Re: offset of structure fields

[Eljay Love-Jensen <eljay at adobe dot com>]

Hi Massimiliano,

Try this...

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//I need to know the offset of the fields. For example f1[0].ff1 is placed 
at the offset 0, and f1[2].ff2, or f3?
//There is a way to obtain these offsets without have an istance of Param_t?

#include <stddef.h> /* stddef.h has offsetof macro. */

typedef unsigned short int u16_t;
typedef unsigned char u8_t;

typedef struct
{
    struct {
        u16_t ff1;
        u16_t ff2;
        u16_t ff3;
    } f1[3];
    u8_t f2;
    u8_t f3;
    u8_t f4;
    u16_t f5;
} Param_t;

int main()
{
    size_t dist;

    dist = offsetof(Param_t, f1[0].ff1);
    printf("f1[0].ff1 is at byte %lu\n", (unsigned long int)dist);

    dist = offsetof(Param_t, f1[2].ff2);
    printf("f1[2].ff2 is at byte %lu\n", (unsigned long int)dist);

    dist = offsetof(Param_t, f3);
    printf("f3        is at byte %lu\n", (unsigned long int)dist);
}

/* Output, using GCC 3.3.1 on Cygwin / WinNT
f1[0].ff1 is at byte 0
f1[2].ff2 is at byte 14
f3        is at byte 19
*/
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HTH,
--Eljay