Calling function in C dll from C# which returns somekind of pointer to function pointer

Question

I have an dll written in C (no access to the source code) which I wish to call from C#. If the dll used simple types I would know how to handle it via PInvoke, but it doesn't :(

The function in the dll I'm trying to call takes no parameters so the problem is how to handle the return. I have some example C code which calls the function which I liked to recreate in C#. As I understand it the return type is a pointer to a function pointer, is this correct? The return from the function should also later be passed back to other functions in the dll.

Any help is greatly appreciated :)

/* C code */
typedef const struct simModel* (*ModelFunc)(void);
int ret=0;
HINSTANCE hInst = 0;
ModelFunc f=0;
const struct simModel*model =0;
if (!(hInst=LoadLibrary("model.dll"))) {
    return 1;
}
if (!(f=(ModelFunc)GetProcAddress(hInst,"simModelFunctions"))) {
    ret=1;
} else if (!(model=f())) {
    ret=1;
} else {
    /* Do stuff */
}

Answer 1

The simModelFunctions function returns a pointer to simModel structure (a data type).

The code you show calls the function by finding its address dynamically, which is why it has a function pointer. This pointer does not come from the function itself.

In C# you can simply declare it with DllImport from model.dll. Eg

[DllImport("model.dll", CallingConvention = CallingConvention.Cdecl, ExactSpelling = true)]
private static IntPtr simModelFunctions();

Then you can use Marshal.PtrToStructure if you need to examine the contents of the structure, or just pass the returned IntPtr to other functions without bothering what's inside.