C / C++ / MFC Discussion Boards

Senkwe Chanda18-Jan-04 11:58

18-Jan-04 11:58

I took this from an online example.

using VC++ 7 if you write...

int StudentAge;<br />
		<br />
		<br />
	cout << "Student age = " << StudentAge << endl;	<br />
		<br />
	cout << endl;<br />

You will (rightly) get a runtime check failure since StudentAge has not been initialized.

What I'd like to know is why THIS works

int StudentAge;<br />
	int* ptrAge;<br />
	<br />
	ptrAge = &StudentAge;<br />
	<br />
	cout << "Student age = " << StudentAge << endl;	<br />
		<br />
	cout << endl;

Here I don't get a runtime check failure even though it's clear StudentAge still hasn't been initialized. I'm just curious as to why this is the case.

Thanks

Woke up this morning...and got myself a blog

Re: Ok, so when is a variable defined?

Gary R. Wheeler18-Jan-04 12:13

Gary R. Wheeler

18-Jan-04 12:13

Neither case should issue a runtime error.

The first case will issue a compiler warning (variable used without being initialized), depending on your compiler options.

The second case is sufficient to mark the variable StudentAge as having been 'touched' (by the & operator), hence the warning wouldn't be appropriate. The compiler isn't (and shouldn't be, IMO) smart enough to look for secondary effects. Perhaps the variable gets initialized as a side effect, via the pointer.

Software Zen: delete this;

Re: Ok, so when is a variable defined?

Senkwe Chanda18-Jan-04 13:01

Senkwe Chanda

18-Jan-04 13:01

Thanks Gary, I used the term "Runtime Check Failure" because that's what the VC++7 warning dialog says (at runtime I might add). I guess I haven't set up my IDE to warn me on such things because the compile in the first case is clean as a whistle Smile | :)

Thanks!!

Woke up this morning...and got myself a blog

Re: Ok, so when is a variable defined?

Gary R. Wheeler18-Jan-04 15:16

Gary R. Wheeler

18-Jan-04 15:16

Hmmm. Is this Managed C++, by any chance? I'm just curious. I write 'unmanaged' C++, and have never seen this behavior at runtime.

Software Zen: delete this;

Re: Ok, so when is a variable defined?

Senkwe Chanda18-Jan-04 17:12

Senkwe Chanda

18-Jan-04 17:12

No it's plain C++ Smile | :)

Using VC++7.

Woke up this morning...and got myself a blog

Re: Ok, so when is a variable defined?

Mike Dimmick18-Jan-04 23:34

Mike Dimmick

18-Jan-04 23:34

From the compiler documentation, /RTC switch:

[quote]
/RTCu

Reports when a variable is used without having been initialized. For example, an instruction that generates C4701 may also generate a run-time error under /RTCu. Any instruction that generates C4700 will generate a run-time error under /RTCu.

However, consider the following code fragment:

int a, *b, c;
if ( 1 )
b = &a;
c = a; // no run-time error with /RTCu

If a variable could have been initialized, it will not be reported at run time by /RTCu. For example, after a variable is aliased through a pointer, the compiler will not track the variable and report uninitialized uses. In effect, you can initialize a variable by taking its address. The & operator works like an assignment operator in this situation.
[/quote]

[edit] Made attribution clearer. [/edit]

Re: Ok, so when is a variable defined?

Senkwe Chanda19-Jan-04 4:42

Senkwe Chanda

19-Jan-04 4:42

Thanks Mike, looks like Gary was right Smile | :)

Woke up this morning...and got myself a blog

A Discrete Mathematic problem.

MaJr18-Jan-04 11:36

MaJr

18-Jan-04 11:36

Hi,
I'm trying to make a program in C++ that calculates and prints all the potential partitions of a group of n elements to groups of k elements (n is a integer multiplicate of k).
For example if n=4, k=2 :
{{a1,a2}, {a3,a4}}
{{a1,a3}, {a2,a4}}
{{a1,a4}, {a2,a3}}
I really need an algorythm about this so if you have a suggestion or if you know any links about Discrete Mathematics Algorythms i would appreciate it.
(Sorry if my English are bad)

Paparia Mantoles!

Re: A Discrete Mathematic problem.

Alexander ^M.,19-Jan-04 2:14

Alexander ^M.,

19-Jan-04 2:14

is this really a math problem?

Don't try it, just do it! Wink | ;-)

Popup menu pops up in wrong place

Daniel132418-Jan-04 11:18

Daniel1324

18-Jan-04 11:18

I derived a class from CListBox. In that class I added a handler for the right mouse button. When I click the right button, the menu pops up on my desktop. I know why its doing this, because the CPoint passed to the function is relative to the whole screen, not my listbox.

I cant figure out how to tell the menu to popup where my mouse is.
I tried ScreenToClient() but it didnt work.

