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AW: "sizeof" get unwanted result



> -----Ursprüngliche Nachricht-----
> Von: gcc-help-owner@gcc.gnu.org [mailto:gcc-help-owner@gcc.gnu.org]Im
> Auftrag von Xiaoshan Sun
> Gesendet: Dienstag, 19. April 2005 04:48
> An: gcc-help@gcc.gnu.org
> Betreff: "sizeof" get unwanted result
> 
> 
> hi,
>    i use "sizeof" to get the size of a struct ,defined as:
>    typedef struct _A {
>      long data1;
>      unsigned short data2;
>      long  data3;
>    }A;
>  i guess the sizeof(A) should be 10 .however when i compile 
> and print the
> value of "sizeof(A)" ,the reult is 12!!
>  so where's the extra 2 bytes? how can i get the gcc to calculate the
> desired size ??
> an aligned issue??
On a 32bit machine the compiler align each element on a 32bit even address. So between data2 and data3 there be 2 Byte filldata. On a 64bit machine the compiler align addresses to 64bit so he fill with 6 Bytes. 

To avoid use the packed attribute as proposed by Kevin.

regards
  Martin


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