C / C++ / MFC Discussion Boards

GDavy30-Mar-04 22:48

30-Mar-04 22:48

Hi guys,

A question:
I got a class A that has a overridden copy constructor and assignment operator.
I derive class B from A.

*If B does not have an overridden copy constructor or assignment operator will the assignments of objects of class B invoke the copy constr. or assign operator of class A for the A part of class B(if you know what I mean)?

eg:

class A
{
class A();
class A( const A& a);
A& operator=(const A& a);
...
};

class B: public A
{
...
};

int main()
{
B obj1, obj2;
...
obj2 = obj1; //is operator= of class A called?
B obj3 = obj2; // is copy construct of class A called?
}

Greetings,
Davy

Re: copy constructor / assignment operator

22491730-Mar-04 23:13

224917

30-Mar-04 23:13

no, you ll have to modify like this

B obj1;
A obj2;

obj2 = obj1; //operator= of class A is called
A obj3 = obj2; //copy construct of class A is called

but remember ur objects will have to be sliced..

greatest thing is to do wot others think you cant
suhredayan@omniquad.com>

messenger :suhredayan@hotmail.com

Re: copy constructor / assignment operator

Prakash Nadar31-Mar-04 5:04

Prakash Nadar

31-Mar-04 5:04

Suhredayan P wrote:
ur objects will have to be sliced..

woah whats that ? OMG | :OMG:

MSN Messenger.
prakashnadar@msn.com

Tip of the day of visual C++ IDE.
"We use it before you do! Visual C++ was developed using Visual C++"

Re: copy constructor / assignment operator

David Crow31-Mar-04 2:14

David Crow

31-Mar-04 2:14

Can you set a breakpoint on the line(s) in question to see what happens?

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

random number

shiva shankar30-Mar-04 22:21

shiva shankar

30-Mar-04 22:21

Can someone pls provide me with an algorithim that generates an random number ( 0 to 1000)and it cannot generate the same random number more than once.

Re: random number

SJolly30-Mar-04 23:11

SJolly

30-Mar-04 23:11

The output wouldn't be a random number as you are affecting the outcome, however to generate random numbers:

// seed the random number generator using the current time
srand((unsigned)time(NULL));

// gets a random number between 0 and 0x7fff
int iRandom = rand();

// scale this number down to a value between 0 and 1000.
iRandom /= (RAND_MAX / 1000);

Regards,
Simon

Re: random number

shiva shankar30-Mar-04 23:28

shiva shankar

30-Mar-04 23:28

thanks for your replay Mr.simon

but with // seed the random number generator using the current time
srand((unsigned)time(NULL));

the number will be repeated, but for me numbers shouldn't repeated in same sequence .

Re: random number

Antony M Kancidrowski30-Mar-04 23:49

Antony M Kancidrowski

30-Mar-04 23:49

You could hold all generated random numbers in a vector and check that the next number has not been used previously. If it has call the random again.

As long as you only want a few, i.e small percentage of the possible 1000 pseudo random numbers in your sequence, this will suffice.

Ant.

Re: random number

SJolly30-Mar-04 23:50

SJolly

30-Mar-04 23:50

The numbers will be repeated in the same sequence only if you start two copies of the application at the same time - the numbers are psuedorandom.

If that isn't good enough then you could seed the timer again each time you get a new random number - then differences such as the processor speed / load etc will mean that the sequence will definitely not be repeated.

Regards,
Simon

Re: random number

Tim Smith31-Mar-04 3:53

Tim Smith

31-Mar-04 3:53

Seeding the random number generator each time is a VERY BAD IDEA. For example, if you can generate 10,000 random numbers in a second, you will get the same random number each time since time only has a resolution of a second.

Also, many random number generators should be initialized with a large prime number. By not doing that, it can take a few interation before the random numbers start getting "good". Reseeding the random number generator constantly places it back in the initial condition of generating a small series of bad values.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Re: random number

SJolly31-Mar-04 4:53

SJolly

31-Mar-04 4:53

Yes, my bad - I forgot that the time bit was in seconds.

