Struct on on x86_64 mac os x

Gabriel Genellina gagsl-py2 at
Wed Oct 21 05:23:19 CEST 2009

En Tue, 20 Oct 2009 18:51:21 -0300, Tommy Grav <tgrav at>  

> I have created a binary file that saves this struct from some C code:
>    struct recOneData {
>           char label[3][84];
>           char constName[400][6];
>         double timeData[3];
>       long int numConst;
>         double AU;
>         double EMRAT;
>       long int coeffPtr[12][3];
>       long int DENUM;
>       long int libratPtr[3];
>       };
> I try to read this file with python (ActiveState 2.6.3 on x86_64 Mac OS  
> X 10.6.1) using the
> code below the hdrData and constNData are fine, while from the timeData  
> onwards there
> are obvious problems. The code below works fine for a 32bit binary read  
> with i386 python
> 2.5.2. Does anyone know what the proper format of a C double and long  
> int is for a x86_64
> binary?

I'd start comparing at least both struct sizes to see if they match. Then,  
at the C side determine offset and size of each member using macros like  

#define COUNT_OF(_array) (sizeof(_array)/sizeof(*(_array)))
#define	OFFSET_OF(_structure, _member) ((size_t)&(((_structure  
#define SIZE_OF(_structure, _member) (sizeof((((_structure *)0)->_member)))

and then add padding bytes ('x') to the struct definition in Python to  
match those offsets (and probably use '=' for standard sizes).

Gabriel Genellina

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