封送處理類別、結構和等位

發行項
03/11/2024

在 .NET Framework 中，類別和結構相類似。兩者都可以有欄位、屬性和事件。也可以有靜態和非靜態方法。一個值得注意的差異在於結構是實值類型，而類別是參考類型。

下表列出類別、結構及等位的封送處理選項，並描述其用法，以及提供對應平台的叫用範例連結。

類型	描述	範例
傳值呼叫	做為 In/Out 參數，如 Managed 案例，會傳遞具有整數成員的類別。	SysTime 範例
結構傳值。	傳遞結構做為 In 參數。	結構範例
結構傳址。	傳遞結構做為 In/Out 參數。	OSInfo 範例
具有巢狀結構 (扁平化) 的結構。	傳遞類別，表示具有 Unmanaged 函式中巢狀結構的結構。在 Managed 原型中，結構被扁平化為一個大的結構。	FindFile 範例
指標指向另一個結構的結構。	傳遞一個結構，其包含的指標指向第二個做為成員的結構。	結構範例
整數傳值的結構陣列。	將僅包含整數的結構陣列做為 In/Out 參數傳遞。可變更陣列的成員。	陣列範例
整數結構和傳址字串的陣列。	傳遞包含整數和字串做為 Out 參數的結構陣列。所呼叫的函式會配置此陣列的記憶體。	OutArrayOfStructs 範例
具有實值類型的等位。	傳遞具有實值類型的等位 (整數和雙精度浮點數)。	等位範例
具有混合類型的等位。	傳遞具有混合類型的等位 (整數和字串)。	等位範例
具有平台特定配置的結構。	傳遞具有原生封裝定義的類型。	平台範例
在結構中的 null 值。	傳遞 Null 參考 (在 Visual Basic 中為 Nothing)，而非實值型別的參考。	HandleRef 範例

結構範例

這個範例示範如何傳遞指向第二個結構的結構、傳遞具有內嵌結構的結構，以及傳遞具有內嵌陣列的結構。

本結構範例會使用下列 Unmanaged 函式，和其原始函式宣告，如下所示：

從 PinvokeLib.dll 匯出的 TestStructInStruct。
```
int TestStructInStruct(MYPERSON2* pPerson2);
```
從 PinvokeLib.dll 匯出的 TestStructInStruct3。
```
void TestStructInStruct3(MYPERSON3 person3);
```

從 PinvokeLib.dll 匯出的 TestArrayInStruct。

void TestArrayInStruct(MYARRAYSTRUCT* pStruct);

PinvokeLib.dll 是自訂的 Unmanaged 程式庫，其中包含先前所列出函式和四個結構的實作：MYPERSON、MYPERSON2、MYPERSON3 和 MYARRAYSTRUCT。這些結構包含下列項目：

typedef struct _MYPERSON
{
   char* first;
   char* last;
} MYPERSON, *LP_MYPERSON;

typedef struct _MYPERSON2
{
   MYPERSON* person;
   int age;
} MYPERSON2, *LP_MYPERSON2;

typedef struct _MYPERSON3
{
   MYPERSON person;
   int age;
} MYPERSON3;

typedef struct _MYARRAYSTRUCT
{
   bool flag;
   int vals[ 3 ];
} MYARRAYSTRUCT;

Managed MyPerson、MyPerson2、MyPerson3 和 MyArrayStruct 結構的特性如下：

MyPerson 僅包含字串成員。當傳遞給 Unmanaged 函式時，CharSet 欄位會將字串設定為 ANSI 格式。
MyPerson2 包含 MyPerson 結構的 IntPtr。 IntPtr 類型會取代原始指標的 Unmanaged 結構，因為 .NET Framework 應用程式不會使用指標，除非將程式碼標示為 Unsafe。
MyPerson3 包含 MyPerson 做為內嵌結構。藉由將內嵌結構的項目放在主結構中，可扁平化內嵌於其它結構的結構，或者將它留下做為內嵌結構，如本範例所完成的動作。
MyArrayStruct 包含一個整數的陣列。 MarshalAsAttribute 屬性會將 UnmanagedType 列舉值設定為 ByValArray，用來表示陣列項目數。

對於本範例的所有結構，套用 StructLayoutAttribute 屬性來確定此成員以其顯示的順序循序排列在記憶體中。

NativeMethods 類別包含 TestStructInStruct、TestStructInStruct3 及 TestArrayInStruct 方法的 Managed 原型，這些方法由 App 類別所呼叫。每一個原型會宣告單一參數，如下所示：

TestStructInStruct 宣告一個參考給 MyPerson2 類型做為它的參數。
TestStructInStruct3 宣告 MyPerson3 類型做為它的參數，並以傳值方式傳遞參數。
TestArrayInStruct 宣告一個參考給 MyArrayStruct 類型做為它的參數。

