Question

This is the signature of the native c method:

bool nativeMethod1
(unsigned char *arrayIn,
unsigned int arrayInSize,
unsigned char *arrayOut,
unsigned int *arrayOutSize);

I have no idea why arrayOutSize is a pointer to unsigned int but not int itself.

This is how I invoke it from C#:

byte[] arrayIn= Encoding.UTF8.GetBytes(source);
uint arrayInSize = (uint)arrayIn.Length;
byte[] arrayOut = new byte[100];
uint[] arrayOutSize = new uint[1];
arrayOutSize[0] = (uint)arrayOut.Length;

fixed (byte* ptrIn = arrayIn, ptrOut = arrayOut)
{
    if (nativeMethod1(ptrIn, arrayInSize, ptrOut, arrayOutSize))
    {
        Console.WriteLine("True");
    }
    else
    {
        Console.WriteLine("False");
    }
}

and some DllImport code

[DllImport(@"IcaCert.dll", EntryPoint = "CreateCert2", CallingConvention = CallingConvention.Cdecl)]<br>
public unsafe static extern bool CreateCert2WithArrays(
        byte* data, uint dataSize,<br>
        byte* result, uint[] resultSize);

According to the documentation, native method should return arrayOut fulfilled with the values depending on arrayIn. If its size is less than needed, it returns false. True otherwise. I figured that it’s needed 850 elements in arrayOut. So, when I create new byte[100] array, function should return false, but it always returns true. WHY?

Answer 1

You don’t need unsafe code and fixed here. The standard P/Invoke marshaller is more than up to the task:

[DllImport(@"IcaCert.dll", EntryPoint = "CreateCert2", CallingConvention = CallingConvention.Cdecl)]
public static extern bool CreateCert2WithArrays(
    byte[] arrayIn, 
    uint arrayInSize,
    byte[] arrayOut,
    ref uint arrayOutSize
);

byte[] arrayIn = Encoding.UTF8.GetBytes(source);
uint arrayInSize = (uint)arrayIn.Length;
uint arrayOutSize = 0;

CreateCert2WithArrays(arrayIn, arrayInSize, null, ref arrayOutSize);
byte[] arrayOut = new byte[arrayOutSize];
CreateCert2WithArrays(arrayIn, arrayInSize, arrayOut, ref arrayOutSize);

I don’t know for sure what the protocol of the function is, but it is normal for such functions to be able to receive NULL if the output array has size 0.