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C to Delphi: typedef struct ...

Posted on 2007-11-22
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Last Modified: 2010-05-18
I'm trying to convert some of the headers from GSL package written in C, into Delphi.

There are several fields in some structures which I can't interpret, for example: gsl_rng_type.

-----------------------------------------
typedef struct
  {
    const char *name;
    unsigned long int max;
    unsigned long int min;
    size_t size;
    void (*set) (void *state, unsigned long int seed);    // <- ???????
    unsigned long int (*get) (void *state);     // <- ???????
    double (*get_double) (void *state);    // <- ???????
  }
gsl_rng_type;
-----------------------------------------

I got as far as....
-----------------------------------------
  gsl_rng_type = packed record
    name: PChar;
    max: LongInt;
    min: LongInt;
    size: Cardinal;
-----------------------------------------
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Question by:den4b
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8 Comments
 
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Accepted Solution

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DeepuAbrahamK earned 300 total points
ID: 20333843
These are function pointers or in other words call back functions.Check what is the replacement for function pointers

void (*set) (void *state, unsigned long int seed);
unsigned long int (*get) (void *state);
double (*get_double) (void *state);
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Author Comment

by:den4b
ID: 20333853
I thought that they might be method pointers, but I'm not sure how to correctly translate them.... That is exactly my question.
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Author Comment

by:den4b
ID: 20333874
Would that be correct translation?
  _gsl_rng_type = packed record
    name: PChar;
    max: LongInt;
    min: LongInt;
    size: Cardinal;
    set_: procedure(state: Pointer; seed: LongInt);
    get_: function(state: Pointer): LongInt;
    get_double: function(state: Pointer): Double;
  end;

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Expert Comment

by:DeepuAbrahamK
ID: 20334105
Not sure about call backs in Delphi, but have a look
http://delphi.about.com/od/windowsshellapi/a/callback_delphi.htm
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Assisted Solution

by:MerijnB
MerijnB earned 200 total points
ID: 20334177
my guess you'll have to make a type for the functions:
type TProcSet = procedure(state: Pointer; seed: LongInt);
     PProcSet = ^TProcSet
 
     _gsl_rng_type = packed record
       name: PChar;
       max: LongInt;
       min: LongInt;
       size: Cardinal;
       set_: PProcSet;
       ...
     end;

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Author Comment

by:den4b
ID: 20334557
Can't test it yet, because I have to convert a lost more headers first, but it sound good already!

The only uncertain thing left is "set_: TProcSet" or "set_: PProcSet". I thought that "TProcSet" would already be a function pointer in Delphi, in which case I could use just "set_: procedure(state: Pointer; seed: LongInt)".

Anyway, I can check that out later...
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Expert Comment

by:MerijnB
ID: 20334568
I'm quite sure you'll need PProcSet, TProcSet is not a pointer itself.
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Author Comment

by:den4b
ID: 20334582
Ohh, the only thing which I forgot to mention is to use "cdecl" calling convention for the functions written in C. For example: procedure(state: Pointer; seed: LongInt); cdecl;
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