CODEWITHSUNDEEP
c#pinvoke
Sergey
Sergey

Reputation: 11908

PInvoke problem

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?

Upvotes: 1

Views: 432

Answers (2)

agent-j
agent-j

Reputation: 27913

I don't think an array is what you're looking for. It's a pointer to the size of the array, not a pointer to an array of sizes. Try this:

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

byte[] arrayIn= Encoding.UTF8.GetBytes(source);

uint arrayInSize = (uint)arrayIn.Length;
byte[] arrayOut = new byte[100];
uint arrayOutSize = (uint)arrayOut.Length; 
CreateCert2WithArrays (arrayIn, (uint) arrayIn.Length, arrayOut, ref arrayOutSize);
uint[] arrayOutSize = new uint[1];
arrayOut = new byte[(int)arrayOut];
CreateCert2WithArrays (arrayIn, (uint) arrayIn.Length, arrayOut, ref arrayOutSize);

Upvotes: 0

David Heffernan
David Heffernan

Reputation: 612794

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.

Upvotes: 4

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