README

H2Pas Converter

A Lazarus GUI tool that converts C header files (.h) into ready-to-use Pascal (FPC) or Python (ctypes) binding units — in one click.

Table of Contents

• What It Does
• Features
• Supported C Constructs
• Prerequisites
• Build from Source
• First Run
• Usage
• Example
• Project Structure
• Known Limitations
• Troubleshooting
• Documentation
• Contributing
• License
• About

What It Does

Instead of manually translating each typedef struct, typedef enum, #define, and function prototype from C to Pascal or Python, H2Pas Converter does it automatically:

• Pascal mode → generates a complete .pas unit with external declarations and cdecl calling convention
• Python mode → generates a .py module with ctypes CDLL, Structure subclasses, and argtypes/restype declarations

Features

✅ Automatic type mapping — 26 C types mapped to Pascal / ctypes equivalents
✅ Preprocessor — #define integer, float, and string constants converted
✅ Structs — typedef struct → Pascal record with {$PACKRECORDS C} / Python Structure
✅ Enums — typedef enum → Pascal integer type + constants / Python integer constants
✅ Opaque handles — typedef struct Foo_t* Foo → Pointer / c_void_p
✅ Functions — full external … name … / argtypes + restype output
✅ Pointer params — Circle* → PCircle (Pascal) / POINTER(Circle) (Python)
✅ const char* → PAnsiChar / c_char_p
✅ void return → procedure (Pascal) / restype = None (Python)
✅ Dual output — switch language with a radio button, no restart needed
✅ Save dialog — pre-fills filename and extension from the Unit field
✅ Conversion log — detailed journal of every element processed

Supported C Constructs

Prerequisites

Build from Source

1. Clone or download this repository:
   bashCopy

   git clone https://github.com/axel18bsm/BindingC_Dll_Pascal_Python.git
   cd BindingC_Dll_Pascal_Python

2. Open the project in Lazarus:
   • Open H2PasConverter\H2PasConverter.lpi in Lazarus IDE
3. Build & Run:
   • Press F9 or go to Run → Build & Run
4. First Build Notes:
   • If Lazarus reports a missing .res file:
     • Either: uncomment {$R *.res} in H2PasConverter.lpr after Lazarus generates it
     • Or: leave it commented — the application runs without it

First Run

1. The application window will open with three main panels:
   • Left panel: C header file input (browse or paste code)
   • Center panel: Settings (DLL name, Unit name, target language)
   • Right panel: Generated output code
   • Bottom panel: Conversion log

Usage

1. Load a C header file:
   • Click […] to browse for a .h file, or paste C code directly into the Source panel
2. Configure binding settings:
   • Verify the DLL name (e.g., raylib.dll)
   • Verify the Unit name (auto-filled from filename)
3. Select target language:
   • Choose Pascal (FPC) or Python (ctypes)
4. Generate bindings:
   • Click CONVERT
5. Review output:
   • Check the result in the right panel
   • Review the log at the bottom for any warnings or errors
6. Save the file:
   • Click Save .pas… (for Pascal) or Save .py… (for Python) to write to disk

Example

Input (mylib.h)

#define MYLIB_VERSION 200

typedef struct {
    int32_t x;
    int32_t y;
    float radius;
} Circle;

typedef enum {
    ERR_OK = 0,
    ERR_FAIL = 1
} ErrorCode;

typedef struct MyHandle_t* MyHandle;

int32_t __cdecl mylib_add(int32_t a, int32_t b);
MyHandle __cdecl mylib_open(const char *filename);
ErrorCode __cdecl mylib_process(MyHandle h, Circle c);
void __cdecl mylib_close(MyHandle h);

Pascal Output (uMylibBinding.pas)

unit uMylibBinding;

{$mode objfpc}{$H+}
{$PACKRECORDS C}

interface

uses
  SysUtils;

const
  MYLIB_VERSION = 200;

type
  Circle = record
    x: LongInt;
    y: LongInt;
    radius: Single;
  end;
  PCircle = ^Circle;

  ErrorCode = LongInt;
  MyHandle = Pointer;

const
  ERR_OK = 0;
  ERR_FAIL = 1;

function mylib_add(a: LongInt; b: LongInt): LongInt; cdecl;
  external 'mylib.dll' name 'mylib_add';

function mylib_open(filename: PAnsiChar): Pointer; cdecl;
  external 'mylib.dll' name 'mylib_open';

function mylib_process(h: Pointer; c: Circle): LongInt; cdecl;
  external 'mylib.dll' name 'mylib_process';

procedure mylib_close(h: Pointer); cdecl;
  external 'mylib.dll' name 'mylib_close';

implementation

end.

