解读封送类、结构体和联合体实例

// 假设有一个非托管的COM接口IDemoInterface
[ComImport]
[Guid("...")]
interface IDemoInterface {
    void DoSomething();
}

// 定义一个实现该接口的托管类
public class ManagedClass : IDemoInterface {
    public void DoSomething() {
        Console.WriteLine("Doing something...");
    }
}

// 在托管代码中创建并传递给非托管代码
var managedInstance = new ManagedClass();
// 这里假设有一个非托管函数接收IDemoInterface类型的参数
NativeMethods.PassToUnmanaged(managedInstance);

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

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]
public struct MyPerson {
    [MarshalAs(UnmanagedType.LPStr)]
    public string first;
    [MarshalAs(UnmanagedType.LPStr)]
    public string last;
}

[DllImport("PinvokeLib.dll")]
static extern int TestStructInStruct([In] MyPerson2 person2);

// 构建MyPerson实例
var person = new MyPerson { first = "John", last = "Doe" };
// 创建包含person指针的MyPerson2实例
var person2 = new MyPerson2 { person = Marshal.AllocCoTaskMem(Marshal.SizeOf(person)), age = 30 };
// 复制person的内容到分配的非托管内存
Marshal.StructureToPtr(person, person2.person, false);
try {
    // 调用非托管函数
    var result = TestStructInStruct(person2);
} finally {
    // 清理非托管资源
    Marshal.FreeCoTaskMem(person2.person);
}

union MYUNION {
    int i;
    double d;
};

[StructLayout(LayoutKind.Explicit)]
public struct MyUnion {
    [FieldOffset(0)]
    public int i;
    [FieldOffset(0)]
    public double d;
}