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

You need to specify the calling convention, which in this case is cdecl:

TMyFunction = function(X, Y: Integer): Integer; cdecl;

Your code uses the default Delphi calling convention which is register and passes parameters through registers. The cdecl calling convention passes parameters on the stack and so this mis-match explains why communications between the two modules fail.

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Some more comments:

The failure mode for LoadLibrary is to return NULL, that is 0. Check that rather than the return value being >=32.

It's simpler to use implicit linking to import this function. Replace all the LoadLibrary and GetProcAddress code with this simple declaration:

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

The system loader will resolve this import when your executable starts so you don't have to worry about the details of linking.