C / C++ / MFC

Re: Caret not displayed in CEdit control with focus when dialog initially displayed

14-May-20 23:53

You should use the OnInitDialog method of CDialog Class | Microsoft Docs[^] to set the focus.

Member 1106593315-May-20 0:36

Member 11065933

15-May-20 0:36

Richard MacCutchan wrote:
You should use the OnInitDialog method of CDialog Class | Microsoft Docs[^] to set the focus.

I stated that the focus edit is being set from the OnInitialUpdate override of the CFormView derived class, I should have clarified that this has been called from the CDialog OnInitDialog method via a call to

SendMessageToDescendants(WM_INITIALUPDATE, 0, 0, TRUE, TRUE);

Also, the OnInitDialog method returns FALSE to indicate that I have set the focus to a control.
.

Re: Caret not displayed in CEdit control with focus when dialog initially displayed

Richard MacCutchan15-May-20 0:48

Possible to #if in case an enum exists?

15-May-20 0:48

Sorry, I cannot help further as I don't have MFC.

arnold_w11-May-20 22:21

arnold_w

11-May-20 22:21

Is it possible to somehow check during compile time if an enum exists, i.e. something like this:

typedef enum {
    MY_ENUM_VALUE = 0
} myEnum_e;

#define DOES_ENUM_EXIT(__ARG__)       ??? What goes here???

if (DOES_ENUM_EXIT(myEnum)) {     // Will evaluate to TRUE during compile time since myEnum_e exists
}

I know that I could achieve something similar easily be using

#define MY_ENUM_VALUE    (0)

instead, but then my code wouldn't be type safe.

CPallini11-May-20 22:48

CPallini

11-May-20 22:48

Nope (AFAIK), see Conditional inclusion - cppreference.com[^].

Richard MacCutchan11-May-20 23:29

11-May-20 23:29

No, because the #define statement is handled by the preprocessor, and the enum value is not known until it is fed into the compiler, which comes later.

Robust Services Core | Software Techniques for Lemmings | Articles

Greg Utas15-May-20 0:22

Greg Utas

15-May-20 0:22

Richard MacCutchan15-May-20 0:29

15-May-20 0:29

Reading sectors

_Flaviu8-May-20 5:46

8-May-20 5:46

I have written a little piece of code to read few (first 512) bytes from USB drive. here is the code:

C++

HANDLE hVolume = ::CreateFile(sVolume, GENERIC_READ,
    FILE_SHARE_READ | FILE_SHARE_WRITE,
    NULL, OPEN_EXISTING, FILE_FLAG_SEQUENTIAL_SCAN, NULL);
TRACE("Volume handle: %p\n", hVolume);
LONG lDistLow = 0;
PLONG plDistHigh = 0;
if (INVALID_SET_FILE_POINTER == SetFilePointer(hVolume, lDistLow, plDistHigh, FILE_BEGIN) &&
    NO_ERROR != GetLastError())
{
    TRACE("Error: %d\n", GetLastError());
    return FALSE;
}
else
{
    TRACE("%d\t%d\n", lDistLow, plDistHigh);
}

DWORD dwLen = 512;
DWORD dwNum = 0;
void* pBuffer = NULL;
ReadFile(hVolume, pBuffer, dwLen, &dwNum, NULL);
TRACE("%p\t%d\t%d\n", pBuffer, dwLen, dwNum);

but the result is:

C++

Volume handle: 00000438
0	0
00000000	512	0

this pBuffer NULL tell me that I am not able to read that sectors ... why ? The program is running as admin and sVolume is feed by _T("\\\\.\\F:"), first TRACE macro printed is a prove that is OK that part. SetFilePointer is used to position the reading part, and I intend to setup offset to the beginning, right ?

Victor Nijegorodov8-May-20 6:15

Victor Nijegorodov

8-May-20 6:15

What does ReadFile return? TRUE or FALSE?

_Flaviu9-May-20 19:55

9-May-20 19:55

The ReadFile function returned FALSE, which tell me that reading has failed.

Victor Nijegorodov9-May-20 20:49

Victor Nijegorodov

9-May-20 20:49

In this case you have to call GetLastError to obtain the exact reason of the failure!

_Flaviu9-May-20 21:21

9-May-20 21:21

I didn't feed correctly the buffer. After I setup correctly that parameter, ReadFile return TRUE.

Graham Breach8-May-20 6:22

Graham Breach

8-May-20 6:22

Your pBuffer value is NULL, so you are trying to read data into the memory address 0 - you have to allocate some space to read the data into and use that for your pBuffer value. For 512 bytes a stack-based array should do the trick.

Richard MacCutchan8-May-20 6:46

8-May-20 6:46

_Flaviu wrote:
pBuffer NULL tell me that I am not able to read that sectors

No, pBuffer = NULL; tells you that you have not allocated any space to pBuffer. And don't use void* unless you are trying to allocate nothing.

You can allocate space either of the following ways.

C++

unsigned char* pBuffer = new unsigned char[dwLen]; // allocate some space for the data to be read into
// or
unsigned char buffer[dwLen]; // allocate on the stack
ReadFile(hVolume, buffer, dwLen, &dwNum, NULL);

_Flaviu9-May-20 20:31

9-May-20 20:31

Is not accepted:

C++

unsigned char buffer[dwLen]; // error C2057: expected constant expression

Of course, putting 512 is ok, but I need to allocate that length of buffer through a variable.
I prefer this option, on stack, as far as I know, is faster than heap.

Richard MacCutchan9-May-20 21:32

9-May-20 21:32

You can fix that easily by doing it this way:

C++

#define SECTOR_SIZE 512
DWORD dwLen = SECTOR_SIZE;
DWORD dwNum = 0;
char buffer[SECTOR_SIZE];
ReadFile(hVolume, buffer, dwLen, &dwNum, NULL);

If you are using C++ then instead of #define you can use this:

C++

const int SECTOR_SIZE = 512

_Flaviu9-May-20 21:34

9-May-20 21:34

Good idea. I have tried in this way:

C++

CByteArray arrByte;
arrByte.SetSize(512);
BOOL bRet = ReadFile(hVolume, arrByte.GetData(), dwLen, &dwNum, NULL);

and seem to go well.

Richard MacCutchan9-May-20 22:13

9-May-20 22:13

If you are writing MFC code then you should be using CFile to handle all your I/O.

_Flaviu9-May-20 22:24

9-May-20 22:24

I'll try to use CFile Class | Microsoft Docs[^]

Can I replace SetFilePointer as well with something from MFC yard ?

modified 10-May-20 4:42am.