Re: access violation

From: Ram Kumar (efextra_at_newsgroups.nospam)
Date: 08/02/04 

Date: Mon, 2 Aug 2004 11:35:32 +0530

Hi Carolyn,

I didn't find any access violation on running your code in VC 6.0 compiler.
code is given below -

#include "stdafx.h"

typedef struct tagTIMESTAMP_STRUCT
{
    short year;
    unsigned short month;
    unsigned short day;
    unsigned short hour;
    unsigned short minute;
    unsigned short second;
    unsigned int fraction;
} TIMESTAMP_STRUCT;

typedef struct
{
    int nCustomINDSeqNum;
    TIMESTAMP_STRUCT nCustomLastUpdateTime;
    char szField1[257];
    //...
    char szField255[257];
    unsigned int nNODE_ID;
    unsigned int nCUSTOM_APPLICATION_ID;
} ASPT_EDS_IND_CUSTOM;

//#define DS_C_TYPE(s,m) SetCType(((s *)&DS_SPACE::uDsTypes)->m)

inline short SetCType(unsigned int nValue)
{
 return 0;
}

typedef union
{
 unsigned __int64 u64;
 __int64 n64;
 unsigned int u32;
 int n32;
 unsigned short u16;
 short n16;
 unsigned char u8;
 char c8;
 TIMESTAMP_STRUCT ts;
 double d;
} DS_TYPESu;

namespace DS_SPACE
{
 static DS_TYPESu uDsTypes;
};

int main(int argc, char* argv[])
{
 printf("Hello World!\n");

 //short foo = DS_C_TYPE(ASPT_EDS_IND_CUSTOM, nNODE_ID); // access violation

 //Alternative is:
 short Raj_short = SetCType(((ASPT_EDS_IND_CUSTOM
*)&DS_SPACE::uDsTypes)->nNODE_ID);

 return 0;
}

Best Regards,
Ram Kumar

-------------------------------------------
"Carolyn Sano" <CarolynSano@discussions.microsoft.com> wrote in message
news:A57C3918-6B34-4506-997C-8412FB96128B@microsoft.com...
> Hi,
>
> I have hit an access violation in my code. I know exactly where it's
happening and what code is causing this. But I'd like someone to explain to
me why this doesn't work. If the following is too long and confusing, I can
cut and paste the code in an email (it's a pretty small test program that I
wrote). It's built in VS C++ 6.0 on Win 2K. Thanks.
>
> I have this large structure (~65568 bytes) that I wrote.
>
> My structure is defined as:
> typedef struct
> {
> int nCustomINDSeqNum;
> TIMESTAMP_STRUCT nCustomLastUpdateTime;
> char szField1[257];
> ...
> char szField255[257];
> unsigned int nNODE_ID;
> unsigned int nCUSTOM_APPLICATION_ID;
> } ASPT_EDS_IND_CUSTOM;
>
> My colleague's code is this macro:
> #define DS_C_TYPE(s,m) SetCType(((s *)&DS_SPACE::uDsTypes)->m)
>
> I call the macro like this:
> short foo = DS_C_TYPE(ASPT_EDS_IND_CUSTOM, nNODE_ID); // access violation
>
> The expansion of the macro is this: SetCType(((ASPT_EDS_IND_CUSTOM
*)&DS_SPACE::uDsTypes)->nNODE_ID)
>
> The method is this:
> inline short SetCType(unsigned int nValue)
> {
> return 0;
> }
>
> other stuff:
> typedef struct tagTIMESTAMP_STRUCT
> {
> short year;
> unsigned short month;
> unsigned short day;
> unsigned short hour;
> unsigned short minute;
> unsigned short second;
> unsigned int fraction;
> } TIMESTAMP_STRUCT;
>
> typedef union
> {
> unsigned __int64 u64;
> __int64 n64;
> unsigned int u32;
> int n32;
> unsigned short u16;
> short n16;
> unsigned char u8;
> char c8;
> TIMESTAMP_STRUCT ts;
> double d;
> } DS_TYPESu;
>
> namespace DS_SPACE { static DS_TYPESu uDsTypes; };
>
>

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