除非此參數包含 ref 關鍵字 (在 Visual Basic 中為 ByRef)，否則作為方法引數的結構會以傳值方式傳遞。例如， TestStructInStruct 方法會傳遞對於類型物件 MyPerson2 的參考 (位址的值) 給 Unmanaged 程式碼。若要管理 MyPerson2 指向的結構，此範例會建立指定大小的緩衝區，並藉由合併 Marshal.AllocCoTaskMem 和 Marshal.SizeOf 方法，傳回其位址。接下來，範例會將 Managed 結構的內容複製到 Unmanaged 緩衝區。最後，此範例會使用 Marshal.PtrToStructure 方法自 Unmanaged 緩衝區封送處理資料到 Managed 物件，並以 Marshal.FreeCoTaskMem 方法來釋放 Unmanaged 記憶體區塊。

宣告原型

// Declares a managed structure for each unmanaged structure.
[StructLayout(LayoutKind::Sequential, CharSet = CharSet::Ansi)]
public value struct MyPerson
{
public:
    String^ first;
    String^ last;
};

[StructLayout(LayoutKind::Sequential)]
public value struct MyPerson2
{
public:
    IntPtr person;
    int age;
};

[StructLayout(LayoutKind::Sequential)]
public value struct MyPerson3
{
public:
    MyPerson person;
    int age;
};

[StructLayout(LayoutKind::Sequential)]
public value struct MyArrayStruct
{
public:
    bool flag;
    [MarshalAs(UnmanagedType::ByValArray, SizeConst = 3)]
    array<int>^ vals;
};

private ref class NativeMethods
{
public:
    // Declares a managed prototype for unmanaged function.
    [DllImport("..\\LIB\\PinvokeLib.dll")]
    static int TestStructInStruct(MyPerson2% person2);

    [DllImport("..\\LIB\\PinvokeLib.dll")]
    static int TestStructInStruct3(MyPerson3 person3);

    [DllImport("..\\LIB\\PinvokeLib.dll")]
    static int TestArrayInStruct(MyArrayStruct% myStruct);
};

// Declares a managed structure for each unmanaged structure.
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct MyPerson
{
    public string first;
    public string last;
}

[StructLayout(LayoutKind.Sequential)]
public struct MyPerson2
{
    public IntPtr person;
    public int age;
}

[StructLayout(LayoutKind.Sequential)]
public struct MyPerson3
{
    public MyPerson person;
    public int age;
}

[StructLayout(LayoutKind.Sequential)]
public struct MyArrayStruct
{
    public bool flag;

    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 3)]
    public int[] vals;
}

internal static class NativeMethods
{
    // Declares a managed prototype for unmanaged function.
    [DllImport("..\\LIB\\PinvokeLib.dll", CallingConvention = CallingConvention.Cdecl)]
    internal static extern int TestStructInStruct(ref MyPerson2 person2);

    [DllImport("..\\LIB\\PinvokeLib.dll", CallingConvention = CallingConvention.Cdecl)]
    internal static extern int TestStructInStruct3(MyPerson3 person3);

    [DllImport("..\\LIB\\PinvokeLib.dll", CallingConvention = CallingConvention.Cdecl)]
    internal static extern int TestArrayInStruct(ref MyArrayStruct myStruct);
}

' Declares a managed structure for each unmanaged structure.
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Ansi)>
Public Structure MyPerson
    Public first As String
    Public last As String
End Structure

<StructLayout(LayoutKind.Sequential)>
Public Structure MyPerson2
    Public person As IntPtr
    Public age As Integer
End Structure

<StructLayout(LayoutKind.Sequential)>
Public Structure MyPerson3
    Public person As MyPerson
    Public age As Integer
End Structure

<StructLayout(LayoutKind.Sequential)>
Public Structure MyArrayStruct
    Public flag As Boolean
    <MarshalAs(UnmanagedType.ByValArray, SizeConst:=3)>
    Public vals As Integer()
End Structure

Friend Class NativeMethods
    ' Declares managed prototypes for unmanaged functions.
    <DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
    Friend Shared Function TestStructInStruct(
        ByRef person2 As MyPerson2) As Integer
    End Function

    <DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
    Friend Shared Function TestStructInStruct3(
        ByVal person3 As MyPerson3) As Integer
    End Function

    <DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
    Friend Shared Function TestArrayInStruct(
        ByRef myStruct As MyArrayStruct) As Integer
    End Function
End Class

呼叫函式

public ref class App
{
public:
    static void Main()
    {
        // Structure with a pointer to another structure.
        MyPerson personName;
        personName.first = "Mark";
        personName.last = "Lee";

        MyPerson2 personAll;
        personAll.age = 30;

        IntPtr buffer = Marshal::AllocCoTaskMem(Marshal::SizeOf(personName));
        Marshal::StructureToPtr(personName, buffer, false);

        personAll.person = buffer;

        Console::WriteLine("\nPerson before call:");
        Console::WriteLine("first = {0}, last = {1}, age = {2}",
            personName.first, personName.last, personAll.age);

        int res = NativeMethods::TestStructInStruct(personAll);

        MyPerson personRes =
            (MyPerson)Marshal::PtrToStructure(personAll.person,
                MyPerson::typeid);

        Marshal::FreeCoTaskMem(buffer);

        Console::WriteLine("Person after call:");
        Console::WriteLine("first = {0}, last = {1}, age = {2}",
            personRes.first, personRes.last, personAll.age);

        // Structure with an embedded structure.
        MyPerson3 person3;// = gcnew MyPerson3();
        person3.person.first = "John";
        person3.person.last = "Evans";
        person3.age = 27;
        NativeMethods::TestStructInStruct3(person3);

