Marshaling Different Types of Arrays
This sample demonstrates how to pass the following types of arrays:
Array of integers by value.
Array of integers by reference, which can be resized.
Multidimensional array (matrix) of integers by value.
Array of strings by value.
Array of structures with integers.
Array of structures with strings.
Unless an array is explicitly marshaled by reference, the default behavior marshals the array as an In parameter. You can change this behavior by applying the InAttribute and OutAttribute attributes explicitly.
The Arrays sample uses the following unmanaged functions, shown with their original function declaration:
TestArrayOfInts exported from PinvokeLib.dll.
int TestArrayOfInts(int* pArray, int pSize);TestRefArrayOfInts exported from PinvokeLib.dll.
int TestRefArrayOfInts(int** ppArray, int* pSize);TestMatrixOfInts exported from PinvokeLib.dll.
int TestMatrixOfInts(int pMatrix[][COL_DIM], int row);TestArrayOfStrings exported from PinvokeLib.dll.
int TestArrayOfStrings(char** ppStrArray, int size);TestArrayOfStructs exported from PinvokeLib.dll.
int TestArrayOfStructs(MYPOINT* pPointArray, int size);TestArrayOfStructs2 exported from PinvokeLib.dll.
int TestArrayOfStructs2 (MYPERSON* pPersonArray, int size);
PinvokeLib.dll is a custom unmanaged library that contains implementations for the previously listed functions and two structure variables, MYPOINT and MYPERSON. The structures contain the following elements:
typedef struct _MYPOINT
{
int x;
int y;
} MYPOINT;
typedef struct _MYPERSON
{
char* first;
char* last;
} MYPERSON;
In this sample, the MyPoint and MyPerson structures contain embedded types. The StructLayoutAttribute attribute is set to ensure that the members are arranged in memory sequentially, in the order in which they appear.
The LibWrap class contains a set of methods called by the App class. For specific details about passing arrays, see the comments in the following sample. An array, which is a reference type, is passed as an In parameter by default. For the caller to receive the results, InAttribute and OutAttribute must be applied explicitly to the argument containing the array.
The source code for the following code examples is provided by the .NET Framework Platform Invoke Technology Sample.
Declaring Prototypes
' Declares a managed structure for each unmanaged structure.
< StructLayout( LayoutKind.Sequential )> _
Public Structure MyPoint
Public x As Integer
Public y As Integer
Public Sub New( x As Integer, y As Integer )
Me.x = x
Me.y = y
End Sub 'New
End Structure 'MyPoint
< StructLayout( LayoutKind.Sequential, CharSet:=CharSet.Ansi )> _
Public Structure MyPerson
Public first As String
Public last As String
Public Sub New( first As String, last As String )
Me.first = first
Me.last = last
End Sub 'New
End Structure 'MyPerson
Public Class LibWrap
' Declares a managed prototype for an array of integers by value.
' The array size cannot be changed, but the array is copied back.
Declare Function TestArrayOfInts Lib "..\LIB\PinvokeLib.dll" ( _
<[In], Out> ByVal myArray() As Integer, ByVal size As Integer ) _
As Integer
' Declares managed prototype for an array of integers by reference.
' The array size can change, but the array is not copied back
' automatically because the marshaler does not know the resulting size.
' The copy must be performed manually.
Declare Function TestRefArrayOfInts Lib "..\LIB\PinvokeLib.dll" ( _
ByRef myArray As IntPtr, ByRef size As Integer ) As Integer
' Declares a managed prototype for a matrix of integers by value.
Declare Function TestMatrixOfInts Lib "..\LIB\PinvokeLib.dll" ( _
<[In], Out> ByVal matrix(,) As Integer, ByVal row As Integer ) _
As Integer
' Declares a managed prototype for an array of strings by value.
Declare Function TestArrayOfStrings Lib "..\LIB\PinvokeLib.dll" ( _
<[In], Out> ByVal strArray() As String, ByVal size As Integer ) _
As Integer
' Declares a managed prototype for an array of structures with
' integers.
Declare Function TestArrayOfStructs Lib "..\LIB\PinvokeLib.dll" ( _
<[In], Out> ByVal pointArray() As MyPoint, _
ByVal size As Integer ) As Integer
' Declares a managed prototype for an array of structures with strings.
Declare Function TestArrayOfStructs2 Lib "..\LIB\PinvokeLib.dll" ( _
<[In], Out> ByVal personArray() As MyPerson, ByVal size _
As Integer ) As Integer
End Class 'LibWrap
// Declares a managed structure for each unmanaged structure.
[ StructLayout( LayoutKind.Sequential )]
public struct MyPoint
{
public int x;
public int y;
public MyPoint( int x, int y )
{
this.x = x;
this.y = y;
}
}
[ StructLayout( LayoutKind.Sequential, CharSet=CharSet.Ansi )]
public struct MyPerson
{
public String first;
public String last;
public MyPerson( String first, String last )
{
this.first = first;
this.last = last;
}
}
public class LibWrap
{
// Declares a managed prototype for an array of integers by value.
// The array size cannot be changed, but the array is copied back.
