visual studio 2010 - can't pass C# int to unmanaged C++ DLL -

i new interfacing c# .exe project native visual-c++ dll.

i can't figure out how pass simple integer, , following code results in popup error "pinvoke ... unbalanced stack".

c++ dll...........

 extern "c"  {  __declspec(dllexport) void start_frame_generation(  int& test_num ) {     console::writeline ("test_num = " + test_num );     } 

c# .......................

    [dllimport("ultrasound_frame_grabber.dll")] public static extern void start_frame_generation(  ref int test_num );      private void vnguideviewform_load(object sender, eventargs e)     {              int test_num = 123;             start_frame_generation( ref test_num);      } 

you need add callingconvention = callingconvention.cdecl dllimport so:

[dllimport("ultrasound_frame_grabber.dll", callingconvention = callingconvention.cdecl)]

omitting declaration cause unbalanced stack message seeing.

compilers before vs2010 assumed callingconvention.cdecl since had add unless calling 1 of win32 apis.