Re: struct with variable length member

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From: Frank Hickman (fhickman_nosp_at_m_noblesoft.com)
Date: 03/20/04 

Date: Fri, 19 Mar 2004 22:31:55 -0500

I think you want a union, not a struct, maybe...it depends on what it is
your trying to do?

typedef union
{
    struct
    {
        WORD a1;
        WORD a2;
    };
    DWORD a3;
}AAA;

typedef union
{
    WORD b1;
    AAA b2[1];
}BBB;

BYTE buffer[]= {
    0x11, 0x22, 0x33,0x44,0x55,0x66,0x77,0x88,0x99,0xaa,0xbb,0xcc,0xdd
};
BBB* bbb= (BBB*)buffer; //cast to a union

int main( int argc, char* argv[] )
{
    printf( "bbb->b1 = %x bbb->b2[0].a1 = %x bbb->b2[0].a2 = %x\n",
        bbb->b1, bbb->b2[0].a1, bbb->b2[0].a2 );
    printf( "bbb->b2[0].a3 = %x\n", bbb->b2[0].a3 );

    if ( !getch() )
    {
        getch();
    }
    return 0;
}

produces...

bbb->b1 = 2211 bbb->b2[0].a1 = 2211 bbb->b2[0].a2 = 4433
bbb->b2[0].a3 = 44332211

HTH 

-- 
============
Frank Hickman
NobleSoft, Inc.
============
Replace the _nosp@m_ with @ to reply.
"lavut" <anonymous@discussions.microsoft.com> wrote in message
news:28DE3E3A-D30C-4798-973D-CBAF5E76AEC6@microsoft.com...
> Consider this piece of code.
> Can somebody tell me why the output below gives the wrong result when I
defined
> struct AAA with a3 as a DWORD?
>
> #include <windows.h>
> #include <stdio.h>
>
> BYTE buffer[]={0x11, 0x22,
0x33,0x44,0x55,0x66,0x77,0x88,0x99,0xaa,0xbb,0xcc,0xdd};
> typedef struct {
>  WORD a1;
>  WORD a2;
>  DWORD a3; //as a WORD output below ok, as a DWORD 4433 is not read
>
> }AAA;
>
> typedef struct {
>  WORD b1;
>  AAA b2[1];
> } BBB;
> BBB*bbb = (BBB*)buffer; //cast to a struct
>
> void main() {
> //with a3 as a WORD : 2211 4433 6655
> //with a3 as a DWORD: 2211 6655 8877 <----this is wrong, why?
> printf("%x %x %x", bbb->b1, bbb->b2[0].a1, bbb->b2[0].a2);
>
> }
>

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