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern int TestArrayOfInts([In, Out] int[] array, int size );
// Declares a managed prototype for an array of integers by reference.
// The array size can change, but the array is not copied back
// automatically because the marshaler does not know the resulting size.
// The copy must be performed manually.
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern int TestRefArrayOfInts( ref IntPtr array,
ref int size );
// Declares a managed prototype for a matrix of integers by value.
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern int TestMatrixOfInts([In, Out] int[,] pMatrix,
int row );
// Declares a managed prototype for an array of strings by value.
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern int TestArrayOfStrings( [In, Out]
String[] stringArray, int size );
// Declares a managed prototype for an array of structures with integers.
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern int TestArrayOfStructs([In, Out] MyPoint[]
pointArray, int size );
// Declares a managed prototype for an array of structures with strings.
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern int TestArrayOfStructs2( [In, Out]
MyPerson[] personArray, int size );
}
Calling Functions
Public Class App
Public Shared Sub Main()
' array ByVal
Dim array1(9) As Integer
Console.WriteLine( "Integer array passed ByVal before call:" )
Dim i As Integer
For i = 0 To array1.Length - 1
array1(i) = i
Console.Write( " " & array1(i) )
Next i
Dim sum1 As Integer = LibWrap.TestArrayOfInts( array1, array1._
Length )
Console.WriteLine( ControlChars.CrLf & "Sum of elements:" & sum1 )
Console.WriteLine( ControlChars.CrLf & "Integer array passed _
ByVal after call:" )
For Each i In array1
Console.Write( " " & i )
Next i
' array ByRef
Dim array2(9) As Integer
Dim arraySize As Integer = array2.Length
Console.WriteLine( ControlChars.CrLf & ControlChars.CrLf & _
"Integer array passed ByRef before call:" )
For i = 0 To array2.Length - 1
array2(i) = i
Console.Write( " " & array2(i) )
Next i
Dim buffer As IntPtr = Marshal.AllocCoTaskMem( Marshal.SizeOf( _
arraySize ) * array2.Length )
Marshal.Copy( array2, 0, buffer, array2.Length )
Dim sum2 As Integer = LibWrap.TestRefArrayOfInts( buffer, _
arraySize )
Console.WriteLine( ControlChars.CrLf & "Sum of elements:" & sum2 )
If arraySize > 0 Then
Dim arrayRes( arraySize - 1 ) As Integer
Marshal.Copy( buffer, arrayRes, 0, arraySize )
Marshal.FreeCoTaskMem( buffer )
Console.WriteLine( ControlChars.CrLf & "Integer array _
passed ByRef after call:" )
For Each i In arrayRes
Console.Write( " " & i )
Next i
Else
Console.WriteLine( ControlChars.CrLf & "Array after call _
is empty" )
End If
' matrix ByVal
Const [DIM] As Integer = 4
Dim matrix([DIM], [DIM]) As Integer
Console.WriteLine( ControlChars.CrLf & ControlChars.CrLf & _
"Matrix before call:" )
For i = 0 To [DIM]
Dim j As Integer
For j = 0 To [DIM]
matrix(i, j) = j
Console.Write( " " & matrix(i, j) )
Next j
Console.WriteLine( "" )
Next i
Dim sum3 As Integer = LibWrap.TestMatrixOfInts( matrix, [DIM] + 1 )
Console.WriteLine( ControlChars.CrLf & "Sum of elements:" & sum3 )
Console.WriteLine( ControlChars.CrLf & "Matrix after call:" )
For i = 0 To [DIM]
Dim j As Integer
For j = 0 To [DIM]
Console.Write( " " & matrix(i, j) )
Next j
Console.WriteLine( "" )
Next i
' string array ByVal
Dim strArray As String() = { "one", "two", "three", "four", _
"five" }
Console.WriteLine( ControlChars.CrLf & ControlChars.CrLf & _
"String array before call:" )
Dim s As String
For Each s In strArray
Console.Write( " " & s )
Next s
Dim lenSum As Integer = LibWrap.TestArrayOfStrings( _
strArray, strArray.Length )
Console.WriteLine( ControlChars.CrLf & _
"Sum of string lengths:" & lenSum )
Console.WriteLine( ControlChars.CrLf & "String array after call:" )
For Each s In strArray
Console.Write( " " & s )
Next s
' struct array ByVal
Dim points As MyPoint() = { New MyPoint(1, 1), New MyPoint(2, 2), _
New MyPoint(3, 3) }
Console.WriteLine( ControlChars.CrLf & ControlChars.CrLf & _
"Points array before call:" )
Dim p As MyPoint
For Each p In points
Console.WriteLine( "x = {0}, y = {1}", p.x, p.y )
Next p
Dim allSum As Integer = LibWrap.TestArrayOfStructs( points, _
points.Length )
