OutArrayOfStructs 示例
更新：2007 年 11 月
此示例演示如何将包含整数和字符串的结构数组作为 Out 参数传递给非托管函数。源代码示例包含在 平台调用技术示例 中。
此示例演示使用 Marshal 类和使用不安全代码如何调用本机函数。
此示例使用包装函数和 PinvokeLib.dll 中定义的平台调用（也在源文件中提供）。它使用 TestOutArrayOfStructs 函数和 MYSTRSTRUCT2 结构。该结构包含以下元素：
typedef struct _MYSTRSTRUCT2
{
char* buffer;
UINT size;
} MYSTRSTRUCT2;
MyStruct 类包含 ANSI 字符的字符串对象。CharSet 字段指定 ANSI 格式。MyUnsafeStruct，是一个包含 IntPtr 类型（而不是字符串）的结构。
LibWrap 类包含重载的 TestOutArrayOfStructs 原型方法。如果一个方法将指针声明为参数，则该类应使用 unsafe 关键字加以标记。由于 Visual Basic 2005 无法使用不安全代码，因此重载方法、不安全修饰符和 MyUnsafeStruct 结构都是不必要的。
App 类实现 UsingMarshal 方法，它执行传递数组所需的所有任务。该数组用 out（在 Visual Basic 中为 ByRef）关键字加以标记，以指示数据从被调用方传递给调用方。此实现使用以下 Marshal 类方法：
PtrToStructure，它用于从非托管缓冲区向托管对象封送数据。
DestroyStructure，它用于释放为结构中的字符串保留的内存。
FreeCoTaskMem，它用于释放为该数组保留的内存。
如前所述，C# 允许使用不安全代码，而 Visual Basic 2005 则不允许。在 C# 示例中，UsingUnsafe 是一个替换方法实现，它使用指针而不是 Marshal 类来传回包含 MyUnsafeStruct 结构的数组。
声明原型
' Declares a class member for each structure element.
< StructLayout( LayoutKind.Sequential, CharSet:=CharSet.Ansi )> _
Public Class MyStruct
Public buffer As String
Public someSize As Integer
End Class 'MyStruct
Public Class LibWrap
' Declares a managed prototype for the unmanaged function.
Declare Sub TestOutArrayOfStructs Lib "..\\LIB\\PinvokeLib.dll" ( _
ByRef arrSize As Integer, ByRef outArray As IntPtr )
End Class 'LibWrap
// Declares a class member for each structure element.
[ StructLayout( LayoutKind.Sequential, CharSet=CharSet.Ansi )]
public class MyStruct
{
public String buffer;
public int size;
}
// Declares a structure with a pointer.
[ StructLayout( LayoutKind.Sequential )]
public struct MyUnsafeStruct
{
public IntPtr buffer;
public int size;
}
public unsafe class LibWrap
{
// Declares managed prototypes for the unmanaged function.
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern void TestOutArrayOfStructs( out int size,
out IntPtr outArray );
[ DllImport( "..\\LIB\\PinvokeLib.dll" )]
public static extern void TestOutArrayOfStructs( out int size,
MyUnsafeStruct** outArray );
}
调用函数
Public Class App
Public Shared Sub Main()
Console.WriteLine( ControlChars.CrLf & "Using marshal class" & _
ControlChars.CrLf )
UsingMarshal()
'Visual Basic 2005 cannot use unsafe code.
End Sub 'Main
Public Shared Sub UsingMarshal()
Dim arrSize As Integer
Dim outArray As IntPtr
LibWrap.TestOutArrayOfStructs( arrSize, outArray )
Dim manArray(arrSize - 1) As MyStruct
Dim current As IntPtr = outArray
Dim i As Integer
For i = 0 To arrSize - 1
manArray(i) = New MyStruct()
Marshal.PtrToStructure( current, manArray(i))
Marshal.DestroyStructure( current, GetType( MyStruct ))
current = IntPtr.op_explicit( current.ToInt64() _
+ Marshal.SizeOf( manArray(i) ))
Console.WriteLine( "Element {0}: {1} {2}", i, manArray(i)._
buffer, manArray(i).someSize )
Next i
Marshal.FreeCoTaskMem( outArray )
End Sub 'UsingMarshal
End Class 'App
public class App
{
public static void Main()
{
Console.WriteLine( "\nUsing marshal class\n" );
UsingMarshal();
Console.WriteLine( "\nUsing unsafe code\n" );
UsingUnsafe();
}
public static void UsingMarshal()
{
int size;
IntPtr outArray;
LibWrap.TestOutArrayOfStructs( out size, out outArray );
MyStruct[] manArray = new MyStruct[ size ];
IntPtr current = outArray;
for( int i = 0; i < size; i++ )
{
manArray[ i ] = new MyStruct();
Marshal.PtrToStructure( current, manArray[ i ]);
//Marshal.FreeCoTaskMem( (IntPtr)Marshal.ReadInt32( current ));
Marshal.DestroyStructure( current, typeof(MyStruct) );
current = (IntPtr)((long)current +
Marshal.SizeOf( manArray[ i ] ));
Console.WriteLine( "Element {0}: {1} {2}", i,
manArray[ i ].buffer, manArray[ i ].size );
}
Marshal.FreeCoTaskMem( outArray );
}
public static unsafe void UsingUnsafe()
{
int size;
MyUnsafeStruct* pResult;
LibWrap.TestOutArrayOfStructs( out size, &pResult );
MyUnsafeStruct* pCurrent = pResult;
for( int i = 0; i < size; i++, pCurrent++ )
{
Console.WriteLine( "Element {0}: {1} {2}", i,
Marshal.PtrToStringAnsi( pCurrent->buffer ), pCurrent->size );
Marshal.FreeCoTaskMem( pCurrent->buffer );
}
Marshal.FreeCoTaskMem( (IntPtr)pResult );
}
}