        // Structure with an embedded array.
        MyArrayStruct myStruct;// = new MyArrayStruct();

        myStruct.flag = false;
        myStruct.vals = gcnew array<int>(3);
        myStruct.vals[0] = 1;
        myStruct.vals[1] = 4;
        myStruct.vals[2] = 9;

        Console::WriteLine("\nStructure with array before call:");
        Console::WriteLine(myStruct.flag);
        Console::WriteLine("{0} {1} {2}", myStruct.vals[0],
            myStruct.vals[1], myStruct.vals[2]);

        NativeMethods::TestArrayInStruct(myStruct);
        Console::WriteLine("\nStructure with array after call:");
        Console::WriteLine(myStruct.flag);
        Console::WriteLine("{0} {1} {2}", myStruct.vals[0],
            myStruct.vals[1], myStruct.vals[2]);
    }
};

public class App
{
    public static void Main()
    {
        // Structure with a pointer to another structure.
        MyPerson personName;
        personName.first = "Mark";
        personName.last = "Lee";

        MyPerson2 personAll;
        personAll.age = 30;

        IntPtr buffer = Marshal.AllocCoTaskMem(Marshal.SizeOf(personName));
        Marshal.StructureToPtr(personName, buffer, false);

        personAll.person = buffer;

        Console.WriteLine("\nPerson before call:");
        Console.WriteLine("first = {0}, last = {1}, age = {2}",
            personName.first, personName.last, personAll.age);

        int res = NativeMethods.TestStructInStruct(ref personAll);

        MyPerson personRes =
            (MyPerson)Marshal.PtrToStructure(personAll.person,
            typeof(MyPerson));

        Marshal.FreeCoTaskMem(buffer);

        Console.WriteLine("Person after call:");
        Console.WriteLine("first = {0}, last = {1}, age = {2}",
            personRes.first, personRes.last, personAll.age);

        // Structure with an embedded structure.
        MyPerson3 person3 = new MyPerson3();
        person3.person.first = "John";
        person3.person.last = "Evans";
        person3.age = 27;
        NativeMethods.TestStructInStruct3(person3);

        // Structure with an embedded array.
        MyArrayStruct myStruct = new MyArrayStruct();

        myStruct.flag = false;
        myStruct.vals = new int[3];
        myStruct.vals[0] = 1;
        myStruct.vals[1] = 4;
        myStruct.vals[2] = 9;

        Console.WriteLine("\nStructure with array before call:");
        Console.WriteLine(myStruct.flag);
        Console.WriteLine("{0} {1} {2}", myStruct.vals[0],
            myStruct.vals[1], myStruct.vals[2]);

        NativeMethods.TestArrayInStruct(ref myStruct);
        Console.WriteLine("\nStructure with array after call:");
        Console.WriteLine(myStruct.flag);
        Console.WriteLine("{0} {1} {2}", myStruct.vals[0],
            myStruct.vals[1], myStruct.vals[2]);
    }
}

Public Class App
    Public Shared Sub Main()
        ' Structure with a pointer to another structure.
        Dim personName As MyPerson
        personName.first = "Mark"
        personName.last = "Lee"

        Dim personAll As MyPerson2
        personAll.age = 30

        Dim buffer As IntPtr = Marshal.AllocCoTaskMem(Marshal.SizeOf(
            personName))
        Marshal.StructureToPtr(personName, buffer, False)

        personAll.person = buffer

        Console.WriteLine(ControlChars.CrLf & "Person before call:")
        Console.WriteLine("first = {0}, last = {1}, age = {2}",
            personName.first, personName.last, personAll.age)

        Dim res As Integer = NativeMethods.TestStructInStruct(personAll)

        Dim personRes As MyPerson =
            CType(Marshal.PtrToStructure(personAll.person,
            GetType(MyPerson)), MyPerson)

        Marshal.FreeCoTaskMem(buffer)

        Console.WriteLine("Person after call:")
        Console.WriteLine("first = {0}, last = {1}, age = {2}",
        personRes.first,
            personRes.last, personAll.age)

        ' Structure with an embedded structure.
        Dim person3 As New MyPerson3()
        person3.person.first = "John"
        person3.person.last = "Evans"
        person3.age = 27
        NativeMethods.TestStructInStruct3(person3)

        ' Structure with an embedded array.
        Dim myStruct As New MyArrayStruct()

        myStruct.flag = False
        Dim array(2) As Integer
        myStruct.vals = array
        myStruct.vals(0) = 1
        myStruct.vals(1) = 4
        myStruct.vals(2) = 9

        Console.WriteLine(vbNewLine + "Structure with array before call:")
        Console.WriteLine(myStruct.flag)
        Console.WriteLine("{0} {1} {2}", myStruct.vals(0),
            myStruct.vals(1), myStruct.vals(2))

        NativeMethods.TestArrayInStruct(myStruct)
        Console.WriteLine(vbNewLine + "Structure with array after call:")
        Console.WriteLine(myStruct.flag)
        Console.WriteLine("{0} {1} {2}", myStruct.vals(0),
            myStruct.vals(1), myStruct.vals(2))
    End Sub
End Class

