Question

We hired a C programmer to develop a native component for use in a .NET application. We agreed on a conceptual API. I will pass his method two arrays and he will give back an array. I got the code today. Here is the header file. Real names are obscured:

__declspec(dllexport) int NativeMethod(
    struct params * config,
    int c_input_a_rows, 
    struct input_a_row *input_a_rows,
    int c_input_b_rows, 
    struct input_b_row *input_b_rows,
    int c_count, 
    int *p_c_output_rows, 
    struct output_row * output_rows);

struct params
{
    int a;
    int b;
    int c;
    double d;
    double e;
    int f;
    int g;
    char h[1000];
};

struct input_a_row
{
    int a;
    int b;
    double c;
};

struct input_b_row
{
    int a;
    int b;
    int c;
    int d;
    int e;
    double f;
    double g;
};

struct output_row
{
    int a;
    int b;
    int c;
    int d;
    int e;
    int f;
    int g;
    double h;
    double i;
    double j;
};

From this I generated .NET code using P/Invoke Interop Assistant. I was not able to get it to work by opening the DLL. It complained that the file has no assembly manifest. So I plugged the header file into the SigImpl Translate Snipped and got this:

[DllImport("the.dll", EntryPoint="NativeMethod")]
public static extern int NativeMethod(
    ref params config,
    int c_input_a_rows, 
    ref input_a_row input_a_rows,
    int c_input_b_rows, 
    ref input_b_row input_b_rows,
    int c_count, 
    ref int p_c_output_rows, 
    ref output_row output_rows);

It also create all as structs as expected. Each one has a class attribute:

[StructLayout(LayoutKind.Sequential, CharSet = CharSet.Ansi)]

Two questions. Did this code generate correctly? Second, how do I use it? The signature does not have arrays. I know I probably need to use pointers somehow, but how? I don’t expect you to solve this for me, but can you point me to some way to understand how to figure it out without taking a course in low native programming? Thanks!

Answer 1

Okay, after I posted this question I started hacking away again. The first thing I tried worked!

    private static extern int NativeMethod(
        params config,
        input_a_row[] input_a_rows,
        input_b_row[] input_b_rows,
        int count,
        ref output_row[] output_rows);

There’s one other thing I had to do. I was getting an error that entry point was not found. I solved this by using DUMPBIN (from VS console) to find out that the export was actually named ?NativeMethod@@YAHPAUconfig@@HPAUinput_row_a@@HPAUinput_row_b@@HPAHPAUoutput_row@@@Z. How fragile is that?!