memory_allocation

memory_allocation

[simon.guinot]

hello,

i have a problem with a structure memory allocation...
 
struct dns_answer {
         unsigned short type;
         unsigned short class;
         unsigned int ttl;
         unsigned short rdlength;
         unsigned int addr_answer;
         } dns_answ;

all this element are not adjacent in memory... i have two
"free bytes" between rdlenght and addr_answer...
since here, i have alway made my headers like this... and no
problem...
an idea to force this structure elements to be adjacent in
memory ?
 
thank by advance for help

simon

ps : sorry for my poor english...


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Re: memory_allocation

[Henry Margies]

Hi

You could use -fpack-struct, if you are using gcc. But maybe there is
a finer solution.


Henry

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Re: memory_allocation

[Jan-Benedict Glaw]

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On Fri, 2004-08-13 14:27:51 +0200, simon.guinot <simon.guinot@laposte.net>
wrote in message <I2DXAF$7B97927BCA10A589B58FC0F34E16A58F@laposte.net>:
> hello,
> 
> i have a problem with a structure memory allocation...
>  
> struct dns_answer {
>          unsigned short type;
>          unsigned short class;
>          unsigned int ttl;
>          unsigned short rdlength;
>          unsigned int addr_answer;
>          } dns_answ;
> 
> all this element are not adjacent in memory... i have two
> "free bytes" between rdlenght and addr_answer...
> since here, i have alway made my headers like this... and no
> problem...

You can add  "__attribute__ ((packed))" to the declaration of that
struct to force GCC to pack it. However, keep in mind that the gap does
serve a purpose! Accessing those parts at unaligned offsets may cause
quite some speed penalty on some CPUs. However, if it's a binary
structure (as it looks like), that's okay. (NB: Is your coding
endianess-save in that case?)

MfG, JBG

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