FindFile 範例

這個範例示範如何傳遞包含第二個內嵌結構的結構給 Unmanaged 函式。它也會示範如何使用 MarshalAsAttribute 屬性在結構內宣告固定長度的陣列。在此範例中，會加入內嵌結構項目至其父結構。如需未扁平化內嵌結構的範例，請參閱結構範例。

FindFile 範例會使用下列 Unmanaged 函式，和其原始函式宣告，如下所示：

從 Kernel32.dll 匯出 FindFirstFile。

HANDLE FindFirstFile(LPCTSTR lpFileName, LPWIN32_FIND_DATA lpFindFileData);

傳遞至函式的原始結構包含下列項目：

typedef struct _WIN32_FIND_DATA
{
  DWORD    dwFileAttributes;
  FILETIME ftCreationTime;
  FILETIME ftLastAccessTime;
  FILETIME ftLastWriteTime;
  DWORD    nFileSizeHigh;
  DWORD    nFileSizeLow;
  DWORD    dwReserved0;
  DWORD    dwReserved1;
  TCHAR    cFileName[ MAX_PATH ];
  TCHAR    cAlternateFileName[ 14 ];
} WIN32_FIND_DATA, *PWIN32_FIND_DATA;

在此範例中， FindData 類別包含原始結構的每個項目所對應的資料成員和內嵌結構。為了取代 2 個原始字元緩衝區，類別會替代字串。 MarshalAsAttribute 會將 UnmanagedType 列舉設定為 ByValTStr，這用來識別出現在 Unmanaged 結構中內嵌固定長度的字元陣列。

NativeMethods 類別包含 FindFirstFile 方法的 Managed 原型，會傳遞 FindData 類別做為參數。參數必須以 InAttribute 和 OutAttribute 屬性宣告，因為根據預設，會傳遞參考類型的類別做為 In 參數。

宣告原型

// Declares a class member for each structure element.
[StructLayout(LayoutKind::Sequential, CharSet = CharSet::Auto)]
public ref class FindData
{
public:
    int  fileAttributes;
    // creationTime was an embedded FILETIME structure.
    int  creationTime_lowDateTime;
    int  creationTime_highDateTime;
    // lastAccessTime was an embedded FILETIME structure.
    int  lastAccessTime_lowDateTime;
    int  lastAccessTime_highDateTime;
    // lastWriteTime was an embedded FILETIME structure.
    int  lastWriteTime_lowDateTime;
    int  lastWriteTime_highDateTime;
    int  nFileSizeHigh;
    int  nFileSizeLow;
    int  dwReserved0;
    int  dwReserved1;
    [MarshalAs(UnmanagedType::ByValTStr, SizeConst = 260)]
    String^  fileName;
    [MarshalAs(UnmanagedType::ByValTStr, SizeConst = 14)]
    String^  alternateFileName;
};

private ref class NativeMethods
{
public:
    // Declares a managed prototype for the unmanaged function.
    [DllImport("Kernel32.dll", CharSet = CharSet::Auto)]
    static IntPtr FindFirstFile(String^ fileName, [In, Out]
        FindData^ findFileData);
};

// Declares a class member for each structure element.
[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Auto)]
public class FindData
{
    public int fileAttributes = 0;
    // creationTime was an embedded FILETIME structure.
    public int creationTime_lowDateTime = 0;
    public int creationTime_highDateTime = 0;
    // lastAccessTime was an embedded FILETIME structure.
    public int lastAccessTime_lowDateTime = 0;
    public int lastAccessTime_highDateTime = 0;
    // lastWriteTime was an embedded FILETIME structure.
    public int lastWriteTime_lowDateTime = 0;
    public int lastWriteTime_highDateTime = 0;
    public int nFileSizeHigh = 0;
    public int nFileSizeLow = 0;
    public int dwReserved0 = 0;
    public int dwReserved1 = 0;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 260)]
    public string fileName = null;
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 14)]
    public string alternateFileName = null;
}

internal static class NativeMethods
{
    // Declares a managed prototype for the unmanaged function.
    [DllImport("Kernel32.dll", CharSet = CharSet.Auto)]
    internal static extern IntPtr FindFirstFile(
        string fileName, [In, Out] FindData findFileData);
}

' Declares a class member for each structure element.
<StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Auto)>
Public Class FindData
    Public fileAttributes As Integer = 0
    ' creationTime was a by-value FILETIME structure.
    Public creationTime_lowDateTime As Integer = 0
    Public creationTime_highDateTime As Integer = 0
    ' lastAccessTime was a by-value FILETIME structure.
    Public lastAccessTime_lowDateTime As Integer = 0
    Public lastAccessTime_highDateTime As Integer = 0
    ' lastWriteTime was a by-value FILETIME structure.
    Public lastWriteTime_lowDateTime As Integer = 0
    Public lastWriteTime_highDateTime As Integer = 0
    Public nFileSizeHigh As Integer = 0
    Public nFileSizeLow As Integer = 0
    Public dwReserved0 As Integer = 0
    Public dwReserved1 As Integer = 0
    <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=260)>
    Public fileName As String = Nothing
    <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=14)>
    Public alternateFileName As String = Nothing
End Class

