如何在c#中编组指向固定大小数组的指针

Question

我有一个带有导出函数的 C++ DLL：

__declspec (dllexport) int AllocateBuf(DataBufferIn *in);

该函数分配缓冲区数组并为测试赋值

__declspec (dllexport) int AllocateBuf(DataBufferIn *in){
    for (int i = 0 ; i < 4; i++){
        in->data_r[i] = (double*)VirtualAlloc(
            NULL,                 // System selects address
            1024 * sizeof(double), // Size of allocation
            MEM_RESERVE | MEM_COMMIT, // Allocate reserved pages
            PAGE_READWRITE);       // Protection = no access
        for (int j = 0; j < 128; i++){
            (in->data_r[i])[j] = j;//Assign value for test    
        }
    }

} 

struct DataBufferIn 是这样的

struct DataBufferIn
{
    double* data_r[4];
    double* data_g[4];
};

以下是我的代码，我想在 c# 中编组这个结构，但我得到一个异常(An unhandled exception of type 'System.Runtime.InteropServices.SafeArrayTypeMismatchException' occurred in C_Sharp_Sample.exe) 。 我经常被卡在这个问题上，有人知道如何解决这个问题吗？ 谢谢 ：）

public struct DataBufferIn
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public IntPtr[] data_r;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public IntPtr[] data_g;
};

[DllImport("test.dll", CallingConvention = CallingConvention.Cdecl)]
public static extern int AllocateBuf(ref DataBufferIn _data_buf_in);

private void button_allocate_buf_Click(object sender, EventArgs e)
{
    DataBufferIn data_buf_in = new DataBufferIn();
    AllocateBuf(ref data_buf_in);//<---Function call fail...

    double[] doubleArrayRed = new double[1024];
    Marshal.Copy(data_buf_in.lum_data_r[0], doubleArrayRed, 0, 1024);
    .....
}

Answer 1

根据 Charlieface 的建议，添加 [StructLayout(LayoutKind.Sequential)] 可以解决这个问题。

[StructLayout(LayoutKind.Sequential)]
public struct DataBufferIn
{
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public IntPtr[] data_r;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
    public IntPtr[] data_g;
};