Port this C code to Delphi/Lazarus

Question

I have this code in C that I want to port to Delphi, but i can't make it work.

.CPP CODE

#include <Windows.h>

#include <io.h>
#include <stdio.h>

#include "GLibExp.h"
#pragma comment(lib, "GLib.lib")

void MyCFunc(LPCTSTR GStr)
{
    GFile GVar = NULL;
    GVar = GrfLoad(GStr, 1);
    if ( !GVar )
    {
        printf("Error during loading!\n");
    } else
        printf("All fine!\n");

    GrfFree(GVar);
    system("pause");
}

void main()
{
    CHAR StrG[MAX_PATH] = "Test.grf";
    MyCFunc(StrG);
    return;
}

GLibExp.h

#ifndef GLibExpH
#define GLibExpH

#if defined(GRF_DLL)
#define GEXPORT __declspec(dllexport)
#else
#define GEXPORT extern
#endif

class CGFILE;
typedef CGFILE* GFile;
//typedef void* GFile; //Also works like this

#ifdef __cplusplus
extern "C" {
#endif
GEXPORT GFile GrfLoad(const char *GName, unsigned char Mode = 1);
GEXPORT void GrfFree(GFile GVar);
#ifdef __cplusplus
}
#endif

#endif//GLibExpH

The program calls a DLL at runtime to use the GRFLoad and GRFFree functions. I try to port this to Delphi, but without success.

Delphi/Lazarus Code:

unit Unit1;

{$mode objfpc}{$H+}

interface

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

{$Link GLib.lib}

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { private declarations }
  public
    { public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

function GrfLoad(const fname: PChar; Modo: Boolean): Pointer; cdecl; external 'GLib.dll';

procedure TForm1.Button1Click(Sender: TObject);
var
  PVar: Pointer;
begin
  PVar:= GrfLoad(PChar('test.grf'),false);
end;

end. 

If I comment out the line {$Link GLib.lib}, the program runs, but it always crashes when I call GRFLoad (the program stops working and then closes). If I leave in the {$Link GLib.lib} line, the program don't compile and reports an error:

project1.lpr(20,1) Error: Illegal COFF Magic while reading GLib.lib

Any hints?

NOTE: I just added a link to a Visual C++ 2010 project with all files needed. In fact, I just made a "New project -> Win32 Console Application" (I mark "empty project" in the Wizard), add a new CPP file and paste the code, and change "Properties -> Configuration Properties -> Linker -> Enable Incremental Linking: NO", that all.

https://drive.google.com/open?id=1JxW4Wra_kT8gfBda1t0WWqagzazzQVne

Answer 1

The proper declaration of the functions would be using a PAnsiChar (char is always a single byte type in C and C++):

type
  GFile = Pointer; // alternatively: GFile = THandle;

function GrfLoad(const FName: PAnsiChar; Mode: Boolean): GFile; cdecl; external 'GLib.dll' name 'GrfLoad';
procedure grfFree(GVar: GFile); cdecl; external 'GLib.dll' name 'GrfFree';

But it is well possible that the exported names are not GrfLoad and GrfFree, but different names, e.g. _GrfLoad and _GrfFree. You can find out which names are actually exported using a tool like MS's Dependency Walker or using Delphi's own TDump.exe (look for Exports section), i.e. using

tdump glib.dll

on the command line in the directory where glib.dll resides.

If the names differ, then you'll have to change the name parts of the external declaration, for instance external 'Glib.dll' name '_GrfLoad';, etc.

Some more info in my article: Pitfalls of converting.

Of course it is also possible that the DLL can't find another DLL it is dependent on. Dependency Walker will also tell you about missing imports.

Update

Note that the DLL in the zip file to which you linked is called GrfLib.dll, not GLib.dll. And the names are indeed exported as GrfLoad etc.

It is very well possible that you have a glib.dll on your system too, but that won't contain the functions you are looking for.

---

Also note that most people don't like to download a zip from an unknown source. They can't know what is really in it.

Answer 2

It's solved! I just change the declaration from:

function GrfLoad(const fname: PChar; Modo: Boolean): Pointer; cdecl; external 'GLib.dll';

to:

function GrfLoad(const fname: PChar; Modo: Byte): Pointer; cdecl; external 'GLib.dll';

and the call from:

PVar:= GrfLoad(PChar('test.grf'),false);

to:

PVar:= GrfLoad(PChar('test.grf'),1);

And that's all. thanks to Mbo, Victoria and Rudy Velthuis for the help.