C / C++ / MFC

How to check iterator for NULL

2-Apr-12 6:43

Yourwelcome, glad it worked out. Good luck with the rest. Smile | :)

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> If it doesn't matter, it's antimatter.<

KASR12-Apr-12 2:24

2-Apr-12 2:24

XML

vector<int> vect;
vector<int>::iterator pBegin;

I want to check the iterator for NULL.
In VC6 we can compare if (pBegin == NULL) and it works. But in VC10 we cannot compare iterator to NULL.

How to achieve that in VC10?

Maximilien2-Apr-12 2:46

Maximilien

2-Apr-12 2:46

You should check against begin or end (usually past the end).

if you have

KASR1 wrote:
vector<int>::iterator pBegin;

Than it should be treated as an uninitialized variable, so it it give out bad results if used as-is.

As far as I know, the STL implementation in VC6 is crap and not standard.

Watched code never compiles.

KASR12-Apr-12 2:53

2-Apr-12 2:53

Ok. Lets assume its not initialized.
Can we consider checking
if (pBegin != vect.end()) in place of if( pBegin != NULL)

Maximilien2-Apr-12 3:00

Maximilien

2-Apr-12 3:00

You need to assign the iterator to something valid before using it.

C++

std::vector<int> v;
// fill the vector.

std::vector<int>::iterator pBegin = v.begin();

while ( pBegin != v.end() )
{
  // do something.
  ++it;
}

C++

if ( pBegin != v.end() )
{
  // ite
}

Watched code never compiles.

KASR12-Apr-12 3:24

2-Apr-12 3:24

Thanks for your input.

KASR12-Apr-12 4:28

2-Apr-12 4:28

XML

std::vector<int>::iterator pIter = v.end();

  //do Some operation on pIter

if ( pIter != v.end() )
{
 // do something

}

Is the above logic make sense?

Mapping logical drive to its physical drive

Stephen Hewitt3-Apr-12 7:34

Stephen Hewitt

3-Apr-12 7:34

Checking it against NULL is wrong. It's an implementation detail that it works in vc6 (because raw pointers are used, amongst other implementation specific details). Iterators are not required be pointers, in fact vectors are one of the few containers where they can do the job and as you've discovered even then they are not the only option.

Steve

VCProgrammer1-Apr-12 19:56

VCProgrammer

1-Apr-12 19:56

Hi all,

I want to map logical drive to its physical drive value i.e. if i give c: it should tell its hard disk number and partition number. For example if i give C: it should give \Device\HardDiskVolume1. For doing so i have used QueryDosDevice but it is not giving me correct answer. Here is my code

CString text;
GetDlgItemText(IDC_EDIT1,text);

TCHAR szBuffer[MAX_PATH];
bool bIsFloppy = false;
  
if (QueryDosDevice(text, szBuffer, MAX_PATH) > 0)
{
      CString buffer = szBuffer;
      AfxMessageBox(buffer);
}

But my code is giving incorrect result \Device\HardDiskVolume11

Can anybody please tell me what i am doing wrong?

Re: Mapping logical drive to its physical drive

Richard MacCutchan1-Apr-12 22:44

Richard MacCutchan

1-Apr-12 22:44

Your code is not incorrect; volume names are assigned internally by Windows and do not necessarily follow the order that you expect. There is lots of information in MSDN here[^] that helps to explain it.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

How to change the variable type on the fly?

Falconapollo1-Apr-12 7:17

Falconapollo

1-Apr-12 7:17

there are a struct:

struct _Tag
{
Type a;
Type b;
};

I just want to set the the type of a and b at runtime(i.e. set a to int and later set a to string within the same struct _Tag), don't tell me to use templates. For templates don't meet my requirements.

Another question:
There is a C++ statement:
AfxMessageBox(_T("Hello, world!"));
what I want to do is put the statement above into a
CString variable str. That is:

C++

CString str = _T("AfxMessageBox(_T(\"Hello, world!\"));");

I want to execute the statement stored in str later, so that the statement just like the ACTUAL MFC EXECUTABLE STATEMENT I typed.

