Re: Access Violation problem - C / C++ / MFC Discussion Boards

Re: Access Violation problem

Jonathan [Darka]27-Jul-07 0:02

Jonathan [Darka]

27-Jul-07 0:02

What is the return value from the mysql_query(myDB,"select * from login")) function ?

Change it to this for a test:

int i = mysql_query(myDB,"select * from login");

What is the value of i ?

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_27-Jul-07 0:09

27-Jul-07 0:09

sir return value for
int i = mysql_query(myDB,"select * from login");
and i shows value 1 when use debugger

Re: Access Violation problem

Jonathan [Darka]27-Jul-07 0:24

Jonathan [Darka]

27-Jul-07 0:24

Add the try/catch block that Shouvik suggested, it should help diagnose the problem.

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_27-Jul-07 0:40

27-Jul-07 0:40

thanks a lot sir
u have devoted a lot of time for me
thanks a lot

Re: Access Violation problem

Jonathan [Darka]27-Jul-07 0:41

Jonathan [Darka]

27-Jul-07 0:41

No problem, just trying to help a fellow coder.

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

Shouvik Das27-Jul-07 0:06

Shouvik Das

27-Jul-07 0:06

Surround the code for retrieving with a try and catch. then get the error reason by catching the Exception object throught the method what();

I think Jonathan is right. The recordset value is NULL and hence throws an Acess Violation Error

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Re: Access Violation problem

p_27-Jul-07 0:35

27-Jul-07 0:35

sir thnaks
but i dont know about the what(); function
so can u help me sir
thanks

Re: Access Violation problem

Shouvik Das27-Jul-07 0:45

Shouvik Das

27-Jul-07 0:45

Actually I'm not well versed with ODBC section in VC 6.0 So I m just givin u a generalized concept.
Whenever you surround any code with try catch you throw an exception which is the Object of CException Class.

try
{
//Ur record retrieval code goes here

//On error u write a logic to throw an exception object

}
catch(CException e)
{
 MessageBox(e.what()); // will contain the error message
}

So this way you can atleast trace what error are u getting.

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Re: Access Violation problem

p_27-Jul-07 1:06

27-Jul-07 1:06

sir what() is not working with this
it will give error
'what' : is not a member of 'CException'
please sir solve this
thanks

Re: Access Violation problem

Jonathan [Darka]27-Jul-07 1:07

Jonathan [Darka]

27-Jul-07 1:07

Change the code to this:

int i;
MYSQL *myDB = NULL;
MYSQL_RES *res = NULL;
MYSQL_ROW row;
CString user,pass,aqp;

try
{
    if((myDB = mysql_init((MYSQL*) 0)) &&
    mysql_real_connect(myDB,"localhost","root",NULL,NULL,3306,NULL,NULL))
    {
        if(mysql_select_db( myDB,"gourav"))
        {
            GetDlgItemText(IDC_USER,user);
            GetDlgItemText(IDC_PASS,pass);

            if(mysql_query(myDB,"select * from login"))
            {
                res=mysql_store_result(myDB);
                if(res)
                {
                    row = mysql_fetch_row(res);
                    if(row != FALSE)
                        MessageBox(row[0]);
                }
            }
        }
        else
            MessageBox("Can't connect !\nPlease try later.") ;

        mysql_close(myDB);
}
catch(CException& e)
{
    MessageBox(e.what()); // will contain the error message
}

do you get a messagebox with a description of the error in it ?

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_27-Jul-07 1:18

27-Jul-07 1:18

no messagebox sir
because what() is not working with this
it will give error
'what' : is not a member of 'CException'
thanks

Re: Access Violation problem

Jonathan [Darka]27-Jul-07 1:25

Jonathan [Darka]

27-Jul-07 1:25

Change what() to ReportError()

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_27-Jul-07 1:40

27-Jul-07 1:40

hi try this
catch(CException& e)
{
MessageBox(e.ReportError());
}
but gives this error
'MessageBoxA' : cannot convert parameter 1 from 'int' to 'const char *'

Re: Access Violation problem

Shouvik Das27-Jul-07 1:43

Shouvik Das

27-Jul-07 1:43

you will find in my previous post how to get the error into the char err[255].

now pass this as

MessageBox(err);

I hope this works for you fine now

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

<font colour=orange>Re: Access Violation problem</font>

Shouvik Das27-Jul-07 1:38

Shouvik Das

27-Jul-07 1:38

virtual BOOL GetErrorMessage(LPTSTR lpszError,UINT nMaxError,PUINT pnHelpContext = NULL);

Sorry if it is not working. use the above function...the lpszError will containt the error message.

you can have the a

char err[255];
exp_obj.GetErrorMessage(err,255);

hope u get my point

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Debug Assertion error

Anu_Bala26-Jul-07 18:21

Anu_Bala

26-Jul-07 18:21

I got assertion error when im starting the application. it show me the error at Application class(GUSapp.cpp)
CMainFrame* pMainFrame = new CMainFrame;
if (!pMainFrame->LoadFrame(IDR_MAINFRAME))
Whe i debug it,particularly the error occurs at the line
int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
{
if (CMDIFrameWnd::OnCreate(lpCreateStruct) == -1)

At this line assertion error occurs and it debug library shows File:Winmdi.cpp,Line:139.

Why this error occur? My applcation is MDI application and im working in MFC.

Anu

Re: Debug Assertion error

Roger Broomfield26-Jul-07 20:15

Roger Broomfield

26-Jul-07 20:15

The short answer is: because your menu doesnt have enough items in it.