Re: random number

David Crow31-Mar-04 2:21

David Crow

31-Mar-04 2:21

The return value of time() is the number of seconds since January 1, 1970 00:00 (or December 31, 1969 19:00). In any case, as long as its not called two successive times in less than one second, the return value will always be different so srand() will always be seeded uniquely.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

Re: random number

Paul Ranson31-Mar-04 2:20

Paul Ranson

31-Mar-04 2:20

class IncInt<br />
{<br />
private :<br />
    int i_ ;<br />
public :<br />
    IncInt ( int i ) : i_ ( i ) {}<br />
<br />
    int operator () ()<br />
    {<br />
        return i_++ ;<br />
    }<br />
} ;<br />
<br />
void Random1000 ()<br />
{<br />
    std::vector<int> vi ;<br />
    vi.resize ( 1000 ) ;<br />
    std::generate ( vi.begin (), vi.end (), IncInt ( 0 )) ;<br />
    std::random_shuffle ( vi.begin (), vi.end ()) ;<br />
    // do something with randomised sequence...<br />
}

Gives you vector containing 0-999 in random order. You can use a custom 'random' function as an extra argument to 'random_shuffle' if you wish. I'll leave it up to you to decide how to wrap this up, should it suit your purpose.

Paul

Re: random number

Tim Smith31-Mar-04 3:57

Tim Smith

31-Mar-04 3:57

void Random1000 ()
{
  std::vector vi ;
  for (int i = 0; i < 1000; i++)
    vi .push_back (i);
  std::random_shuffle ( vi.begin (), vi.end ()) ;
// do something with randomised sequence...
}

If you don't want all that STL obfuscation in there. Why write 15 lines of code when 2 works just fine.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Re: random number

Paul Ranson31-Mar-04 4:20

Paul Ranson

31-Mar-04 4:20

I only had to write one line.... But it was necessary to cut and paste a bit to make it make sense here.

Anyway it's the ease of using the random_shuffle that's important. The OP didn't want a sequence of random numbers, AFAICT.

It could of course be written,

<br />
void Random1000()<br />
{<br />
int vi [ 1000 ] ;<br />
for ( int i = 0; i < 1000; ++i )<br />
vi [ i ] = i ;<br />
std::random_shuffle ( vi, vi + 1000 ) ;<br />
...<br />
}<br />

Paul

mpeg streamer

Florin Ochiana30-Mar-04 22:10

Florin Ochiana

30-Mar-04 22:10

Hi,

I want to build a module in my app that will alow me to stream the video from my webcam. Anybody knows any open source app or any article on this matter? I don't know how to start.

Thanks

-----
We are what we repeatedly do. Excellence, then, is not an act, but a habit.

DirectInput Gamepad axes name localization....

haust30-Mar-04 21:59

haust

30-Mar-04 21:59

hi,

the DIJOYSTATE2 struct is used to retreive the current state of a gamepad.
two members are standardized (lX, lY). when i say standardized i mean that you can localize a human readable equivalent ("left", "right", "up", "down" in english ; "gauche", "droite", "haut", "bas" in french ; etc).
for other members i didn't find a way to localize them since from a gamepad to another the same member can map a different axe....

is there a function in DirectInput that could help me on this case ??
any hint/suggestion is welcome.

thanks.

about socket

Member 98096830-Mar-04 21:32

Member 980968

30-Mar-04 21:32

i use "connect" and "send" to send a broadcast,then i use sniffer find i get the response , but i have no idea to use "receive" to get the info of response D'Oh! | :doh:

,can someone help me how to get the info of the response plz?

