Re: access dynamically allocated structure - C / C++ / MFC Discussion Boards

Re: access dynamically allocated structure

Eugen Podsypalnikov31-Mar-10 2:29

Eugen Podsypalnikov

31-Mar-10 2:29

Try this access in your loops Smile | :)

{
  CheckSumPair* psTempPair = (CheckSumPair*) ((BYTE*)CSPair + sizeof(CheckSumPair) * x);
  // psTempPair->Member1
  // psTempPair->Member2
}

virtual void BeHappy() = 0;

Re: access dynamically allocated structure

Richard MacCutchan31-Mar-10 2:35

Richard MacCutchan

31-Mar-10 2:35

Eugen Podsypalnikov wrote:
CheckSumPair* psTempPair = (CheckSumPair*) ((BYTE*)CSPair + sizeof(CheckSumPair) * x);

All this casting is unnecessary and prone to error, the compiler handles pointer arithmetic automatically.

txtspeak is the realm of 9 year old children, not developers. Christian Graus

Re: access dynamically allocated structure

Eugen Podsypalnikov31-Mar-10 2:37

Eugen Podsypalnikov

31-Mar-10 2:37

In this case - it is necessary,
since sizeof(CheckSumPair*) != sizeof(CheckSumPair) ! Smile | :)

virtual void BeHappy() = 0;

Re: access dynamically allocated structure

Richard MacCutchan31-Mar-10 3:03

Richard MacCutchan

31-Mar-10 3:03

Pointers to structures can be incremented by simple expressions thus:

CSPair++;

that is all that is needed to point to the next entry in the array.

txtspeak is the realm of 9 year old children, not developers. Christian Graus

Re: access dynamically allocated structure

Eugen Podsypalnikov31-Mar-10 3:09

Eugen Podsypalnikov

31-Mar-10 3:09

Yes, they can !!! Big Grin | :-D

You are right, Richard !
(probably I was intricated by malloc... Big Grin | :-D

)
Thank you very much ! Thumbs Up | :thumbsup:

virtual void BeHappy() = 0;

Re: access dynamically allocated structure

rupeshkp72831-Mar-10 2:35

rupeshkp728

31-Mar-10 2:35

thanks eugen for the reply
that was a typing mistake
issue is resolved by using
CheckSumpair[x].memberN;
.
.
.
since i am using [] operator to access pointer no need of using ->

Re: access dynamically allocated structure

Richard MacCutchan31-Mar-10 2:32

Richard MacCutchan

31-Mar-10 2:32

The address CSPair[x] is a structure reference not a pointer, hence use the '.' member access operator.

txtspeak is the realm of 9 year old children, not developers. Christian Graus

Re: access dynamically allocated structure

CPallini31-Mar-10 2:36

CPallini

31-Mar-10 2:36

Your code is really ugly.

rupeshkp728 wrote:
#define UINT32 unsigned int
#define INT32 int
#define UCHAR unsigned char

Why do you use #define instead of typedef?

rupeshkp728 wrote:
typedef struct CheckSumPair
{
UINT32 weakcs; // The weak, rolling Adler32 checksum.
UCHAR StrongCS[10];
};

Typedef what?

rupeshkp728 wrote:
CheckSumPair* CSPair = (CheckSumPair*)malloc(sizeof(CheckSumPair)*10);

Why are you using malloc? Do you really need to use C memory allocation functions?

rupeshkp728 wrote:
strncpy((char*)CSPair->StrongCSString,(char*)"CEDVCD",10*2+1);

struct CheckSumPair has no StrongCSString member.

rupeshkp728 wrote:
printf("%d %s %s\n\n",CSPair[x]->.weakcs,CSPair[x]->StrongCS,CSPair[x]->StrongCSString);

This is the ugliest part. What are you trying to do?

Smile | :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: access dynamically allocated structure

KingsGambit31-Mar-10 2:36

KingsGambit

31-Mar-10 2:36

I think you have to print the values as follows:

for(int x = 0; x < 10; x++)
   printf("%d %s %s\n\n",CSPair[x].weakcs, CSPair[x].StrongCS, CSPair[x].StrongCSString);

for(int x = 0; x < 10; x++)
{
   printf("%d %s %s\n\n",CSPair->weakcs,CSPair->StrongCS,CSPair->StrongCSString);

   CSPair++;
}

Re: access dynamically allocated structure

Member 392263931-Mar-10 2:52

Member 3922639

31-Mar-10 2:52

Don't you have a warning "warning C4091: 'typedef ' : ignored on left of 'CheckSumPair' when no variable is declared"?
Don't you have an error "error C2039: 'StrongCSString' : is not a member of 'CheckSumPair'"?
Type of CSPair[x] is CheckSumPair not CheckSumPair*, so you can't use "->", use "." instead.
Instruction "CSPair[x]->.weakcs" contains "->" and ".".
Why malloc? use the new operator instead:

CheckSumPair* CSPair = new CheckSumPair[10];

or better, if possible:

CheckSumPair CSPair[10];

And finally, you have to explain what are you trying to do with the two strncpy, maybe your code has to be like:

