c# - PInvoke一个结构指针来获取数据

Question

C 代码:

// Device description structure
struct DeviceInfo
{
  unsigned short deviceID;
  unsigned short productID;
  unsigned short versionNumber;
  wchar_t* deviceName;
}; 

void __cdecl GetAttachedDevices(
  int* count,
  DeviceInfo* deviceInfoList
);

和 PInvoke C# 代码以使用此 C DLL:

    public struct DeviceInfo
    {
        public ushort deviceID;
        public ushort productID;
        public ushort versionNumber;
        public IntPtr deviceName;
    }; 

    [DllImport("Native.dll", CallingConvention=CallingConvention.Cdecl)]
    public static extern void GetAttachedDevices(ref int count, ref DeviceInfo deviceInfoList);

当我使用此 C# 代码时:

    int count = 0;
    DeviceInfo dev = new DeviceInfo();

    GetAttachedDevices(ref count, ref dev);

我在 dev 中只获得一个设备信息(当 count 中有 2 个设备时)。

我应该怎么做才能获取所有设备数据？

Answer 1

您需要分配并传递一个数组。像这样声明函数:

[DllImport("Native.dll", CallingConvention=CallingConvention.Cdecl)]
public static extern void GetAttachedDevices(
    ref int count, 
    [In, Out] DeviceInfo[] deviceInfoList
);

这样调用它:

int count = 16; // not sure how you are expected to come up with this value
DeviceInfo[] dev = new DeviceInfo[count];

GetAttachedDevices(ref count, dev);

如何分配数组？也许该函数允许您为数组传递一个空指针以获得所需的大小。在这种情况下，您有:

int count = 0;
GetAttachedDevices(ref count, null);
DeviceInfo[] dev = new DeviceInfo[count];
GetAttachedDevices(ref count, dev);

您将能够从 C 代码或其文档中计算出这些细节。