无效的托管/非托管类型组合与嵌入式动态分配的阵列 [英] Invalid Managed/Unmanaged Type Combination With Embedded, Dynamically-Allocated Array

问题描述

我在非托管Win32 C ++ DLL中有一个通用的构造:

I have a common construct in an unmanaged Win32 C++ DLL:

// FirstElemPtrContainer.h
#include "stdafx.h"

typedef unsigned char elem_type; // a byte

typedef struct FirstElemPtrContainer {
    unsigned char num_elems;
    void *allocd_ary;
} FirstElemPtrContainer;

该结构中的void *旨在包含一个指向已分配字节数组的第一个元素的指针.

The void* in the struct is meant to contain a pointer to the first element of an allocated byte array.

使用此定义的DLL然后导出函数来分配，填充和取消分配结构:

The DLL that uses this definition then exports functions to allocate, populate, and deallocate the struct:

// The exported allocator function.
extern "C" _declspec(dllexport) 
    FirstElemPtrContainer *BuildStruct(int elem_count)
{
    FirstElemPtrContainer *fepc_ptr = new FirstElemPtrContainer;
    fepc_ptr->num_elems = elem_count;
    elem_type *ary = new elem_type[fepc_ptr->num_elems];
    for (int i = 0; i < fepc_ptr->num_elems; i++)
    {
        ary[i] = ((i + 1) * 5); // multiples of 5
    }
    fepc_ptr->allocd_ary = ary;

    return fepc_ptr;
}

// The exported deallocator function.
extern "C" _declspec(dllexport) void 
    DestroyStruct(FirstElemPtrContainer *fepc_ptr)
{
    delete[] fepc_ptr->allocd_ary;
    delete fepc_ptr;
}

这些功能对于本机呼叫者来说很好.

These work just fine for a native caller.

在C#中，我尝试通过PInvoke描述相同的结构:

In C#, I try to describe this same structure via PInvoke:

[StructLayout(LayoutKind.Sequential)]
public struct FirstElemPtrContainer
{
    public byte num_elems;
    [MarshalAs(UnmanagedType.LPArray, 
        ArraySubType = UnmanagedType.U1, SizeConst = 4)]
    public IntPtr allocd_ary;
}

...并像这样描述通话界面:

... and describe the call interface like so:

public static class Imports
{
    [DllImport("MyLib", CallingConvention = CallingConvention.Winapi)]
    public static extern IntPtr BuildStruct(int elem_count);

    [DllImport("MyLib", CallingConvention = CallingConvention.Winapi)]
    public static extern void DestroyStruct(IntPtr fepc_ptr);
}

现在我尝试调用我的界面:

Now I attempt to call my interface:

class Program
{
    const int NUM_ELEMS = 4;
    static void Main(string[] args)
    {
        IntPtr fepc_ptr = Imports.BuildStruct(NUM_ELEMS);
        if ( fepc_ptr == IntPtr.Zero ) 
        {
            Console.WriteLine("Error getting struct from PInvoke.");
            return;
        }

        FirstElemPtrContainer fepc =
            (FirstElemPtrContainer)Marshal.PtrToStructure(fepc_ptr, 
        typeof(FirstElemPtrContainer));
        //...
    }
}

PtrToStructure()调用给出错误无法整理类型为'MyLibInvoke.FirstElemPtrContainer'的字段'allocd_ary':无效的托管/非托管类型组合(Int/UInt必须与SysInt或SysUInt配对)."

The PtrToStructure() call gives the error "Cannot marshal field 'allocd_ary' of type 'MyLibInvoke.FirstElemPtrContainer': Invalid managed/unmanaged type combination (Int/UInt must be paired with SysInt or SysUInt)."

您会看到我已经对特定数量的元素进行了硬编码，我们假设调用者坚持使用.我也添加了一个ArraySubType子句，尽管似乎没有什么不同.为什么类型不匹配投诉?

You can see that I've hard-coded a particular number of elements, which we'll assume the caller adheres to. I've also added an ArraySubType clause, though it seems not to make a difference. Why the type mismatch complaint?

推荐答案

您的结构应这样声明:

[StructLayout(LayoutKind.Sequential)]
public struct FirstElemPtrContainer
{
    public byte num_elems;
    public IntPtr allocd_ary;
}

必须这样做，因为 allocd_ary 是指向非托管内存的指针，并且不能由p/invoke编组器进行编组.

it has to be done this way because allocd_ary is a pointer to unmanaged memory and cannot be marshalled by the p/invoke marshaller.

为了阅读 allocd_ary 的内容，您可以使用

In order to read the contents of allocd_ary you can use Marshal.Copy.

FirstElemPtrContainer fepc = (FirstElemPtrContainer)Marshal.
    PtrToStructure(fepc_ptr, typeof(FirstElemPtrContainer));
byte[] ary = new byte[fepc.num_elems];
Marshal.Copy(fepc.allocd_ary, ary, 0, ary.Length);

我怀疑 CallingConvention.Winapi 是错误的，您应该使用 CallingConvention.Cdecl .

I suspect that CallingConvention.Winapi is wrong and that you should be using CallingConvention.Cdecl.

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