#define UINT32 unsigned int
#define INT32 int
#define UCHAR unsigned char

typedef struct
{
	UINT32 weakcs; // The weak, rolling Adler32 checksum.
	UCHAR StrongCS[10 + 1]; // including the string terminator
	UCHAR StrongCSString[10 + 1]; // including the string terminator
} CheckSumPair;

int main()
{
	CheckSumPair CSPair[10];

	for(int x = 0; x < 10; x++)
	{
		CSPair[x].weakcs = (UINT32)x+1;
		strncpy((char*)CSPair[x].StrongCS, "XYZ", 10);
		strncpy((char*)CSPair[x].StrongCSString, "CEDVCD", 10);
	}


	for(int x = 0; x < 10; x++)
	{
		printf("%d %s %s\n\n", CSPair[x].weakcs, CSPair[x].StrongCS, CSPair[x].StrongCSString);
	}

	return 0;
}

error C2664

002comp30-Mar-10 22:18

002comp

30-Mar-10 22:18

Hello Friends
While compiling 32bit code on 64 bit compiler,I came across one error is

error C2664: 'SetTimer' : cannot convert parameter 4 from 'void (__cdecl *)(HWND,UINT,UINT,DWORD)' to 'TIMERPROC'

Do u have any Ideas to resolve this?
Regards
Yogesh

Re: error C2664

KingsGambit30-Mar-10 22:27

KingsGambit

30-Mar-10 22:27

Forgot to mention CALLBACK in TimerProc declaration?

Re: error C2664

002comp30-Mar-10 23:16

002comp

30-Mar-10 23:16

That I am using CALLBACK in Declaration.

But I got it to work after casting fourth parameter to TIMERPROC.
IS this the right way?

Thanks
Yogesh

Re: error C2664 [modified]

CPallini30-Mar-10 23:28

CPallini

30-Mar-10 23:28

Nope.

However, as Rejeesh suggested, even in Microsoft samples there is the 'cast-hack'.

Anyway, at least on my system, the following declaration:

void CALLBACK myTimerFun(HWND , UINT , UINT_PTR , DWORD );

compiles fine, without the need of casting.
Smile | :)

modified on Wednesday, March 31, 2010 5:47 AM

Re: error C2664

Eugen Podsypalnikov31-Mar-10 0:00

Eugen Podsypalnikov

31-Mar-10 0:00

Right

The third parameter may not be a UINT under x64,
it must be UINT_PTR Smile | :)

virtual void BeHappy() = 0;

Re: error C2664 [modified]

002comp31-Mar-10 1:54

002comp

31-Mar-10 1:54

I got it the way u defined and without casting.
thanks

Yogesh

modified on Wednesday, March 31, 2010 8:14 AM

Re: error C2664

KingsGambit30-Mar-10 23:34

KingsGambit

30-Mar-10 23:34

It is always better to avoid type casting if possible. But you can see the MSDN samples for SetTimer() uses type casting Smile | :)

http://msdn.microsoft.com/en-us/library/ms644901(v=VS.85).aspx#creating_timer[^]

Re: error C2664

002comp31-Mar-10 1:35

002comp

31-Mar-10 1:35

So Rajneesh without Type casting ,Is there any other way to solve my prob?
As In my case I am using CALLBACK in declaration.

Thanks
Yogesh

Re: error C2664

KingsGambit31-Mar-10 2:03

KingsGambit

31-Mar-10 2:03

As CPallini suggested change the function signature of Timer proc as follows:

VOID CALLBACK TimerProc(HWND hwnd,
UINT uMsg,
UINT_PTR idEvent,
DWORD dwTime
);

I hope, that would compile without casting.

Re: error C2664

002comp31-Mar-10 2:14

002comp

31-Mar-10 2:14

Yeah,that CPallini method works.
THanks

Re: error C2664

KingsGambit31-Mar-10 2:18

KingsGambit

31-Mar-10 2:18

In fact, if you look at the TIMERPROC definition in winuser.h it is as follows:

typedef VOID (CALLBACK* TIMERPROC)(HWND, UINT, UINT_PTR, DWORD);

Re: error C2664

002comp31-Mar-10 2:28

002comp

31-Mar-10 2:28

Fine, thanks buddy.

Re: error C2664

Emilio Garavaglia30-Mar-10 23:57

Emilio Garavaglia

30-Mar-10 23:57

CALLBACK should be present either in declaration (.h file) and definition (.cpp file).

Otherwise they are two different functions.

In your case the compiler knows about a CALLBACK prototype, by supply a __cdecl function to the linker (it wold have been __stdcall instead).

casting a __cdecl into a __stdcall is dangerous, since the stack is managed differently (you can overwrite some caller / callee local variables ... that could lead to very nasty bugs!

2 bugs found.
> recompile ...
65534 bugs found.
D'Oh! | :doh:

Re: error C2664

arun_pk30-Mar-10 23:26

arun_pk

30-Mar-10 23:26

try giving 4th param as 0

Can the OnSelchange event of the combo box be accessed in any other page

hansrajlal30-Mar-10 21:00

hansrajlal

30-Mar-10 21:00

Hello everyone, I wanted to know if the OnSelChange event of the combo box can be accessed outside of the dialog file, as i need to access and change the code in a different file within the same project.

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.