CMDIFrameWnd::OnCreate() attempts to guess which sub-menu is the Window menu. It does this based on the assumption that you have followed the Windows user interface guidelines and have a Help menu as the right-most item and a Window menu immediately to the left of that. The assertion you are getting is specifically because the menu you have made for IDR_MAINFRAME has less than 2 items.

Re: Debug Assertion error

Anu_Bala26-Jul-07 21:10

Anu_Bala

26-Jul-07 21:10

OK. But i need only one menu for my application and specially i dont want help menu and file,view etc.,
I added a one new menu in IDR_MAINFRAME as Operator Station,thats all. This is enough for me.
IS there anyway to overcome this error?

Anu

Re: Debug Assertion error

Roger Broomfield26-Jul-07 22:19

Roger Broomfield

26-Jul-07 22:19

I think before anything else you should read and understand all the functionality of CMDIFrameWnd Class[^] and perhaps review the Win32 MDI documentation[^]

Then you might replace your OnCreateClient with this

BOOL CMainFrame::OnCreateClient(LPCREATESTRUCT lpcs, CCreateContext* pContext) <br />
{<br />
 CMenu* pMenu = NULL;<br />
 if (m_hMenuDefault == NULL)<br />
 {<br />
  pMenu = GetMenu();<br />
  ASSERT(pMenu != NULL);<br />
  pMenu = pMenu->GetSubMenu(0);<br />
  ASSERT(pMenu != NULL);<br />
 }<br />
<br />
 return CreateClient(lpcs, pMenu);<br />
}

That will append the window list to your single Operator Station menu, you might also need to override other member functions of CMDIFrameWnd such as GetWindowMenuPopup which expects to find a standard window menu.

Alternately you could add a standard Window menu after Operator Station and replace your OnCreateClient with this

BOOL CMainFrame::OnCreateClient(LPCREATESTRUCT lpcs, CCreateContext* pContext) <br />
{<br />
 CMenu* pMenu = NULL;<br />
 if (m_hMenuDefault == NULL)<br />
 {<br />
  pMenu = GetMenu();<br />
  ASSERT(pMenu != NULL);<br />
  pMenu = pMenu->GetSubMenu(1);<br />
  ASSERT(pMenu != NULL);<br />
 }<br />
<br />
 return CreateClient(lpcs, pMenu);<br />
}

this is the way I would do it, if I really had to leave out the help menu, as it reduces the number of member functions that you might have to override.

Personally I would include the standard Window menu and a simple Help menu with just an about box.

Re: Debug Assertion error

Anu_Bala26-Jul-07 23:10

Anu_Bala

26-Jul-07 23:10

Yes, It works.I includeed OnCreateClient() and it works fine.

Anu

Re: Debug Assertion error

Anu_Bala26-Jul-07 23:18

Anu_Bala

26-Jul-07 23:18

It works fine. But i cannot close,minimize,maximize the mainframe as well as child window.Even i have buttons for all this.
Whats the problem in that?Pls help me.

Anu

Re: Debug Assertion error

Roger Broomfield26-Jul-07 23:35

Roger Broomfield

26-Jul-07 23:35

Not sure where to start with this. Do you get any messages in the Output window when you debug the application and try to close,minimize,maximize the mainframe or child windows ?

Re: Debug Assertion error

Anu_Bala27-Jul-07 0:22

Anu_Bala

27-Jul-07 0:22

the output windows shows like this..but no repsonse when i click close or minimize button.
SENDING command id 0x8032 to CMainFrame target.
GUS: PumpMessage: hwnd=0x9F03C4, msg = WM_TIMER (0x0000, 0x00000000)
GUS: WndProc: hwnd=0x9F03C4, msg = WM_TIMER (0x0000, 0x00000000)
GUS: PumpMessage: hwnd=0x7F0376, msg = 0x0373 (0x0000, 0x00000000)
GUS: WndProc: hwnd=0x7F0376, msg = 0x0373 (0x0000, 0x00000000)
GUS: WndProc: hwnd=0x9F03C4, msg = WM_IDLEUPDATECMDUI (0x0001, 0x00000000)
GUS: WndProc: hwnd=0x3C02C4, msg = WM_IDLEUPDATECMDUI (0x0001, 0x00000000)
GUS: WndProc: hwnd=0x35038C, msg = WM_IDLEUPDATECMDUI (0x0001, 0x00000000)
GUS: WndProc: hwnd=0x3C02C4, msg = WM_IDLEUPDATECMDUI (0x0001, 0x00000000)
....Like this only.
Actually we using this application without any frame i.e., we use without any close buttons and minimize and maximize button.
For that we change the code precreatewindow in both mainframe and childframe.
But now we need all windows with these buttons.So i commented the cs Style in precreatewindow in both frames.So i get the buttons but it does not work. Particularly if it is restore position,i can mimimize it. But when i maximize it, i cannot do anything.When i click in that button no clicking action takes place.it just sit as it is.I have OnClose() in CMainframe().But when i close the button it does not move to Onclose() function.

Anu

Re: Debug Assertion error

Roger Broomfield27-Jul-07 0:57

Roger Broomfield

27-Jul-07 0:57

Does your CMainFrame have its own OnSysCommand() handler?
If so does it call that base class OnSysCommand()?

Re: Debug Assertion error

Anu_Bala27-Jul-07 1:34

Anu_Bala

27-Jul-07 1:34

My CMainFrame() don't have OnSysCOmmand function.
I made some sample application in MDI.
But there we dont use OnsysCommand(), but every buttons work perfectly it gets minimized,maximized etc.,
My application also MDI application. Then why this problem?
Really i confused why this problem particularly occur in my application.
Even again i started from the scratch,selectin all project settings and added my class codings.But no use.The same problem exists.

Anu

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