Console.WriteLine( ControlChars.CrLf & "Sum of points:" & allSum )
Console.WriteLine( ControlChars.CrLf & "Points array after call:" )
For Each p In points
Console.WriteLine( "x = {0}, y = {1}", p.x, p.y )
Next p
' struct with strings array ByVal
Dim persons As MyPerson() = { _New MyPerson( "Kim", "Akers" ), _
New MyPerson( "Adam", "Barr" ), _
New MyPerson( "Jo", "Brown" )}
Console.WriteLine( ControlChars.CrLf & ControlChars.CrLf & _
"Persons array before call:" )
Dim pe As MyPerson
For Each pe In persons
Console.WriteLine( "first = {0}, last = {1}", pe.first, pe.last )
Next pe
Dim namesSum As Integer = LibWrap.TestArrayOfStructs2( persons, _
persons.Length )
Console.WriteLine( ControlChars.CrLf & "Sum of name lengths:" & _
namesSum )
Console.WriteLine( ControlChars.CrLf & ControlChars._
CrLf & "Persons array after call:" )
For Each pe In persons
Console.WriteLine( "first = {0}, last = {1}", pe.first, pe.last )
Next pe
End Sub 'Main
End Class 'App
public class App
{
public static void Main()
{
// array ByVal
int[] array1 = new int[ 10 ];
Console.WriteLine( "Integer array passed ByVal before call:" );
for( int i = 0; i < array1.Length; i++ )
{
array1[ i ] = i;
Console.Write( " " + array1[ i ] );
}
int sum1 = LibWrap.TestArrayOfInts( array1, array1.Length );
Console.WriteLine( "\nSum of elements:" + sum1 );
Console.WriteLine( "\nInteger array passed ByVal after call:" );
foreach( int i in array1 )
{
Console.Write( " " + i );
}
// array ByRef
int[] array2 = new int[ 10 ];
int size = array2.Length;
Console.WriteLine( "\n\nInteger array passed ByRef before call:" );
for( int i = 0; i < array2.Length; i++ )
{
array2[ i ] = i;
Console.Write( " " + array2[ i ] );
}
IntPtr buffer = Marshal.AllocCoTaskMem( Marshal.SizeOf( size )
* array2.Length );
Marshal.Copy( array2, 0, buffer, array2.Length );
int sum2 = LibWrap.TestRefArrayOfInts( ref buffer, ref size );
Console.WriteLine( "\nSum of elements:" + sum2 );
if( size > 0 )
{
int[] arrayRes = new int[ size ];
Marshal.Copy( buffer, arrayRes, 0, size );
Marshal.FreeCoTaskMem( buffer );
Console.WriteLine( "\nInteger array passed ByRef after call:" );
foreach( int i in arrayRes )
{
Console.Write( " " + i );
}
}
else
Console.WriteLine( "\nArray after call is empty" );
// matrix ByVal
const int DIM = 5;
int[,] matrix = new int[ DIM, DIM ];
Console.WriteLine( "\n\nMatrix before call:" );
for( int i = 0; i < DIM; i++ )
{
for( int j = 0; j < DIM; j++ )
{
matrix[ i, j ] = j;
Console.Write( " " + matrix[ i, j ] );
}
Console.WriteLine( "" );
}
int sum3 = LibWrap.TestMatrixOfInts( matrix, DIM );
Console.WriteLine( "\nSum of elements:" + sum3 );
Console.WriteLine( "\nMatrix after call:" );
for( int i = 0; i < DIM; i++ )
{
for( int j = 0; j < DIM; j++ )
{
Console.Write( " " + matrix[ i, j ] );
}
Console.WriteLine( "" );
}
// string array ByVal
String[] strArray = { "one", "two", "three", "four", "five" };
Console.WriteLine( "\n\nString array before call:" );
foreach( String s in strArray )
Console.Write( " "+ s );
int lenSum = LibWrap.TestArrayOfStrings( strArray, strArray.Length );
Console.WriteLine( "\nSum of string lengths:" + lenSum );
Console.WriteLine( "\nString array after call:" );
foreach( String s in strArray )
{
Console.Write( " " + s );
}
// struct array ByVal
MyPoint[] points = { new MyPoint(1,1), new MyPoint(2,2), new MyPoint(3,3) };
Console.WriteLine( "\n\nPoints array before call:" );
foreach( MyPoint p in points )
Console.WriteLine( "x = {0}, y = {1}", p.x, p.y );
int allSum = LibWrap.TestArrayOfStructs( points, points.Length );
Console.WriteLine( "\nSum of points:" + allSum );
Console.WriteLine( "\nPoints array after call:" );
foreach( MyPoint p in points )
Console.WriteLine( "x = {0}, y = {1}", p.x, p.y );
// struct with strings array ByVal
MyPerson[] persons = { new MyPerson( "Kim", "Akers" ),
new MyPerson( "Adam", "Barr" ), new MyPerson( "Jo", "Brown" )};
Console.WriteLine( "\n\nPersons array before call:" );
foreach( MyPerson pe in persons )
Console.WriteLine( "first = {0}, last = {1}", pe.first, pe.last );
int namesSum = LibWrap.TestArrayOfStructs2( persons, persons.Length );
Console.WriteLine( "\nSum of name lengths:" + namesSum );
Console.WriteLine( "\n\nPersons array after call:" );
foreach( MyPerson pe in persons )
Console.WriteLine( "first = {0}, last = {1}", pe.first, pe.last );
}
}