C / C++ / MFC

Re: linked list adding operation with two structure type

30-Apr-11 4:22

Sure it goes wrong, as this statement

while ( (*list)->current != NULL ) (*list)->current = (*list)->current->fn_next;

is bound to result in (*list)->current being zero/null, hence the following

(*list)->current->fn_next=...

will bomb.

Some ideas:

1.
if you want to add a node at the end of the list, and your data structures have a tail member, why not use it, rather than scanning the list?

2.
try not to have special cases. When done properly, one often does not need them. And when one does, try making the alternate paths as short as possible, they tend to have common things (such as return, and count++ of which you forgot one).

Smile | :)

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quartaela30-Apr-11 5:13

Re: linked list adding operation with two structure type

30-Apr-11 5:13

i changed my way to implement the linked list with only NODE structure which is the way i know well. but this fault is not acceptable for me, i am angry to myself now because i want implement to list with using LIST structure. anyway, could you explain why i can't print the data with using code like this --> list->head->first_name

Luc Pattyn30-Apr-11 5:36

Re: linked list adding operation with two structure type

30-Apr-11 5:36

I did not tell you to drop the LIST structure; if you want new nodes added at the tail, having a tail pointer is the obvious way of doing it, as it is much faster than searching for the last node each time.

And your original code would never reach the print statement as it bombs when you use the null reference that is the resulting of spinning the while loop. So either use the tail pointer and drop the while loop, or fix the while loop.

Smile | :)

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Andrew Phillips30-Apr-11 5:17

Andrew Phillips

30-Apr-11 5:17

This is obviously an assignment but I'll give you some ideas.

a. It's better to use an existing container like std::list but if this is C and you don't have one or you have to write your own linked list then ...

b. You don't need to store current. I also assume you store tail and count for efficiency as you can work these out too.

c. You store tail but then in add_Node() you scan the list for the end anyway.

d. It may be simpler just to add new students to the start of the list rather than the end.

NODE * tmp = head;
head = student;
student->next = tmp;

e. If you step through your code the bvious problem is assigning through a NULL pointer. Why not do it like this:

void add_Node(LIST** list, NODE* student)
{
     NODE ** pcurr;
     for (pcurr = &head; *pcurr != NULL; pcurr = &((*pcurr)->next) )
         ;  // no loop body
     *pcurr = student;
     student->next = NULL;
 }

Andrew Phillips
http://www.hexedit.com
andrew @ hexedit.com

Re: linked list adding operation with two structure type

quartaela30-Apr-11 5:35

Re: linked list adding operation with two structure type

30-Apr-11 5:35

hi andrew;

firstly, i must create my own linked and i know how to create it and i know how to make some simple operations with linked list. but this is the first time i want to use LIST structure(as you can see there is a head,tail,current and count). for example i wanna use like this;

list->head->first_name

and logically isn't it true_?. in main function the code is work well if i use like this

printf("%s\n", student->first_name );

but if use like this it isn't working. so what is the difference_?.

printf("%s\n", list->head->first_name );

Andrew Phillips30-Apr-11 5:59

Andrew Phillips

30-Apr-11 5:59

> printf("%s\n", list->head->first_name );

Yes, this should work. It could be that list or list->head are NULL or uninitialised.

Try:
printf("%p %p %s\n", list, list->head, list->head->first_name );

which will print out the values of the pointers. Or step through the code and look at the values in the debugger.

Andrew Phillips
http://www.hexedit.com
andrew @ hexedit.com

Re: linked list adding operation with two structure type

Luc Pattyn30-Apr-11 6:10

Re: linked list adding operation with two structure type

30-Apr-11 6:10

Andrew Phillips wrote:
printf("%p %p %s\n", list, list->head, list->head->first_name );

I guess one needs separate print statements here, as if one argument bombs, nothing will be printed at all.

Smile | :)

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quartaela30-Apr-11 8:03

Re: linked list adding operation with two structure type

30-Apr-11 8:03

i opened another project to implement the list with LIST and NODE structure. but i am facing with an error. i couldn't fix it.
the error is;
expected '=', ',', ';', 'asm' or '__attribute__' before '*' token

and the error is in create_list function which is;

LIST* create_list(void)
 {

    LIST* list;

    list = (LIST*) malloc(sizeof(LIST));

    if (!list) {

        printf("ERROR NOT ENOUGH MEMORY!!!\n");
        exit(100);
    }

    else {

        list->count = 0;
        list->current = NULL;
        list->head = NULL;
        list->tail = NULL;

    }

    return list;

}

and this is the main function;

LIST* create_list(void);

int main( void ) {

    LIST* list;

    list = create_list();

    build_list(list);

    print_list(list);

    return 0;
}

Luc Pattyn30-Apr-11 8:10

Re: linked list adding operation with two structure type

30-Apr-11 8:10

most compilers give file name (and/or class name) and line number; tell your IDE to always show line numbers in editor windows. And try double-clicking the error message, any of these measures should bring you right to the objectionable statement.

BTW: Did you provide the definition of NODE and LIST before referencing them in your source code?

