从C ++ DLL调用delphi应用程序中的函数

Question

I have a network management dll written in C++ with wrapper functions in C which requires a procedure from the accompanying Delphi app to send data over the network.

I am passing a function pointer to the C++ dll so that it can call the procedure in the delphi app.

Here's what I thought would work but resulted in an EAV in the dll:-

Delphi Part:

unit NetMgrWrapper;

interface

uses System.Classes;

type

TNetMgrSendData =
procedure ( AUID, ASize: Integer; ABuffer: Pointer ) of object;

TNetMgr = class ( TObject )
private
  fNetworkManager : Pointer;
public
  constructor Create ( const AOnSendData: TNetMgrSendData );
  destructor  Destroy; override;
end;

implementation

const
  DLL_NAME = 'NetMgr.dll';

function  CreateNetMgr ( APtrToSendData: Pointer ): Pointer; cdecl; external DLL_NAME;
procedure FreeNetMgr ( ANetMgr: Pointer ); cdecl; external DLL_NAME;

constructor TNetMgr.Create ( const AOnSendData: TNetMgrSendData );
begin
  fNetworkManager := CreateNetMgr ( @AOnSendData );
end;

destructor TNetMgr.Destroy;
begin
  FreeNetMgr ( fNetworkManager );
end;
end.

C++ Part

#include "cbase.h"
#include "buffer.h"
#include "INatMgr.h"

class NetMgr : public INetManager
{
   private:
     void (*ExternalSendData) (int, int, void *);
   public
     NetMgr ( void (*PtrToSendData) (int,int,void *) )
     {
       ExternalSendData = PtrToSendData;
     } 
     virtual void SendData ( int uid, const CBuffer &payload )
     {
       CBuffer Packet;
       Packet = payload;
       Packet.ResetPtr ();
       ExternalSendNATData ( uid, Packet.LengthBuffer(), Packet.Ptr() );
     }
}

DLL_EXPORT NetMgr CreateNetMgr ( void(*APtrToSendData)(int,int,void *) )
{
  return new NetMgr ( APtrToSendData );
}

DLL_EXPORT void FreeNetMgr ( NetMgr *pNetMgr )
{
  delete pNetMgr;
}

Answer 1

The C++ function receives a function pointer of type

void(*APtrToSendData)(int,int,void *)

But your Delphi code passes this:

procedure ( AUID, AType, ASize: Integer; ABuffer: Pointer ) of object;

This is simply not compatible. The Delphi procedural type has an extra parameter, uses the register calling convention, and is a method of object.

You need to declare TNetMgrSendData as follows:

TNetMgrSendData = procedure(uid, len: Integer; buffer: Pointer); cdecl;

You make life hard for yourself when you declared CreateNetMgr to receive an untyped pointer. It would be much better to declare it like this:

function CreateNetMgr(APtrToSendData: TNetMgrSendData): Pointer; cdecl; 
  external DLL_NAME;

Then you can also refrain from using the @ operator when you call it.