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Dark Byte
Site Admin
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Joined: 09 May 2003
Posts: 25962
Location: The netherlands
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 Posted: Tue Aug 11, 2009 12:47 pm Post subject: structure length/internal alignment |
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Can someone tell me why the following structure returns size 11 ?
I can fix it by replacing the bit addressable elements with a byte and do the bitwise operations myself, but just wondering, shouldn't the #pragma pack(1) have fixed it, or is that the cause of the problem here ?
| Code: |
#pragma pack(1)
typedef struct _XXX
{
WORD a;
WORD b;
BYTE c;
unsigned d1: 3;
unsigned d2: 1;
unsigned d3: 1;
unsigned d4: 2;
unsigned d5: 1;
WORD e;
} XXX, *PXXX;
#pragma pack()
...
XXX bla;
if (sizeof(bla) != 8)
{
...
}
return ERROR;
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Polynomial
Grandmaster Cheater
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Joined: 17 Feb 2008
Posts: 524
Location: Inside the Intel CET shadow stack
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| Posted: Tue Aug 11, 2009 1:42 pm Post subject: |
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Have you tried specifying them as unsigned short? I know it's the same thing technically, but I've seen a few posts regarding this issue that seem to be similar to this. Maybe it's a compiler bug.
| Code: | #pragma pack(1)
typedef struct _XXX
{
WORD a;
WORD b;
BYTE c;
unsigned short d1: 3;
unsigned short d2: 1;
unsigned short d3: 1;
unsigned short d4: 2;
unsigned short d5: 1;
WORD e;
} XXX, *PXXX;
#pragma pack()
...
XXX bla;
if (sizeof(bla) != 8)
{
...
}
return ERROR; |
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BanMe
Master Cheater
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Joined: 29 Nov 2005
Posts: 375
Location: Farmington NH, USA
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| Posted: Tue Aug 11, 2009 3:08 pm Post subject: |
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| Code: |
#pragma pack(1)
typedef struct _XXX
{
WORD a;
WORD b;
BYTE c;
unsigned char d1: 3;
unsigned char d2: 1;
unsigned char d3: 1;
unsigned char d4: 2;
unsigned char d5: 1;
WORD e;
} XXX, *PXXX;
#pragma pack()
XXX bla = {0};
DWORD blah = sizeof(bla);
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C++ defaults to int for unspecified types..
this works as I think this is what you where trying to do..
regards BanMe
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Polynomial
Grandmaster Cheater
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Flyte
Peanuts!!!!
 Reputation: 6
Joined: 19 Apr 2006
Posts: 1887
Location: Canada
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| Posted: Wed Aug 12, 2009 1:28 pm Post subject: |
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| Code: | #include <stdio.h>
#include <stddef.h>
#pragma pack(1)
typedef struct _XXX
{
unsigned short a;
unsigned short b;
unsigned char c;
union {
unsigned char d1: 3;
unsigned char d2: 1;
unsigned char d3: 1;
unsigned char d4: 2;
unsigned char d5: 1;
} d;
unsigned short e;
} XXX, *PXXX;
int main()
{
printf("%d\n", sizeof(XXX));
printf("%d ", offsetof(XXX, a));
printf("%d ", offsetof(XXX, b));
printf("%d ", offsetof(XXX, c));
printf("%d ", offsetof(XXX, d));
printf("%d ", offsetof(XXX, e));
return 0;
} |
Since you are using microsoft specific defines, you could also use __declspec(align(1)) if you so desired.
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