Friend Class NativeMethods
    ' Declares a managed prototype for the unmanaged function.
    Friend Declare Auto Function FindFirstFile Lib "Kernel32.dll" (
        ByVal fileName As String, <[In], Out> ByVal findFileData As _
        FindData) As IntPtr
End Class

呼叫函式

public ref class App
{
public:
    static void Main()
    {
        FindData^ fd = gcnew FindData();
        IntPtr handle = NativeMethods::FindFirstFile("C:\\*.*", fd);
        Console::WriteLine("The first file: {0}", fd->fileName);
    }
};

public class App
{
    public static void Main()
    {
        FindData fd = new FindData();
        IntPtr handle = NativeMethods.FindFirstFile("C:\\*.*", fd);
        Console.WriteLine($"The first file: {fd.fileName}");
    }
}

Public Class App
    Public Shared Sub Main()
        Dim fd As New FindData()
        Dim handle As IntPtr = NativeMethods.FindFirstFile("C:\*.*", fd)
        Console.WriteLine($"The first file: {fd.fileName}")
    End Sub
End Class

等位範例

這個範例示範如何傳遞結構至需要等位的 Unmanged 函式，該結構僅包含實值類型、包含實值類型的結構和一個做為參數的字串。等位表示可由兩個或多個變數共用的記憶體位置。

Unions 範例會使用下列 Unmanaged 函式，和其原始函式宣告，如下所示：

從 PinvokeLib.dll 匯出的 TestUnion。
```
void TestUnion(MYUNION u, int type);
```

PinvokeLib.dll 是自訂的 Unmanaged 程式庫，其中包含先前所列出函式以及 MYUNION 和 MYUNION2 這兩個等位的實作。此等位包含下列項目：

union MYUNION
{
    int number;
    double d;
}

union MYUNION2
{
    int i;
    char str[128];
};

在 Managed 程式碼中，會定義等位為結構。 MyUnion 結構包含兩個做為其成員的實值類型：整數和雙精度浮點數。設定 StructLayoutAttribute 屬性來控制每個資料成員的精確位置。 FieldOffsetAttribute 屬性會提供等位的 Unmanaged 表示中的欄位實體位置。請注意這兩個成員具有相同的位移值，所以成員可以定義相同的記憶體。

MyUnion2_1 和 MyUnion2_2 分別包含實值類型 (整數) 和字串。在 Managed 程式碼中，實值類型及參考類型不允許重疊。此範例會使用方法多載化來讓呼叫端在呼叫相同 Unmanaged 函式時使用這兩種類型。 MyUnion2_1 配置則是明確的，且具有精確位移值。相反地，MyUnion2_2 具有循序配置，因為對參考類型不允許明確的配置。 MarshalAsAttribute 屬性會將 UnmanagedType 列舉設定為 ByValTStr，這用來識別出現在該等位的 Unmanaged 表示中內嵌固定長度的字元陣列。

NativeMethods 類別包含 TestUnion 和 TestUnion2 方法的原型。 TestUnion2 被多載，以宣告 MyUnion2_1 或 MyUnion2_2 做為參數。

宣告原型

// Declares managed structures instead of unions.
[StructLayout(LayoutKind::Explicit)]
public value struct MyUnion
{
public:
    [FieldOffset(0)]
    int i;
    [FieldOffset(0)]
    double d;
};

[StructLayout(LayoutKind::Explicit, Size = 128)]
public value struct MyUnion2_1
{
public:
    [FieldOffset(0)]
    int i;
};

[StructLayout(LayoutKind::Sequential)]
public value struct MyUnion2_2
{
public:
    [MarshalAs(UnmanagedType::ByValTStr, SizeConst = 128)]
    String^ str;
};

private ref class NativeMethods
{
public:
    // Declares managed prototypes for unmanaged function.
    [DllImport("..\\LIB\\PInvokeLib.dll")]
    static void TestUnion(MyUnion u, int type);

    [DllImport("..\\LIB\\PInvokeLib.dll")]
    static void TestUnion2(MyUnion2_1 u, int type);

    [DllImport("..\\LIB\\PInvokeLib.dll")]
    static void TestUnion2(MyUnion2_2 u, int type);
};

// Declares managed structures instead of unions.
[StructLayout(LayoutKind.Explicit)]
public struct MyUnion
{
    [FieldOffset(0)]
    public int i;
    [FieldOffset(0)]
    public double d;
}

[StructLayout(LayoutKind.Explicit, Size = 128)]
public struct MyUnion2_1
{
    [FieldOffset(0)]
    public int i;
}

[StructLayout(LayoutKind.Sequential)]
public struct MyUnion2_2
{
    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
    public string str;
}

internal static class NativeMethods
{
    // Declares managed prototypes for unmanaged function.
    [DllImport("..\\LIB\\PInvokeLib.dll")]
    internal static extern void TestUnion(MyUnion u, int type);

    [DllImport("..\\LIB\\PInvokeLib.dll")]
    internal static extern void TestUnion2(MyUnion2_1 u, int type);

    [DllImport("..\\LIB\\PInvokeLib.dll")]
    internal static extern void TestUnion2(MyUnion2_2 u, int type);
}