Smile | :)

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quartaela30-Apr-11 8:16

Re: linked list adding operation with two structure type

30-Apr-11 8:16

i can see the location of error when i double clicked Big Grin | :-D

.

this is the line which error appears in create_list.h

LIST* create_list(void)

quartaela30-Apr-11 8:20

Re: linked list adding operation with two structure type

30-Apr-11 8:20

well i solved the problem. and this is the most stupid problem i have ever faced. it takes for hours to see. i only changed the location include "structures.h" with include "create_list.h" Big Grin | :-D

. so know create_list function can realize the structures Smile | :)

Luc Pattyn30-Apr-11 8:32

Problem in Callback function in Client Application [modified]

30-Apr-11 8:32

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manoharbalu30-Apr-11 1:27

manoharbalu

30-Apr-11 1:27

I have created a test client application using WTClient.DLL to connect to matrikon OPC Server demo version. The WTClient.DLL has functions to interface the client application with the OPC Server. The client application basically exchange values with the server by creating the server tags (variables). The WTClient.DLL has callback functions used to update the client application tags with values from the server.

When there is an update of any of the value in the created tags the Matrikon OPC server issues callback to the client using the WTClient.DLL. Using the Callback function I update the changed values. However during sometimes after connecting my client application with the server, the callback does not happen even there is a change in the server data.

The code is as follows:

void CALLBACK EXPORT OPCUpdataCallback (HANDLE hGroup, HANDLE hItem, VARIANT *pVar, FILETIME timestamp, DWORD quality)
{
//Call to my function for updating the values (pVar) using the Handle hItem.
}

When I reopen my Client Application, it works fine. Again during sometimes the problem comes and so my application becomes unreliable.

Anybody Kindly help me to find out why my callback is not called from the server. My server is a standard application which is not supposed to have any errors

modified on Saturday, April 30, 2011 7:49 AM

Re: Problem in Callback function in Client Application

Hans Dietrich30-Apr-11 4:27

Hans Dietrich

30-Apr-11 4:27

Since this is an intermittent problem, it might be hard to track down. You need to strip down your client to the smallest possible app, that demonstrates this problem. Does the matrikon OPC Server come with source code for a demo client? If so, does that demo exhibit the problem? Again, try to boil it down to the smallest possible app. It is also very important to check the return codes of all functions, to see if there is an error.

If none of this works out, then check if there is a user forum for matrikon OPC Server. It might be something simple, which can be answered quickly.

Finally, of course, you could simply send an email to the vendor (I'm assuming matrikon OPC Server is a commercial product).

Best wishes,
Hans

[Hans Dietrich Software]

Is there any way to SendMessage to a Button control

lamparded30-Apr-11 1:27

Re: Is there any way to SendMessage to a Button control

30-Apr-11 1:27

Just SendMessge to the Button IDC_BUTTON1 and make sure the button will be clicked

what's the code ?

thanks for help!

«_Superman_»30-Apr-11 2:12

«_Superman_»

30-Apr-11 2:12

If you're not using MFC, the following would be the code, where hDlg is the handle to the dialog hosting the button -

::SendMessage(hDlg, WM_COMMAND, (BN_CLICKED << 16) | IDC_BUTTON1, ::GetDlgItem(hDlg, IDC_BUTTON1);

If you're using MFC, the following would be the version if you're calling it from within the dialog class -

SendMessage(WM_COMMAND, (BN_CLICKED << 16) | IDC_BUTTON1, GetDlgItem(IDC_BUTTON1));

«_Superman_»
I love work. It gives me something to do between weekends.

Microsoft MVP (Visual C++)

Polymorphism in C

Re: Is there any way to SendMessage to a Button control

lamparded30-Apr-11 3:27

Re: Is there any way to SendMessage to a Button control

30-Apr-11 3:27

ERROR,parameter 3...

SendMessage(WM_COMMAND, ((WPARAM)BN_CLICKED)<<8|(WPARAM)IDC_BUTTON, 0L); is that right?

I want the Button will be clicked down when the Message send,but there's nothing happened with the Button while the Message sent ,why

Hans Dietrich30-Apr-11 4:18

Hans Dietrich

30-Apr-11 4:18

If you want to emulate a human pressing a button, then you will have to perform the actions a human performs:

1. Press button: send WM_LBUTTONDOWN

2. Hold button down a while: use SetTimer() or similar to implement delay.

3. Release button: send WM_LBUTTONUP.

Best wishes,
Hans

[Hans Dietrich Software]

Re: Is there any way to SendMessage to a Button control

Richard MacCutchan30-Apr-11 5:33

Richard MacCutchan

30-Apr-11 5:33

Why did you not use the code that Superman posted? Re-read his answer and select the appropriate one (MFC or non-MFC) and use copy & paste to add to your project.

The best things in life are not things.

Re: Is there any way to SendMessage to a Button control

lamparded30-Apr-11 6:18

Re: Is there any way to SendMessage to a Button control

30-Apr-11 6:18

I got a error with it in my MFC app
Error 1 error C2664: 'CWnd::SendMessageW' : cannot convert parameter 3 from 'CWnd *' to 'LPARAM'

Richard MacCutchan30-Apr-11 6:51

Richard MacCutchan

30-Apr-11 6:51

Just use a cast thus:

SendMessage(p1, p2, (LPARAM)p3 ...

You should really study and understand these basics of C++ before embarking on advanced projects such as you describe.

The best things in life are not things.

Re: Is there any way to SendMessage to a Button control

lamparded30-Apr-11 13:31