c# - 使用 PInvoke 返回包含 char[] 结构的结构数组

Question

我有一个从 PInvoke 返回的结构数组，如果该结构只包含 int 或 float，它会返回数组，但是当我尝试返回一个 char 数组时，它开始变得困惑，我尝试返回一个IntPtr，但这还没有成功。我有什么想法可以使它正常工作吗？

C代码

struct  return_part {
    int partid;
    int numcomp;
    int parttype;
    char partname[100];
};

extern int return_parts(return_part ** array, int * arraySizeInElements) {
    int partcount = 0;
    struct list_part *currentnode; 
    currentnode = head;
    struct section_list *section;
    struct return_part *temppart;

    while (currentnode != NULL) {
        partcount++;
        currentnode = currentnode->next;
    }

    currentnode = head;
    *arraySizeInElements = partcount;

    int bytesToAlloc = sizeof(return_part) * (*arraySizeInElements);
    return_part * a = static_cast<return_part *>(CoTaskMemAlloc(bytesToAlloc));
    *array = a;

    int q = 0;
    while (currentnode != NULL) {
        struct return_part tmp;
        tmp.partid = currentnode->partid;
        tmp.numcomp = currentnode->numcomp;
        strcpy(tmp.partname, currentnode->partname);
        tmp.parttype = currentnode->parttype;

        a[q] = tmp;
        q++;
        currentnode = currentnode->next;
    }

    return 0;
}

C#代码

[StructLayout(LayoutKind.Sequential)]
public struct return_part {
    public int partid;
    public int numcomp;
    public int parttype;
    public char partname;
};

internal static class UnsafeNativeMethods
{
    [DllImport(_dllLocation, CallingConvention = CallingConvention.Cdecl)]
    public static extern int return_parts([MarshalAs(UnmanagedType.LPArray,
    SizeParamIndex = 1)] out return_part[] array, out int arraySizeInElements);
}

public static ReturnPoint[] getpoints(int partid) {
    return_parts[] parts;
    int size;
    int result = UnsafeNativeMethods.return_parts(out parts, out size)
}

Answer 1

对于非托管代码而言，字符数组只是一个字符串，因此您在这里有两个选择。使用哪一个取决于当字符数据返回 C# 时您实际需要如何使用它:

1. 将其编码为数组。参见 this article关于如何编码嵌入到结构中的数组(编辑:这需要是 ByValArray，而不是我最初指出的 LPArray；谢谢@Hans):

   [StructLayout(LayoutKind.Sequential)]
   public struct return_part {
       public int partid;
       public int numcomp;
       public int parttype;
       [MarshalAs(UnmanagedType.ByValArray, SizeConst=100)]
       public char[] partname;
   };
   

2. 将其编码为字符串。参见 this article了解如何编码结构中包含的字符串。

   [StructLayout(LayoutKind.Sequential)]
   public struct return_part {
     public int partid;
     public int numcomp;
     public int parttype;
     [MarshalAs(UnmanagedType.ByValTStr, SizeConst=100)]
     public string partname;
   };