I wonder whether C++ support such operations.

Any help will be appreciated!

Software_Developer1-Apr-12 8:49

Software_Developer

1-Apr-12 8:49

Have a look at [ this Variant class] and [MSDN]

Falconapollo1-Apr-12 15:28

Falconapollo

1-Apr-12 15:28

Thanks for reply!
You solved my first question.

But how about the second question?

CPallini1-Apr-12 21:37

CPallini

1-Apr-12 21:37

Falconapollo wrote:
I wonder whether C++ support such operations.

Nope, there is NO support for such operations. You have to build yourself a parser or embed a script engine in your application (for instance you may host, via <code>COM, VBScipt or JScript: have a look ath the following, bit dated, Codeproject article "Adding VBScript and JScript support in your C++ applications"[^]. Another nice option is Lua[^]).

Veni, vidi, vici.

Erudite_Eric1-Apr-12 22:05

Erudite_Eric

1-Apr-12 22:05

1) Use a union.

2) You cant compile code at run time. What you can do is use function pointers so you can select the behaviour you want at run time.

==============================

Nothing to say.

C, VB.net, MySql

kus_hal0331-Mar-12 22:56

kus_hal03

31-Mar-12 22:56

I have developed one GUI in vb.net but now I want to use C as backend code along with MySql as database.
Is it possible to create such a application.

I have been using C and MySql under Fedora and I have my GUI ready in vb.net. Can you tell me how can I communicate these thing together?

For ex. I have add button on front end, when I click add button, and instead of defining functionality in vb.net I want to send input to C function and then C function will execute and return output.

Re: C, VB.net, MySql

Code-o-mat31-Mar-12 23:13

31-Mar-12 23:13

Do you mean that you want the VB frontend running under windows to "do business" on a -most likely separate- machine running Fedora? If yes, i'd say, use a client-server aproach, run a server on the Fedora machine onto which your VB app connects and then sends commands (which are then executed by your C code) and receives results (created by your C code).

If you mean that you want the C code to also run on the windows machine, in my oppinion your best bet would be to create a DLL from your C code and then use it in a VB app with your frontend calling methods as needed.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> If it doesn't matter, it's antimatter.<

Re: C, VB.net, MySql

kus_hal0331-Mar-12 23:39

kus_hal03

31-Mar-12 23:39

Yes I want to use first approach means I will use client-server approach. But can you tell me how can I do this?

Re: C, VB.net, MySql

Code-o-mat31-Mar-12 23:54

About the screen shot is black or desktop.

31-Mar-12 23:54

Look into sockets under linux[^] and sockets under windows[^], i'd use TCP/IP or UDP depending on your needs. For VB related questions, target the VB forums here on CodeProject.
For the basic client-server aproach[^], Google is your friend.

> The problem with computers is that they do what you tell them to do and not what you want them to do. <
> If it doesn't matter, it's antimatter.<

wangningyu31-Mar-12 21:36

wangningyu

31-Mar-12 21:36

I use GDI or DirectX way to capture the screen shot.

In windows xp or 2003, the picture is normal, but in some win7 (32 or 64) system:

It is the desktop's image or whole black , when running a full screen game.

what's wrong ?

and how to fix it ? Smile | :)

What WM_??? does "ShowWindow" actually call and send

Stan the man31-Mar-12 5:40

Stan the man

31-Mar-12 5:40

Hi.

I was just wondering what exactly does ShowWindow(...) call (WM_ ???) ? I looked around but it does not seem that it calls WM_SHOWWINDOW. I want to send this message to another application with SW_HIDE etc...

Thanks in advance.

Stan the man

Re: What WM_??? does "ShowWindow" actually call and send

Richard MacCutchan31-Mar-12 6:10

Richard MacCutchan

31-Mar-12 6:10

I think you will find this page[^] and this one[^] give the details.

Unrequited desire is character building. OriginalGriff
I'm sitting here giving you a standing ovation - Len Goodman

Re: What WM_??? does "ShowWindow" actually call and send

Code-o-mat31-Mar-12 11:36