C / C++ / MFC

17-Oct-07 9:49

Hello
I am writing a class and need a way to catch the exception when some variables are used without being initialized. I'm working in standard c++ but compile it in visual c++ 2005. As far as I can remember I would use this technique in vc6.0:

<br />
if(class_variable==NULL)<br />
//throw the exception

but now i get the compile error: "Run-Time Check Failure #3 - The variable 'class_variable' is being used without being defined. "

I will wait for your answer and would appreciate it.

by regards Shahin Namini

-- modified at 16:10 Wednesday 17th October, 2007

Nemanja Trifunovic17-Oct-07 9:55

Nemanja Trifunovic

17-Oct-07 9:55

shahin namini wrote:
I am writing a class and need a way to catch the exception when some variables are used without being declared.

Declared? Do you mean initialized? Otherwise you would get a compiler error.

shahin namini wrote:
"Run-Time Check Failure #3 - The variable 'class_variable' is being used without being defined. "

Hehe, so even MS people don't know the difference between "defined" and "initialized".

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shahin namini17-Oct-07 10:16

17-Oct-07 10:16

you are right and thanks for notation. The first one was my blunder and i corrected it. anyway have got any idea about my problem?

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C^hris L^osinger17-Oct-07 10:17

C^hris L^osinger

17-Oct-07 10:17

why not just initialize them ?

shahin namini17-Oct-07 10:37

17-Oct-07 10:37

This class does the computations of a 2d ellipsoid, modelling the earth and has lots of variables which are very likely not being initialized. so I thought I would throw the exception whenever i call a function which requires one of the parameters not being initialized yet. have got any comment?

David Crow17-Oct-07 10:44

17-Oct-07 10:44

How would you differentiate between an initialized variable vs. a variable having an invalid value?

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C^hris L^osinger17-Oct-07 10:59

C^hris L^osinger

17-Oct-07 10:59

the is no concept of "uninitialized" built into C++. either you initialize the variables yourself or you live with the effects of random garbage in your program.

just initialize the variables.

David Crow17-Oct-07 10:20

17-Oct-07 10:20

shahin namini wrote:
if(class_variable==NULL)
//throw the exception

If the exception is thrown, that means that class_variable was initialized (to NULL).

shahin namini17-Oct-07 10:40

callbacks in C++: member function pointers / objects

17-Oct-07 10:40

don't care for words. Whatever you call it, I am seeking for the answer!

elmendavies17-Oct-07 8:01

Re: callbacks in C++: member function pointers / objects

17-Oct-07 8:01

Hello,
If I need to use a function in a C library that I can't modify, let's say:

extern "C"
{
void register_callback(void (*callback) (void));
}

... if I also have a class like this:

class MyClass
{
int m_counter;
public:
MyClass() : m_counter(0) {}
void OnEvent()
{
m_counter++;
}
}

Is there any solucion to use MyClass::OnEvent with the funcion register_callback()? In other words, I would like to do something like this (Of course this doesn't work):

int main (void)
{
MyClass my;
register_callback(&(my.MyClass::OnEvent))
}

It's very easy to make MyClass a singleton and define MyClass::OnEvent() as 'static' or use a singleton inside MyClass, which is enough in almost all the cases but I don't want to modify MyClass at all.

I've tried this one:

int main (void)
{
register_callback(sigc::mem_fun(*this,&MyClass::OnEvent));
...
}

That doesn't work. One of the problems is that sig::mem_fun() return an object created in the stack and the parameter for register_callback must be a 'const' one.

Thank you in advance,
Miguel

Jim Crafton17-Oct-07 8:22

Jim Crafton

17-Oct-07 8:22

You can't do this cleanly in C++. I.e. member functions cannot be used where static functions are specified. If you want to hack things and possibly add some cryptic assembler, then it's possible. But that does violate the constraints of the language. There are some articles here on CP that demonstrate this kind of hack if you want to delve into it.

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Re: callbacks in C++: member function pointers / objects

elmendavies18-Oct-07 0:02

Re: callbacks in C++: member function pointers / objects

18-Oct-07 0:02

Thank you Jim, you're right. I have read a lot about this and I haven't find anything useful.

C^hris L^osinger17-Oct-07 8:37

C^hris L^osinger

17-Oct-07 8:37

the callback function doesn't take any parameters ? that sucks.

for this very reason, whenever we do a callback hook in one of our libraries, we specify our that the callback function must take at least one parameter large enough to hold a pointer. for example:

typedef BOOL      (CALLBACK* IS40_SourceCloseFn)(const IS_CALLBACK_DATA uUserInfo);

you can pass a 32-bit value into the 'register callback' function and all the callback calls will pass that parameter back to you. so, you use an object pointer as the 32-bit value, the lib passes that value to the callback function, and you cast it back to the object type in the callback.

otherwise, you're stuck using global variables in the callback (and tricky synchronization schemes to make sure only one call is in there at a time).

