureToPtr Method

Definition

Namespace:

System.Runtime.InteropServices

Assembly:

System.Runtime.InteropServices.dll

Overloads

StructureToPtr(Object, IntPtr, Boolean)	Marshals data from a managed object to an unmanaged block of memory.
StructureToPtr<T>(T, IntPtr, Boolean)	Marshals data from a managed object of a specified type to an unmanaged block of memory.

StructureToPtr(Object, IntPtr, Boolean)

Source:

Marshal.cs

Marshals data from a managed object to an unmanaged block of memory.

public:
 static void StructureToPtr(System::Object ^ structure, IntPtr ptr, bool fDeleteOld);

public static void StructureToPtr (object structure, IntPtr ptr, bool fDeleteOld);

static member StructureToPtr : obj * nativeint * bool -> unit

Public Shared Sub StructureToPtr (structure As Object, ptr As IntPtr, fDeleteOld As Boolean)

Parameters

structure

Object

A managed object that holds the data to be marshaled. This object must be a structure or an instance of a formatted class.

ptr

IntPtr

nativeint

A pointer to an unmanaged block of memory, which must be allocated before this method is called.

fDeleteOld

Boolean

true to call the DestroyStructure(IntPtr, Type) method on the ptr parameter before this method copies the data. The block must contain valid data. Note that passing false when the memory block already contains data can lead to a memory leak.

Exceptions

ArgumentException

structure is a reference type that is not a formatted class.

-or-

structure is an instance of a generic type (in the .NET Framework 4.5 and earlier versions only).

Examples

The following example creates a managed structure, transfers it to unmanaged memory using the StructureToPtr method, and then transfers it back to managed memory using the PtrToStructure method.

using System;
using System.Runtime.InteropServices;

public struct Point
{
    public int x;
    public int y;
}

class Example
{

    static void Main()
    {

        // Create a point struct.
        Point p;
        p.x = 1;
        p.y = 1;

        Console.WriteLine("The value of first point is " + p.x + " and " + p.y + ".");

        // Initialize unmanged memory to hold the struct.
        IntPtr pnt = Marshal.AllocHGlobal(Marshal.SizeOf(p));

        try
        {

            // Copy the struct to unmanaged memory.
            Marshal.StructureToPtr(p, pnt, false);

            // Create another point.
            Point anotherP;

            // Set this Point to the value of the
            // Point in unmanaged memory.
            anotherP = (Point)Marshal.PtrToStructure(pnt, typeof(Point));

            Console.WriteLine("The value of new point is " + anotherP.x + " and " + anotherP.y + ".");
        }
        finally
        {
            // Free the unmanaged memory.
            Marshal.FreeHGlobal(pnt);
        }
    }
}

Imports System.Runtime.InteropServices



Public Structure Point
    Public x As Integer
    Public y As Integer
End Structure


Module Example


    Sub Main()

        ' Create a point struct.
        Dim p As Point
        p.x = 1
        p.y = 1

        Console.WriteLine("The value of first point is " + p.x.ToString + " and " + p.y.ToString + ".")

        ' Initialize unmanged memory to hold the struct.
        Dim pnt As IntPtr = Marshal.AllocHGlobal(Marshal.SizeOf(p))

        Try

            ' Copy the struct to unmanaged memory.
            Marshal.StructureToPtr(p, pnt, False)

            ' Create another point.
            Dim anotherP As Point

            ' Set this Point to the value of the 
            ' Point in unmanaged memory. 
            anotherP = CType(Marshal.PtrToStructure(pnt, GetType(Point)), Point)

            Console.WriteLine("The value of new point is " + anotherP.x.ToString + " and " + anotherP.y.ToString + ".")

        Finally
            ' Free the unmanaged memory.
            Marshal.FreeHGlobal(pnt)
        End Try

    End Sub
End Module

Remarks

If structure is a value type, it can be boxed or unboxed. If it is boxed, it is unboxed before copying.

A formatted class is a reference type whose layout is specified by the StructLayoutAttribute attribute, as either LayoutKind.Explicit or LayoutKind.Sequential.