Python Output (mylib.py)

from ctypes import c_int32, c_float, c_char_p, c_void_p, POINTER, Structure, CDLL

lib = CDLL("mylib.dll")

MYLIB_VERSION = 200

class Circle(Structure):
    _fields_ = [("x", c_int32), ("y", c_int32), ("radius", c_float)]

ERR_OK = 0
ERR_FAIL = 1

MyHandle = c_void_p

lib.mylib_add.argtypes = [c_int32, c_int32]
lib.mylib_add.restype = c_int32

lib.mylib_open.argtypes = [c_char_p]
lib.mylib_open.restype = c_void_p

lib.mylib_process.argtypes = [c_void_p, Circle]
lib.mylib_process.restype = c_int32

lib.mylib_close.argtypes = [c_void_p]
lib.mylib_close.restype = None

Project Structure

H2PasConverter/
????????? H2PasConverter.lpi           # Lazarus project file
????????? H2PasConverter.lpr           # Application entry point
????????? uMainForm.pas                # GUI form ??? orchestration
????????? uMainForm.lfm                # GUI form design
????????? uCHeaderParser.pas           # C header parsing logic
????????? uTypeMapper.pas              # C ??? Pascal/Python type mapping
????????? uPascalGenerator.pas         # Pascal code generation
????????? uPythonGenerator.pas         # Python code generation
????????? README.md                    # This file

Known Limitations

⚠️ cdecl only — stdcall (Win32 API) functions are not auto-detected; add the keyword manually after generation
⚠️ Simple macros only — function-like macros (#define MAX(a,b) …) are ignored
⚠️ No C++ templates — pure C headers only (no C++ templates or namespaces)
⚠️ No bitfields — bitfield structs are not supported
⚠️ No GCC extensions — __attribute__ and other compiler-specific extensions not supported

Troubleshooting

Issue: "Cannot find Lazarus project file"

Solution: Ensure you extracted all files correctly and the .lpi file exists in the H2PasConverter directory.

Issue: "Missing .res file on first build"

Solution:

• Let Lazarus auto-generate the .res file
• Or uncomment {$R *.res} in H2PasConverter.lpr
• The application works fine without it

Issue: "DLL not found at runtime"

Solution:

• Ensure the DLL file path is correct and the DLL exists
• Copy the DLL to the same directory as your generated binding unit
• Or provide the full path in the binding unit's external declaration

Issue: "Type mapping is incorrect"

Solution:

• Check the conversion log in the bottom panel for warnings
• Verify the C header syntax is correct
• Report any issues on GitHub with the problematic C code

Issue: "Generated code won't compile in Pascal"

Solution:

• Check that Free Pascal 3.2.x is installed and in your PATH
• Verify all referenced units (like SysUtils) exist
• For linking issues, ensure {$PACKRECORDS C} is present

Issue: "Python module import fails"

Solution:

• Ensure ctypes is available (included in Python stdlib)
• Check that the DLL path in CDLL("…") is correct
• Verify the DLL architecture matches your Python installation (32-bit or 64-bit)

Documentation

Contributing

We welcome contributions! To contribute:

1. Fork the repository
2. Create a feature branch: git checkout -b feature/my-improvement
3. Make your changes and test thoroughly
4. Commit with clear messages: git commit -m "Add support for …"
5. Push to your fork: git push origin feature/my-improvement
6. Open a Pull Request with a clear description

Reporting Bugs

If you find a bug:

1. Check if it's already reported in Issues
2. Create a new issue with:
   • Your C header file (or example)
   • Expected vs. actual output
   • Your Lazarus/FPC versions
   • Steps to reproduce

License

MIT — free to use, modify, and distribute.

About

Built as a learning tool for the tutorial series "Learning to Bind a C DLL in Pascal".

Target stack: Free Pascal 3.2 · Lazarus 4.x · Windows 64-bit · cdecl calling convention