C ++ / C＃互操作性类型转换

Question

I am developing a program which uses dll driver file. I successfully linked the dll into my code but have a problem with one method

Dll function:

word NdEnumDevices(const char* const ** devs);

I've linked it to c# like this

[DllImport("NeurobitDrv.dll")]
    public static extern ushort NdEnumDevices(ref string[] devs);

As i don't have much experience with C++ I dont really understand what const char* const ** devs means. I know for sure that this argument receives an array of strings but i only get one element where should be 3

And it Throws out an Access violation Exception

Can someone tell me what type should i use in c#??

---

I've worked around it, just hardcoded string array with device names and it works just fine :D

Answer 1

const char* const ** devs is likely the same as const char* const *devs[] which would be

pointer to 
  an array of
    constant pointers to
      constant characters.

This is most likely caused be the ref (although I'm not too sure about that). A ref to an array of strings could be compiled as a pointer to an array of strings.

As pointed out in this question, you should be safe to use const char* for that.

I think what you could be missing is the length of the array. The function should be declared as

word NdEnumDevices(const char* devs[], unsigned int length);
// C#
[DllImport("NeurobitDrv.dll")]
private static extern ushort NdEnumDevices(string[] devs, UInt32 length);

public static ushort NdEnumDevices(string[] devs) {
    NdEnumDevices(devs, devs.Length); // Delegate for length
}