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Re: callbacks in C++: member function pointers / objects

elmendavies18-Oct-07 0:12

Re: callbacks in C++: member function pointers / objects

18-Oct-07 0:12

The callback function and MyClass can't be modified. I've make it up so in order to focus the problem.

This is the code that you can't modify:

extern "C"<br />
{<br />
  void register_callback(void (*callback) (void)); /* THIS FUNCTION GIVES YOU ACCESS TO A LIBRARY RUTINE SO I CAN'T MODIFY */<br />
}

... if I also have a class like this:

class MyClass<br />
{<br />
  int m_counter;<br />
public:<br />
  MyClass() : m_counter(0) {}<br />
  void OnEvent() /* NOT STATIC OR CONST */<br />
  {<br />
    m_counter++;<br />
  }<br />
}

Thanks

Stephen Hewitt17-Oct-07 16:44

Stephen Hewitt

17-Oct-07 16:44

elmendavies wrote:
extern "C"
{
void register_callback(void (*callback) (void));
}

Is this the signature of the real callback function? If it takes a context argument (generally void*) then the solution is simple and well known.

Steve

Re: callbacks in C++: member function pointers / objects

elmendavies18-Oct-07 0:17

Re: callbacks in C++: member function pointers / objects

18-Oct-07 0:17

I've make it up. It's not a real library function but it could be. Remember for example the signal function in UNIX and the definition of its callback:

http://www.hmug.org/man/3/signal.php

How to solve it?

Stephen Hewitt18-Oct-07 14:26

Stephen Hewitt

18-Oct-07 14:26

If sizeof(int) is big enough to hold a pointer then something like the following will work.

extern "C" 
{
  void register_callback(void (*callback)(int), int arg);
}
 
class MyClass
{
  int m_counter;
public:  MyClass() : m_counter(0) {}
  void OnEvent()
  {
    m_counter++;
  }
}
 
void MyClassOnEventThunk(int arg)
{
	MyClass *pInstance = reinterpret_cast<MyClass*>(arg);
	pInstance->OnEvent(pInstance);
}
 
// When registering the callback:
MyClass g_inst; // Somewhere.....
register_callback(&MyClassOnEventThunk, reinterpret_cast<int>(&g_inst)); // To register...

If sizeof(int) is ***NOT*** big enough to hold a pointer you will have to maintain a mapping yourself.

Steve

error in splitt, Help

satw1417-Oct-07 6:32

satw14

17-Oct-07 6:32

my project is for grapic in 3 views, when closed program (visual c++ .net 2005, MFC) appear message error.
My project It is called stressinv.

The main window divided into 2 views within one creates two views. Grafico "OnDraw" at each hearing.
At the start of each hearing, uses "CSpritterWnd."

for more details please, written me to satw14@gmail.com.

sorry for my english, but speak spanish.

-------------------------------------------------------

Excepcion no controlada en 0x7821036a (mfc80d.dll) en stressinv.exe:
0xC0000005: Infraccion de acceso al leer la ubicacion Oxfeeefeee.

Re: error in splitt, Help

David Crow17-Oct-07 6:39

Re: error in splitt, Help [modified]

17-Oct-07 6:39

satw14 wrote:
Excepcion no controlada...

An unhandled exception? So what are you doing when the application exits?

satw1417-Oct-07 12:16

satw14

17-Oct-07 12:16

//-MainFrm.cpp
Removed roles created by default and inclusions classes (include).

Here I try to create a view or two panels in the main view.

// CMainFrame construction/destruction

CMainFrame::CMainFrame()
{
// TODO: add member initialization code here
m_wndSplitter=NULL;

}

CMainFrame::~CMainFrame()
{
if (m_wndSplitter != NULL) delete m_wndSplitter;

}

//--Cleft and AreaView These classes are now aggregated
BOOL CMainFrame::OnCreateClient(LPCREATESTRUCT lpcs,
CCreateContext* pContext)
{
m_wndSplitter=new CSplitterWnd();
if(!m_wndSplitter->CreateStatic(this,1,2))return false;
if(!m_wndSplitter->CreateView(0,0,RUNTIME_CLASS(CLeft),CSize(200,200),pContext))return false;
if(!m_wndSplitter->CreateView(0,1,RUNTIME_CLASS(AreaView),CSize(100,100),pContext))return false;
return TRUE;
}

// CMainFrame diagnostics

// when When I finished the program sends the mistake and put me here
#ifdef _DEBUG
void CMainFrame::AssertValid() const
{
CFrameWnd::AssertValid(); //here
}

void CMainFrame::Dump(CDumpContext& dc) const
{
CFrameWnd::Dump(dc);
}

#endif //_DEBUG

thanks David
-- modified at 18:24 Wednesday 17th October, 2007

Re: error in splitt, Help

David Crow17-Oct-07 17:50