C function pointer translation into Delphi/Pascal?

Question

I am currently translating some C headers into Delphi. I am unable find a reference for converting a function pointer from C into Delphi.

typedef _JAlloc JAlloc;  
struct _JAlloc {  
    void *(*alloc) (JAlloc *allocator, size_t size);  
    void (*free) (JAlloc *allocator, void *p);  
    void *(*realloc) (JAlloc *allocator, void *p, size_t size);  
};

What will be the Delphi translation of this?
Where can I find good resources for manual conversion of C headers to Delphi (including pointer, preprocessor directives, etc.)?

Accidentally entered an answer as a comment (see below for my answer). — Tim Young - Elevate Software
– Tim Young - Elevate Software, Commented Jan 20, 2011 at 11:24

Arnaud Bouchez · Accepted Answer · 2011-01-20 10:33:19Z

9

Use this kind of code

type
  PJAlloc = ^TJAlloc;
  TJAllocAlloc = function(allocator: PJAlloc; size: integer): pointer; cdecl;
  TJAllocFree = procedure(allocator: PJAlloc; p: pointer); cdecl;
  TJAllocRealloc = function(allocator: PJAlloc; p: pointer; size: integer); cdecl;
  TJAlloc = record
    alloc: ^TJAllocAlloc;
    free: ^TJAllocFree;
    realloc: ^TJAllocRealloc;
  end;

And change cdecl to stdcall, depending of the calling convention of your C library.

An alternative declaration (more 'pascalish' perhaps) could be:

type
  TJAllocAlloc = function(var allocator: TJAlloc; size: integer): pointer; cdecl;
  TJAllocFree = procedure(var allocator: TJAlloc; p: pointer); cdecl;
  TJAllocRealloc = function(var allocator: TJAlloc; p: pointer; size: integer); cdecl;
  TJAlloc = record
    alloc: ^TJAllocAlloc;
    free: ^TJAllocFree;
    realloc: ^TJAllocRealloc;
  end;

answered Jan 20, 2011 at 10:33

Arnaud Bouchez

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4 Comments

Ramnish Over a year ago

Thanks Bouchez. Do you know where could i find more information about translating from C to delphi in internet? I am currently using Rudy's Blog.

Arnaud Bouchez Over a year ago

@Ramnish I don't have any resource at hand. I learned it with experiment. But take a look at some manual conversion of some C APIs (like OpenGL/GDI+/SQLite) and you'll find some tips. What is nice with Delphi is that you can compile the C code with C++ builder (including the free command line compiler), then link the resulting .obj to your Delphi unit. I've used some low-level asm tips like _ftol/_ftoul/_lldiv/_llshr and such in synopse.info/fossil/finfo?name=SQLite3/SQLite3.pas

Arnaud Bouchez Over a year ago

@Ramnish take a look at this site: rvelthuis.de/articles/articles-cobjs.html

Marco van de Voort Over a year ago

a procedural variable is already a pointer, so the ^ in the TJAlloc record for every field is wrong? Or am I mistaken?

Tim Young - Elevate Software · Accepted Answer · 2011-01-20 11:26:36Z

1

Dr. Bob's HeadConv utility is a good one to use for converting C declarations into Delphi, and is a good learning tool for comparing C source code to the equivalent Pascal source code.

You can find it here

answered Jan 20, 2011 at 11:26

Tim Young - Elevate Software

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1 Comment

Tim Young - Elevate Software Over a year ago

It worked for the ODBC 3.0 API headers, with a few tweaks to the resultant code. As for ancient - C hasn't changed, nor has the Pascal syntax for calling external DLLs and libraries, in the last 12-15 years.

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