Reference a GNU C DLL built in GCC against Cygwin, from C#/NET
- by Dale Halliwell
Here is what I want: I have a huge legacy C/C++ codebase written for POSIX, including some very POSIX specific stuff like pthreads. This can be compiled on Cygwin/GCC and run as an executable under Windows with the Cygwin DLL.
What I would like to do is build the codebase itself into a Windows DLL that I can then reference from C# and write a wrapper around it to access some parts of it programatically.
I have tried this approach with the very simple "hello world" example at http://www.cygwin.com/cygwin-ug-net/dll.html and it doesn't seem to work.
#include <stdio.h>
extern "C" __declspec(dllexport) int hello();
int hello()
{
printf ("Hello World!\n");
return 42;
}
I believe I should be able to reference a DLL built with the above code in C# using something like:
[DllImport("kernel32.dll")]
public static extern IntPtr LoadLibrary(string dllToLoad);
[DllImport("kernel32.dll")]
public static extern IntPtr GetProcAddress(IntPtr hModule, string procedureName);
[DllImport("kernel32.dll")]
public static extern bool FreeLibrary(IntPtr hModule);
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
private delegate int hello();
static void Main(string[] args)
{
var path = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "helloworld.dll");
IntPtr pDll = LoadLibrary(path);
IntPtr pAddressOfFunctionToCall = GetProcAddress(pDll, "hello");
hello hello = (hello)Marshal.GetDelegateForFunctionPointer(
pAddressOfFunctionToCall,
typeof(hello));
int theResult = hello();
Console.WriteLine(theResult.ToString());
bool result = FreeLibrary(pDll);
Console.ReadKey();
}
But this approach doesn't seem to work. LoadLibrary returns null. It can find the DLL (helloworld.dll), it is just like it can't load it or find the exported function.
I am sure that if I get this basic case working I can reference the rest of my codebase in this way. Any suggestions or pointers, or does anyone know if what I want is even possible? Thanks.