' Declares managed structures instead of unions.
<StructLayout(LayoutKind.Explicit)>
Public Structure MyUnion
    <FieldOffset(0)> Public i As Integer
    <FieldOffset(0)> Public d As Double
End Structure

<StructLayout(LayoutKind.Explicit, Size:=128)>
Public Structure MyUnion2_1
    <FieldOffset(0)> Public i As Integer
End Structure

<StructLayout(LayoutKind.Sequential)>
Public Structure MyUnion2_2
    <MarshalAs(UnmanagedType.ByValTStr, SizeConst:=128)>
    Public str As String
End Structure

Friend Class NativeMethods
    ' Declares managed prototypes for unmanaged function.
    <DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
    Friend Shared Sub TestUnion(
        ByVal u As MyUnion, ByVal type As Integer)
    End Sub

    <DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
    Friend Overloads Shared Sub TestUnion2(
        ByVal u As MyUnion2_1, ByVal type As Integer)
    End Sub

    <DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
    Friend Overloads Shared Sub TestUnion2(
        ByVal u As MyUnion2_2, ByVal type As Integer)
    End Sub
End Class

呼叫函式

public ref class App
{
public:
    static void Main()
    {
        MyUnion mu;// = new MyUnion();
        mu.i = 99;
        NativeMethods::TestUnion(mu, 1);

        mu.d = 99.99;
        NativeMethods::TestUnion(mu, 2);

        MyUnion2_1 mu2_1;// = new MyUnion2_1();
        mu2_1.i = 99;
        NativeMethods::TestUnion2(mu2_1, 1);

        MyUnion2_2 mu2_2;// = new MyUnion2_2();
        mu2_2.str = "*** string ***";
        NativeMethods::TestUnion2(mu2_2, 2);
    }
};

public class App
{
    public static void Main()
    {
        MyUnion mu = new MyUnion();
        mu.i = 99;
        NativeMethods.TestUnion(mu, 1);

        mu.d = 99.99;
        NativeMethods.TestUnion(mu, 2);

        MyUnion2_1 mu2_1 = new MyUnion2_1();
        mu2_1.i = 99;
        NativeMethods.TestUnion2(mu2_1, 1);

        MyUnion2_2 mu2_2 = new MyUnion2_2();
        mu2_2.str = "*** string ***";
        NativeMethods.TestUnion2(mu2_2, 2);
    }
}

Public Class App
    Public Shared Sub Main()
        Dim mu As New MyUnion()
        mu.i = 99
        NativeMethods.TestUnion(mu, 1)

        mu.d = 99.99
        NativeMethods.TestUnion(mu, 2)

        Dim mu2_1 As New MyUnion2_1()
        mu2_1.i = 99
        NativeMethods.TestUnion2(mu2_1, 1)

        Dim mu2_2 As New MyUnion2_2()
        mu2_2.str = "*** string ***"
        NativeMethods.TestUnion2(mu2_2, 2)
    End Sub
End Class

平台範例

在某些情況下，struct 和 union 版面配置可能會根據目標平台而有所不同。例如，在 COM 案例中定義時，請考慮 STRRET 類型：

#include <pshpack8.h> /* Defines the packing of the struct */
typedef struct _STRRET
    {
    UINT uType;
    /* [switch_is][switch_type] */ union
        {
        /* [case()][string] */ LPWSTR pOleStr;
        /* [case()] */ UINT uOffset;
        /* [case()] */ char cStr[ 260 ];
        }  DUMMYUNIONNAME;
    }  STRRET;
#include <poppack.h>

上述 struct 是使用影響類型記憶體配置的 Windows 標頭來宣告。在受控環境定義時，需要這些配置詳細資料，才能與機器碼正確交互操作。

在 32 位元流程，此類型的正確受控定義如下：

[StructLayout(LayoutKind.Explicit, Size = 264)]
public struct STRRET_32
{
    [FieldOffset(0)]
    public uint uType;

    [FieldOffset(4)]
    public IntPtr pOleStr;

    [FieldOffset(4)]
    public uint uOffset;

    [FieldOffset(4)]
    public IntPtr cStr;
}

在 64 位元流程，大小和欄位位移不同。正確的版面配置為：

[StructLayout(LayoutKind.Explicit, Size = 272)]
public struct STRRET_64
{
    [FieldOffset(0)]
    public uint uType;

    [FieldOffset(8)]
    public IntPtr pOleStr;

    [FieldOffset(8)]
    public uint uOffset;

    [FieldOffset(8)]
    public IntPtr cStr;
}

無法在 Interop 案例正確考慮原生配置，可能會導致隨機損毀或更糟的計算。

根據預設，.NET 組件可在 32 位元及 64 位元版本的 .NET 執行階段執行。應用程式必須等到執行階段，才能決定要使用哪一個先前的定義。

下列程式碼片段示範如何在執行階段選擇 32 位元及 64 位元定義之間的範例。

if (IntPtr.Size == 8)
{
    // Use the STRRET_64 definition
}
else
{
    Debug.Assert(IntPtr.Size == 4);
    // Use the STRRET_32 definition
}