StructureToPtr copies the contents of structure to the pre-allocated block of memory that the ptr parameter points to. If structure contains reference types that marshal to COM interface pointers (interfaces, classes without layout, and System.Object), the managed objects are kept alive with reference counts. All other reference types (for example, strings and arrays) are marshaled to copies. To release these managed or unmanaged objects, you must call the Marshal.DestroyStructure method before you free the memory block.

If you use the StructureToPtr method to copy a different instance to the memory block at a later time, specify true for fDeleteOld to remove reference counts for reference types in the previous instance. Otherwise, the managed reference types and unmanaged copies are effectively leaked.

The overall pattern for using StructureToPtr is as follows:

1. On the first call to the StructureToPtr method after a memory block has been allocated, fDeleteOld must be false, because there are no contents to clear.

   Important

   Specify true for fDeleteOld only if the block contains valid data.

2. If you copy a different instance to the memory block, and the object contains reference types, fDeleteOld must be true to free reference types in the old contents.

3. If the object contains reference types, you must call the DestroyStructure method before you free the memory block.

Note

To pin an existing structure instead of copying it, use the System.Runtime.InteropServices.GCHandle type to create a pinned handle for the structure. For details on how to pin, see Copying and Pinning.

See also

• DestroyStructure(IntPtr, Type)
• GCHandle

StructureToPtr<T>(T, IntPtr, Boolean)

Source:

Marshal.cs

Marshals data from a managed object of a specified type to an unmanaged block of memory.

public:
generic <typename T>
 static void StructureToPtr(T structure, IntPtr ptr, bool fDeleteOld);

public static void StructureToPtr<T> (T structure, IntPtr ptr, bool fDeleteOld);

static member StructureToPtr : 'T * nativeint * bool -> unit

Public Shared Sub StructureToPtr(Of T) (structure As T, ptr As IntPtr, fDeleteOld As Boolean)

Type Parameters

T

The type of the managed object.

Parameters

structure

T

A managed object that holds the data to be marshaled. The object must be a structure or an instance of a formatted class.

ptr

IntPtr

nativeint

A pointer to an unmanaged block of memory, which must be allocated before this method is called.

fDeleteOld

Boolean

true to call the DestroyStructure<T>(IntPtr) method on the ptr parameter before this method copies the data. The block must contain valid data. Note that passing false when the memory block already contains data can lead to a memory leak.

Exceptions

ArgumentException

structure is a reference type that is not a formatted class.

Remarks

A formatted class is a reference type whose layout is specified by the StructLayoutAttribute attribute, as either LayoutKind.Explicit or LayoutKind.Sequential.

StructureToPtr<T>(T, IntPtr, Boolean) copies the contents of structure to the pre-allocated block of memory that the ptr parameter points to. If structure contains reference types that marshal to COM interface pointers (interfaces, classes without layout, and System.Object), the managed objects are kept alive with reference counts. All other reference types (for example, strings and arrays) are marshaled to copies. To release these managed or unmanaged objects, you must call the DestroyStructure<T>(IntPtr) method before you free the memory block.

If you use the StructureToPtr<T>(T, IntPtr, Boolean) method to copy a different instance to the memory block at a later time, specify true for fDeleteOld to remove reference counts for reference types in the previous instance. Otherwise, the managed reference types and unmanaged copies are effectively leaked.

The overall pattern for using StructureToPtr<T>(T, IntPtr, Boolean) is as follows:

1. On the first call to the StructureToPtr method after a memory block has been allocated, fDeleteOld must be false, because there are no contents to clear.

   Important

   Specify true for fDeleteOld only if the block contains valid data.

2. If you copy a different instance to the memory block, and the object contains reference types, fDeleteOld must be true to free reference types in the old contents.

3. If the object contains reference types, you must call the DestroyStructure method before you free the memory block.

Note

To pin an existing structure instead of copying it, use the System.Runtime.InteropServices.GCHandle type to create a pinned handle for the structure. For details on how to pin, see Copying and Pinning.

See also

• DestroyStructure<T>(IntPtr)
• GCHandle