Using functions from a C++ .DLL within Delphi

I am trying to access various functions from the 'Approximate nearest neighbor' (ANN) library from within Delphi (actually, it is Lazarus/FreePascal, but that shouldn't matter much).

Here is the deceleration in C++:

#include <cstdlib>                      // C standard lib defs
#include <ANN/ANNx.h>                   // all ANN includes
#include <ANN/ANNperf.h>                // ANN performance 

using namespace std;                    // make std:: accessible
....
....
void annMaxPtsVisit(            // set limit on max. pts to visit in search
    int                 maxPts)         // the limit
{
    ANNmaxPtsVisited = maxPts;
}

And here is my attempt to access the annMaxPtsVisit function from within Lazarus (pretend its delphi if you don't know what Lazarus is):

unit unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls;
type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
    procedure annMaxPtsVisit(input:Integer); stdcall;
  private

    { private declarations }
  public
    { public declarations }

  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}
{ TForm1 }
procedure TForm1.annMaxPtsVisit(input: Integer); stdcall; external 'ANN.dll' name 'annMaxPtsVisit';

procedure TForm1.Button1Click(Sender: TObject);
begin
           annMaxPtsVisit(10);
end;

end.

The program compiles, but when I attempt to execute it I get an error message:

"The procedure entry point annMaxPtsVisit could not be located in the dynamic link library ANN.dll"

If anyone could help me out with this I would really appreciate it.

Here are the exports from the DLL:

class ANNsampStat ann_average_err   
class ANNsampStat ann_rank_err  
const ANNbd_tree::`vftable' 
const ANNbruteForce::`vftable'  
const ANNkd_tree::`vftable' 
const ANNpointSet::`vftable'    
double * * __cdecl annAllocPts(int,int) 
double * __cdecl annAllocPt(int,double) 
double * __cdecl annCopyPt(int,double *)    
double __cdecl annDist(int,double *,double *)   
protected: void __thiscall ANNkd_tree::SkeletonTree(int,int,int,double * *,int *)   
public: __thiscall ANNbd_tree::ANNbd_tree(class ANNbd_tree const &) 
public: __thiscall ANNbd_tree::ANNbd_tree(class std::basic_istream<char,struct std::char_traits<char> > &)  
public: __thiscall ANNbd_tree::ANNbd_tree(double * *,int,int,int,enum ANNsplitRule,enum ANNshrinkRule)  
public: __thiscall ANNbd_tree::ANNbd_tree(int,int,int)  
public: __thiscall ANNbruteForce::ANNbruteForce(class ANNbruteForce const &)    
public: __thiscall ANNbruteForce::ANNbruteForce(double * *,int,int) 
public: __thiscall ANNkd_tree::ANNkd_tree(class ANNkd_tree const &) 
public: __thiscall ANNkd_tree::ANNkd_tree(class std::basic_istream<char,struct std::char_traits<char> > &)  
public: __thiscall ANNkd_tree::ANNkd_tree(double * *,int,int,int,enum ANNsplitRule) 
public: __thiscall ANNkd_tree::ANNkd_tree(int,int,int)  
public: __thiscall ANNpointSet::ANNpointSet(class ANNpointSet const &)  
public: __thiscall ANNpointSet::ANNpointSet(void)   
public: __thiscall ANNsampStat::ANNsampStat(void)   
public: class ANNbd_tree & __thiscall ANNbd_tree::operator=(class ANNbd_tree const &)   
public: class ANNbruteForce & __thiscall ANNbruteForce::operator=(class ANNbruteForce const &)  
public: class ANNkd_tree & __thiscall ANNkd_tree::operator=(class ANNkd_tree const &)   
public: class ANNpointSet & __thiscall ANNpointSet::operator=(class ANNpointSet const &)    
public: class ANNsampStat & __thiscall ANNsampStat::operator=(class ANNsampStat const &)    
public: double __thiscall ANNsampStat::max(void)    
public: double __thiscall ANNsampStat::mean(void)   
public: double __thiscall ANNsampStat::min(void)    
public: double __thiscall ANNsampStat::stdDev(void) 
public: int __thiscall ANNsampStat::samples(void)   
public: virtual __this开发者_Go百科call ANNbd_tree::~ANNbd_tree(void)    
public: virtual __thiscall ANNbruteForce::~ANNbruteForce(void)  
public: virtual __thiscall ANNkd_tree::~ANNkd_tree(void)    
public: virtual __thiscall ANNpointSet::~ANNpointSet(void)  
public: virtual double * * __thiscall ANNbruteForce::thePoints(void)    
public: virtual double * * __thiscall ANNkd_tree::thePoints(void)   
public: virtual int __thiscall ANNbruteForce::annkFRSearch(double *,double,int,int *,double *,double)   
public: virtual int __thiscall ANNbruteForce::nPoints(void) 
public: virtual int __thiscall ANNbruteForce::theDim(void)  
public: virtual int __thiscall ANNkd_tree::annkFRSearch(double *,double,int,int *,double *,double)  
public: virtual int __thiscall ANNkd_tree::nPoints(void)    
public: virtual int __thiscall ANNkd_tree::theDim(void) 
public: virtual void __thiscall ANNbruteForce::annkSearch(double *,int,int *,double *,double)   
public: virtual void __thiscall ANNkd_tree::annkSearch(double *,int,int *,double *,double)  
public: virtual void __thiscall ANNkd_tree::Dump(enum ANNbool,class std::basic_ostream<char,struct std::char_traits<char> > &)  
public: virtual void __thiscall ANNkd_tree::getStats(class ANNkdStats &)    
public: virtual void __thiscall ANNkd_tree::Print(enum ANNbool,class std::basic_ostream<char,struct std::char_traits<char> > &) 
public: void __thiscall ANNkd_tree::`default constructor closure'(void) 
public: void __thiscall ANNkd_tree::annkPriSearch(double *,int,int *,double *,double)   
public: void __thiscall ANNsampStat::operator+=(double) 
public: void __thiscall ANNsampStat::reset(void)    
void __cdecl annClose(void) 
void __cdecl annDeallocPt(double * &)   
void __cdecl annDeallocPts(double * * &)    
void __cdecl annMaxPtsVisit(int)    
void __cdecl annPrintStats(enum ANNbool)    
void __cdecl annResetCounts(void)   
void __cdecl annResetStats(int) 
void __cdecl annUpdateStats(void)   

Maybe importing by index works:

procedure annMaxPtsVisit(input: Integer); stdcall; external 'ANN.dll' index 39;

(That's the index gotten via Dependecy Walker)

And you might have to change to cdecl calling convention, depending on how the DLL was built:

procedure annMaxPtsVisit(input: Integer); cdecl; external 'ANN.dll' index 39; // could work

Edit: Looks like cdecl is the right thing to do, looking at your added exports.

Edit2: Dependency walker shows also the decorated names, as @user786653 suspected. This also seems to work:

procedure annMaxPtsVisit(input: Integer); cdecl; external 'ANN.dll' Name '?annMaxPtsVisit@@YAXH@Z';

Looks ugly, though.

First of all declare annMaxPtsVisit as ordinary procedure, not a TForm1 method:

procedure annMaxPtsVisit(input: Integer); stdcall; external 'ANN.dll';