SysTime 範例

這個範例示範如何將指向類別的指標傳遞至需要指向結構指標的 Unmanaged 函式。

SysTime 範例會使用下列 Unmanaged 函式，和其原始函式宣告，如下所示：

從 Kernel32.dll 匯出 GetSystemTime。

VOID GetSystemTime(LPSYSTEMTIME lpSystemTime);

傳遞至函式的原始結構包含下列項目：

typedef struct _SYSTEMTIME {
    WORD wYear;
    WORD wMonth;
    WORD wDayOfWeek;
    WORD wDay;
    WORD wHour;
    WORD wMinute;
    WORD wSecond;
    WORD wMilliseconds;
} SYSTEMTIME, *PSYSTEMTIME;

在此範例中，SystemTime 類別包含表示為類別成員原始結構的項目。已設定 StructLayoutAttribute 屬性來確定此成員以其顯示的順序循序排列在記憶體中。

NativeMethods 類別包含 GetSystemTime 方法的 Managed 原型，根據預設會傳遞 SystemTime 類別做為 In/Out 參數。參數必須以 InAttribute 和 OutAttribute 屬性宣告，因為根據預設，會傳遞參考類型的類別做為 In 參數。若要讓呼叫端接收結果，則必須明確地套用這些方向屬性。 App 類別建立 SystemTime 類別的新執行個體，並存取其資料欄位。

程式碼範例

using namespace System;
using namespace System::Runtime::InteropServices;     // For StructLayout, DllImport

[StructLayout(LayoutKind::Sequential)]
public ref class SystemTime
{
public:
    unsigned short year;
    unsigned short month;
    unsigned short weekday;
    unsigned short day;
    unsigned short hour;
    unsigned short minute;
    unsigned short second;
    unsigned short millisecond;
};

public class NativeMethods
{
public:
    // Declares a managed prototype for the unmanaged function using Platform Invoke.
    [DllImport("Kernel32.dll")]
    static void GetSystemTime([In, Out] SystemTime^ st);
};

public class App
{
public:
    static void Main()
    {
        Console::WriteLine("C++/CLI SysTime Sample using Platform Invoke");
        SystemTime^ st = gcnew SystemTime();
        NativeMethods::GetSystemTime(st);
        Console::Write("The Date is: ");
        Console::Write("{0} {1} {2}", st->month, st->day, st->year);
    }
};

int main()
{
    App::Main();
}
// The program produces output similar to the following:
//
// C++/CLI SysTime Sample using Platform Invoke
// The Date is: 3 21 2010

using System;
using System.Runtime.InteropServices;

[StructLayout(LayoutKind.Sequential)]
public class SystemTime
{
    public ushort year;
    public ushort month;
    public ushort weekday;
    public ushort day;
    public ushort hour;
    public ushort minute;
    public ushort second;
    public ushort millisecond;
}

internal static class NativeMethods
{
    // Declares a managed prototype for the unmanaged function using Platform Invoke.
    [DllImport("Kernel32.dll")]
    internal static extern void GetSystemTime([In, Out] SystemTime st);
}

public class App
{
    public static void Main()
    {
        Console.WriteLine("C# SysTime Sample using Platform Invoke");
        SystemTime st = new SystemTime();
        NativeMethods.GetSystemTime(st);
        Console.Write("The Date is: ");
        Console.Write($"{st.month} {st.day} {st.year}");
    }
}

// The program produces output similar to the following:
//
// C# SysTime Sample using Platform Invoke
// The Date is: 3 21 2010

Imports System.Runtime.InteropServices

' Declares a class member for each structure element.
<StructLayout(LayoutKind.Sequential)>
Public Class SystemTime
    Public year As Short
    Public month As Short
    Public weekday As Short
    Public day As Short
    Public hour As Short
    Public minute As Short
    Public second As Short
    Public millisecond As Short
End Class

Friend Class NativeMethods
    ' Declares a managed prototype for the unmanaged function.
    Friend Declare Sub GetSystemTime Lib "Kernel32.dll" (
        <[In](), Out()> ByVal st As SystemTime)
End Class

Public Class App
    Public Shared Sub Main()
        Console.WriteLine("VB .NET SysTime Sample using Platform Invoke")
        Dim st As New SystemTime()
        NativeMethods.GetSystemTime(st)
        Console.Write($"The Date is: {st.month} {st.day} {st.year}")
    End Sub
End Class
' The program produces output similar to the following:
'
' VB .NET SysTime Sample using Platform Invoke
' The Date is: 3 21 2010

OutArrayOfStructs 範例

這個範例顯示如何傳遞包含整數和字串做為 Out 參數的結構陣列至 Unmanaged 函式。

這個範例示範如何藉由使用 Marshal 類別和使用 Unsafe 程式碼來呼叫原生函式。

這個範例使用定義在 PinvokeLib.dll 中的包裝函式和平台叫用，這些也在原始程式檔中提供。它會使用 TestOutArrayOfStructs 函式和 MYSTRSTRUCT2 結構。此結構包含下列項目：

typedef struct _MYSTRSTRUCT2
{
   char* buffer;
   UINT size;
} MYSTRSTRUCT2;

MyStruct 類別包含 ANSI 字元的字串物件。 CharSet 欄位指定 ANSI 格式。 MyUnsafeStruct 為包含 IntPtr 類型的結構，而非字串。