Re: about socket

Antony M Kancidrowski31-Mar-04 0:24

Antony M Kancidrowski

31-Mar-04 0:24

Here is an example that will wait upto 5 seconds for a reply

struct timeval	tv;
fd_set		set;
int		xfd;

// Timeout
tv.tv_sec = 5;
tv.tv_usec = 0;
		
FD_ZERO(&set);
FD_SET(Socket, &set);

if ((xfd = select(Socket + 1, &set, NULL, NULL, &tv)) == SOCKET_ERROR)
{
    // Error
}

// Wait upto timeout for data to arrive on the socket		
if (FD_ISSET(Socket, &set))
{
    char RxBuff[1024];

    recv(Socket, RxBuff, 1024, 0);
}

Note that the first parameter for select is ignored, i.e. Socket + 1 is just so I know what the select is for!
Ant.

Form view problem

Raghunandan S30-Mar-04 21:19

Raghunandan S

30-Mar-04 21:19

Hi All,

I have a FormView application,which contains some edit boxes ,combo boxes,two radio buttons(radio1 and radio2)and two buttons(button1(IDOK) and button2(IDC_BUTTON_XXX)).

the two buttons have BN_CLICKED handler functions.

when i select radio1, button1 will be shown to the user and button2 will be hidden.
select radio2 ,button2 will be shown to the user and button1 will be hidden.

my problem is that in radio2 selection,i input data in the edit boxes press ENTER key,button1's BN_CLICKED handler function getting invoked instead of button2's handler.

Can anyone tell me what might be the possible reason.

Thanks in Advance..

Re: Form view problem

Antti Keskinen30-Mar-04 21:34

Antti Keskinen

30-Mar-04 21:34

This is caused by the form view's default implementation.

A click on the Enter key issues a command for the form to simulate a click on it's default button, which usually is the 'OK' button. In your case, it is the button 1.

To remedy this, change the button 2 to be the default button of the form, or alternatively, capture keyboard messages sent to the form and filter out those containing VK_RETURN. This prevents the form from calling the default button's BN_CLICKED handler when it receives a key press event indicating the Enter/Return key was pressed.

Of course, when you filter out the keyboard messages, you can custom-call the click handler for the second button as well. To simulate a click on a button, create a WM_COMMAND message, put the HIWORD of wParam to be 'BN_CLICKED' and LOWORD to be the ID of the control. The lParam can be left alone (NULL) or can be the window handle (HWND) of the control.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

How to replicate a directory?

RickardIsraelsson30-Mar-04 21:07

RickardIsraelsson

30-Mar-04 21:07

My problem is to replicate a directory from a server running Windows Server 2003, to a client running Windows XP using Visual C++.
I have search all over to find a solution, but I haven't found any good one. I did find a File Replication Service in Windows Server 2003, but I don't know how to use it.
One solution could be to create a new Replication Service, as I saw here on the code project, but isn't there any existing technique to do this already?

Rickard Israelsson

Re: How to replicate a directory?

David Crow31-Mar-04 2:25

David Crow

31-Mar-04 2:25

Hooking into the File Replication Service would definitely be the way to go as that is what it is for. I would really be surprised if it was not possible. Short of that, I'd search here at CP and Google for some sort of "folder synchronization" utility.

"The pointy end goes in the other man." - Antonio Banderas (Zorro, 1998)

CTreeView

fbachan30-Mar-04 21:03

fbachan

30-Mar-04 21:03

MFC application generated with App wizard has splitter window with two panes, left pane contains CTreeView descendant. I fill tree control with some items, select one item and click on right pane. In this moment tree view does not indicate the selected item. I want tree view to behave like Windows Expolorer - to indicate the selected item, also when it loses focus.
Can anybody suggest a solution?

Frankie

Re: CTreeView

ohadp30-Mar-04 21:36

ohadp

30-Mar-04 21:36

Make sure your tree has this style:

TVS_SHOWSELALWAYS
"Causes a selected item to remain selected when the tree-view control loses focus."

You can do it either through the resource-editor or use 'ModifyStyle' at some initialization point.

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