pointer to pointer(C style) to int array(C# style)?

[profactory]

Hi all,

I have to include a C style DLL into C#. The dll has a function which should give me back a string, an array of integer and a single integer.
The DllImport looks like this:

[DllImport("key2.dll", EntryPoint = "#4")]
public static extern bool measureKey(ref StringBuilder msg, int[] Params,byte[] Result,ref int rSize);

The C# source to call the function:

int[] parameter = new int[5];
parameter[0] = 5300;
parameter[1] = 4700;
parameter[2] = 4000;
parameter[3] = 0;
parameter[4] = 80;
StringBuilder msg = new StringBuilder(128);
int rSize = 0;
int[] result = new int[7];
[B]
bool value = measureKey(ref msg, parameter, ref result, ref rSize);[/B]

The value, the msg and the rSize is correct.
Result should contain 7 values greater than 0, but I only get the first one, and the size of the array also changed from 7 to 1.
The first value of result is correct.

I also got the function in C style, here you have to use a pointer to pointer to get the values:

int * Result;
int rSize;
char * Msg;
int Params[EXPECTEDVALUES];
retval = measureKey(&Msg, Params, &Result, &rSize);
if (!retval) {[INDENT]printf("Error: ");
printf(Msg);[/INDENT]
}else{[INDENT]printf("Success: ");
for(y = 0; y < rSize; y++){[/INDENT][INDENT][INDENT]printf("%d  ",Result[y]);[/INDENT][/INDENT][INDENT]}[/INDENT]}
printf(Msg);
free(Result);
}

Can anybody help me how to get the other 6 values of result?

Thanks!
Greetings!

[tlhintoq]

TIP: When you are writing your question, there is a button on the tool bar that wraps the [code] tags around your copy/pasted code. It helps a bunch. Its the button with a '#' on it. More on tags. They're cool. Check'em out.

[GaryTexmo]

I'm not sure about this but hopefully this helps...

I think a C# array is different than a C/C++ array when it comes to pointers; however, you can still access pointers in C#, you just need to use "unsafe" code. Here's some info I found via google.

http://www.softsteel.co.uk/tutorials/cSharp/lesson5.html

Since rSize comes out correctly, you may need to use the alternative pointer notation... it's been a while since I've done this, but I think it's something like...

...
for (byte i = 0; i < rSize; i++)
{
  int val = *(result + i);
  ...
}

But you might want to look into that. For example, I'm not sure if i should be a byte or an int... memory fuzzy... ack! ;) As I said, it's been a while. Hopefully this is more current for you and you know what the heck I'm talking about.

[Plater]

Well your dllimport lists result as a byte[] but you send in a reference to an int[]
int is 32bits, byte is 8. Try correcting that.
Although I would suspect you have to do more fiddling, possibly using IntPtr instead.

[profactory]

Hi all!


first of all thanks for the tips!

I've found a solution by using the unsafe method.

for everyone, who's interested:

        [DllImport("key2.dll", EntryPoint = "#4")]
        unsafe public static extern bool measureKey(ref StringBuilder msg, int[] Params,int** Result,int* rSize);

            int[] result = new int[7];
            unsafe
            {
                int* ptrResult = stackalloc int[7];

                bool value = measureKey(ref msg, parameter, &ptrResult, &rSize);

                for (int i = 0; i < rSize; i++)
                {
                    result[i] = *ptrResult;
                    ptrResult++;
                }

            }

Best regards!