NativeMethods 類別包含 TestOutArrayOfStructs 多載原型方法。如果方法宣告指標做為參數，此類別會以 unsafe 關鍵字標記。因為 Visual Basic 不能使用不安全的程式碼，所以多載的方法、Unsafe 修飾詞和 MyUnsafeStruct 結構是不必要的。

App 類別會實作 UsingMarshaling 方法，該方法會執行所有用來傳遞陣列的必要工作。該陣列以 out (在 Visual Basic 中為ByRef) 關鍵字標記，表示該資料從被呼叫端傳遞至呼叫端。此實作會使用下列 Marshal 類別方法：

PtrToStructure 從 Unmanaged 緩衝區封送處理資料至 Managed 物件。
DestroyStructure 用來釋放在結構中為字串保留的記憶體。
FreeCoTaskMem 用來釋放為陣列保留的記憶體。

如先前所述，C# 允許不安全的程式碼，而 Visual Basic 則否。在 C# 範例中， UsingUnsafePointer 是一種替代的方法實作，會使用指標，而非 Marshal 類別，以傳回包含 MyUnsafeStruct 結構的陣列。

宣告原型

// Declares a class member for each structure element.
[StructLayout(LayoutKind::Sequential, CharSet = CharSet::Ansi)]
public ref class MyStruct
{
public:
    String^ buffer;
    int size;
};

// Declares a structure with a pointer.
[StructLayout(LayoutKind::Sequential)]
public value struct MyUnsafeStruct
{
public:
    IntPtr buffer;
    int size;
};

private ref class NativeMethods
{
public:
    // Declares managed prototypes for the unmanaged function.
    [DllImport("..\\LIB\\PInvokeLib.dll")]
    static void TestOutArrayOfStructs(int% size, IntPtr% outArray);

    [DllImport("..\\LIB\\PInvokeLib.dll")]
    static void TestOutArrayOfStructs(int% size, MyUnsafeStruct** outArray);
};

// 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;
}

internal static unsafe class NativeMethods
{
    // Declares managed prototypes for the unmanaged function.
    [DllImport("..\\LIB\\PInvokeLib.dll")]
    internal static extern void TestOutArrayOfStructs(
        out int size, out IntPtr outArray);

    [DllImport("..\\LIB\\PInvokeLib.dll")]
    internal static extern void TestOutArrayOfStructs(
        out int size, MyUnsafeStruct** outArray);
}

' 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

Friend Class NativeMethods
    ' Declares a managed prototype for the unmanaged function.
    <DllImport("..\LIB\PinvokeLib.dll", CallingConvention:=CallingConvention.Cdecl)>
    Friend Shared Sub TestOutArrayOfStructs(
        ByRef arrSize As Integer, ByRef outArray As IntPtr)
    End Sub
End Class

呼叫函式

public ref class App
{
public:
    static void Main()
    {
        Console::WriteLine("\nUsing marshal class\n");
        UsingMarshaling();
        Console::WriteLine("\nUsing unsafe code\n");
        UsingUnsafePointer();
    }

    static void UsingMarshaling()
    {
        int size;
        IntPtr outArray;

        NativeMethods::TestOutArrayOfStructs(size, outArray);
        array<MyStruct^>^ manArray = gcnew array<MyStruct^>(size);
        IntPtr current = outArray;
        for (int i = 0; i < size; i++)
        {
            manArray[i] = gcnew MyStruct();
            Marshal::PtrToStructure(current, manArray[i]);

            Marshal::DestroyStructure(current, MyStruct::typeid);
            //current = (IntPtr)((long)current + Marshal::SizeOf(manArray[i]));
            current = current + Marshal::SizeOf(manArray[i]);

            Console::WriteLine("Element {0}: {1} {2}", i, manArray[i]->buffer,
                manArray[i]->size);
        }
        Marshal::FreeCoTaskMem(outArray);
    }

    static void UsingUnsafePointer()
    {
        int size;
        MyUnsafeStruct* pResult;

        NativeMethods::TestOutArrayOfStructs(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);
    }
};

public class App
{
    public static void Main()
    {
        Console.WriteLine("\nUsing marshal class\n");
        UsingMarshaling();
        Console.WriteLine("\nUsing unsafe code\n");
        UsingUnsafePointer();
    }

    public static void UsingMarshaling()
    {
        int size;
        IntPtr outArray;

        NativeMethods.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 UsingUnsafePointer()
    {
        int size;
        MyUnsafeStruct* pResult;

        NativeMethods.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);
    }
}

Public Class App
    Public Shared Sub Main()
        Console.WriteLine(vbNewLine + "Using marshal class" + vbNewLine)
        UsingMarshaling()
        'Visual Basic 2005 cannot use unsafe code.
    End Sub

    Public Shared Sub UsingMarshaling()
        Dim arrSize As Integer
        Dim outArray As IntPtr

        NativeMethods.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
End Class

共用方式為

封送處理類別、結構和等位

結構範例

宣告原型

呼叫函式

FindFile 範例

宣告原型

呼叫函式

等位範例

宣告原型

呼叫函式

平台範例

SysTime 範例

程式碼範例

OutArrayOfStructs 範例

宣告原型

呼叫函式

另請參閱

其他資源