为什么那些 WinAPI 签名有效而其他签名无效？

问题描述

我发现了一些关于通过 DllImport 从 C# 调用 WinAPI 函数的问题，我无法理解。所以，最初我使用功能 SetConsoleCursorPosition，但我认为这个问题比一个具体的函数更广泛。但这是一个很好的例子。它的非托管签名看起来像：

BOOL WINAPI SetConsoleCursorPosition(  _In_ HANDLE hConsoleOutput,_In_ SomeStruct  dwCursorPosition);

SomeStruct 在哪里：

typedef struct _SomeStrcut { SHORT a; SHORT b; } SomeStruct;

在 C# 中：

[DllImport("kernel32.dll",EntryPoint="SetConsoleCursorPosition",SetLastError = true)]
public static extern bool SetData(IntPtr screenHandle,SomeStruct ab);

[StructLayout(LayoutKind.Explicit)] //Sequential always works (size 4 bytes).
public struct SomeStruct
{
    [FieldOffset(0)] public ushort A;

    [FieldOffset(2)]public ushort B;

    public SomeStruct(ushort a,ushort b) { this.A = a; this.B = b; }
}

它工作正常，但我决定用两个 ushort 参数替换 SomeStruct 以提高可用性。两个短整数在 4 个字节中具有相同的大小，就像一个 SomeStruct - 我认为没有区别：

[DllImport("kernel32.dll",EntryPoint = "SetConsoleCursorPosition",ushort a,ushort b);

但是函数通过 GetLastError - ErrorInvalidParameter 导致错误和 87 错误代码。我测试了一些具有不同签名的过期时间，它们让我感到惊讶。使用 int/uint 一切正常：

[DllImport("kernel32.dll",int ab);

低 2 个字节 - a，高 2 个字节 - b。完美。我所有的实验代码：

public static class Question
{
    [DllImport("kernel32.dll")]
    public static extern IntPtr GetStdHandle(int val);

    /// <summary>Initial declaration as in documentation</summary>
    [DllImport("kernel32.dll",SetLastError = true)]
    public static extern bool SetData(IntPtr screenHandle,SomeStruct ab);

    [DllImport("kernel32.dll",int ab);

    [DllImport("kernel32.dll",int ab,int someInt);

    [DllImport("kernel32.dll",ulong ab);

    [DllImport("kernel32.dll",ushort b);

    [DllImport("kernel32.dll",byte b1,byte b2,byte b3,byte b4);

    [DllImport("kernel32.dll",byte b4,uint some);

    [DllImport("kernel32.dll",uint b);

    [StructLayout(LayoutKind.Sequential)]
    public struct SomeStruct
    {
        [FieldOffset(0)] public ushort A;

        [FieldOffset(2)]public ushort B;

        public SomeStruct(ushort a,ushort b) { this.A = a; this.B = b; }
    }

    public static void test()
    {
        IntPtr handle = GetStdHandle(-11); string[] testResults = new string[10]; int i = 0;

        //Test 1: Struct - Works
        testResults[i++] = string.Format("Result: {0} Err: {1}",SetData(handle,new SomeStruct(5,1)),Marshal.GetLastWin32Error());

        //Test 2: int or uint -> Works (lower two bytes - A,upper two bytes - B)
        testResults[i++] = string.Format("Result Int: {0} Err: {1}",5 | (1 << 16)),Marshal.GetLastWin32Error()); Console.Write('I');

        //Test 3: ulong -> Works (lower two bytes - A,next two bytes - B)
        testResults[i++] = string.Format("Result Ulong: {0} Err: {1}",(ulong)(9 | (2 << 16))),Marshal.GetLastWin32Error()); Console.Write('U');

        //Test 4: int/int -> Works (lower two bytes - A,upper two bytes - B),next int - not used at all
        testResults[i++] = string.Format("Result Int/Int: {0} Err: {1}",2 | (3 << 16),2789),Marshal.GetLastWin32Error()); Console.Write("II");

        //Test 5: ushort/ushort -> not works (Error 87 - Invalid Parameter)
        testResults[i++] = string.Format("Result Ushort/Ushort: {0} Err: {1}",(ushort)5,(ushort)1),Marshal.GetLastWin32Error());

        //Test 6: 4 bytes -> not works (Error 87 - Invalid Parameter)
        testResults[i++] = string.Format("Result 4 bytes: {0} Err: {1}",5,1,0),Marshal.GetLastWin32Error());

        //Test 7: 4 bytes and int -> WORKS?? How it works??
        testResults[i++] = string.Format("Result 4 bytes Int: {0} Err: {1}",7 | (4 << 16)),Marshal.GetLastWin32Error()); 
        Console.Write("4bI");

        //Test 8: ushort and uint -> not works
        testResults[i++] = string.Format("Result ushort/uint {0} Err: {1}",(ushort)12897,(uint)(2 | (2 << 16))),Marshal.GetLastWin32Error()); 

        //Printing all results on console
        SetData(handle,new SomeStruct(0,5));
        //Size of SomeStruct: 4 bytes
        Console.WriteLine("SomeStructSize: {0}",Marshal.SizeOf(typeof(SomeStruct)));
        for (int j = 0; j < i; j++) Console.WriteLine(testResults[j]);
    }
}

输出为：

     I
         U
  II
     4bI
SomeStructSize: 4
Result: True Err: 2
Result Int: True Err: 2
Result Ulong: True Err: 0
Result Int/Int: True Err: 0
Result Ushort/Ushort: False Err: 87
Result 4 bytes: False Err: 87
Result 4 bytes Int: True Err: 87
Result ushort/uint False Err: 87

现在我很困惑。我只了解我不了解调用本机代码发生了什么。为什么函数适用于 int/uint 而不适用于 2 ushort 或 4 个字节？？它是如何处理 4 个字节和 int 的，为什么？？？请给我解释一下。谢谢！

解决方法

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c#c#calling-convention marshalling