Calling functions from a c++ DLL in Delphi

Question

I created a new c++ DLL project in VS2010 that exposes 1 function

#include \"stdafx.h\"    
#define DllImport   extern \"C\" __declspec( dllimport )
#define         


        

Answer 1

On RAD Studio Berlin, using CLANG compiler for the C++ part, a cdecl function which is extern "C" will have its name prepended with an underscore, traditional unix "C" style. The above code doesn't work in this case, but use the name attribute of the external declaration to fix the problem:

function DoMath(X, Y: Integer): Integer; cdecl; external 'exampleDLL.dll' name '_DoMath';

Not tried it with other compilers, so it might be a general issue with cdecl. The Windows API does not use cdecl, but uses same calling convention as Delphi so, for example, the Winapi.Windows declarations of DLL functions do not have the underscore added.

Same true if using GetProcAddress, the correct call is GetProcAddress(hDLL, '_DoMath'); otherwise nil is returned.

Hope this helps anyone struggling to get Delphi talking to C++.