<br />
void CMyListBox::OnRButtonUp(UINT nFlags, CPoint point) <br />
{<br />
	CMenu Menu;<br />
	Menu.LoadMenu(IDR_POPUP_MENU);<br />
	CMenu *Popup = Menu.GetSubMenu(0);<br />
	ScreenToClient(&point);<br />
	Popup->TrackPopupMenu(TPM_LEFTBUTTON|TPM_RIGHTBUTTON|TPM_LEFTALIGN, <br />
		point.x, point.y, this, NULL);<br />
	Menu.DestroyMenu();<br />
}<br />

Anybody help?

Thanks!

Re: Popup menu pops up in wrong place

PJ Arends18-Jan-04 16:31

PJ Arends

18-Jan-04 16:31

The point is given to you in client coords, and TrackPopupMenu() expects screen coords, so use ClientToScreen() to convert the point.

Sonork 100.11743 Chicken Little

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

Within you lies the power for good - Use it!

Re: Popup menu pops up in wrong place

Michael Dunn18-Jan-04 16:31

Michael Dunn

18-Jan-04 16:31

You have two problems. First, the point parameter is in window coords, not screen coords. Second, TrackPopupMenu() takes screen coords for the menu location. So you should call ClientToScreen(&point)

--Mike--
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Re: Popup menu pops up in wrong place

Roger Allen18-Jan-04 23:51

Roger Allen

18-Jan-04 23:51

Or you could just call

::GetCursorPos(&point);

Which will give you the current mouse position in screen coordinates

Roger Allen - Sonork 100.10016
Roger Wright: Remember to buckle up, please, and encourage your friends to do the same. It's not just about saving your life, but saving the quality of life for those you may leave behind...

Re: Popup menu pops up in wrong place

Daniel132419-Jan-04 0:51

Daniel1324

19-Jan-04 0:51

Thanks to all of you. That worked.

Re: Popup menu pops up in wrong place

фил21-Jan-04 4:50

фил

21-Jan-04 4:50

some times MFC drives me so nuts that i use SDK procs.

CPoint cpPoint;
GetCursorPos(&cpPoint);

SetWaitableTimer

Mikey_E18-Jan-04 10:23

Mikey_E

18-Jan-04 10:23

I'm trying to set a waitable timer from a CTime object. So I'm doing converstion from CTime to SYSTEMTIME then to a FILETIME and finally to a LARGE_INTEGER structure so I can pass it to SetWaitableTimer.

This compiles and runs, however my timer fires immediately every time. It's completely ignoring the time to fire on. Am I making these converstions wrong or just completely flubbing the whole thing up? I'm lost, any help would be very appreciated!!

CTime m_tNextRun(Schedule.GetNextRunTime());
// Convert m_tNextRun to a SYSTEMTIME structure
SYSTEMTIME m_st_DueTime;
m_tNextRun.GetAsSystemTime(m_st_DueTime);

// Convert m_st_DueTime to a FILETIME structure
FILETIME m_ft_DueTime;
::SystemTimeToFileTime(&m_st_DueTime, &m_ft_DueTime);

// Copy m_ft_DueTime into a LARGE_INTEGER structure
LARGE_INTEGER m_lg_DueTime;
m_lg_DueTime.LowPart = m_ft_DueTime.dwLowDateTime;
m_lg_DueTime.HighPart = m_ft_DueTime.dwHighDateTime;

// Set the next timer
if(!::SetWaitableTimer(handles[command_timer], &m_lg_DueTime,0, NULL, NULL, 0)) {
// Set timer failed, handle the error
DEBUG_LOG("CSleeperThread::run(): set waitable timer failed.");
}

// suspend until the timer expires
::WaitForMultipleObjects(2, handles, FALSE, INFINITE);

Mike Ellertson

Re: SetWaitableTimer

Mike Dimmick18-Jan-04 23:39

Mike Dimmick

18-Jan-04 23:39

I don't see anything wrong with it. I assume you've already called CreateWaitableTimer?

What's the return value of WaitForMultipleObjects?

Re: SetWaitableTimer

Mikey_E19-Jan-04 10:17

Mikey_E

19-Jan-04 10:17

The return value of WaitForMultipleObjects is the index of the timer(which is what it should be).

If you look at SetWaitableTimer on MSDN the second parameter specifies the alarm date for the timer. Only thing, it's a LONG_INTEGER structure that your supposed to set using the FILETIME format.

I'm pretty sure I'm setting up this format wrong. Does anyone have a good conversion routine from a CTime object to a LONG_INTEGER used by SetWaitableTimer? Or have any advice on setting this FILETIME format?

Re: CSleeperThread

Clem8628-Mar-08 2:45

Clem86

28-Mar-08 2:45

Hello,
About your article with the CSleeperThread's class and the functions :
static VOID CALLBACK TimerProc_Wrapper
VOID CALLBACK TimerProc
void ThreadMain();
void WakeUp();

How do you use those functions in the main in order to suspend the thread for 10s for example?
Thanks
Clément, french student

Can My Window Receive Messages

bitpusher18-Jan-04 9:40

bitpusher

18-Jan-04 9:40

Hello,

I'm trying to *Send* a message to a Dialog Bar window early on in the initialization of an app and I believe I'm crashing because the Dialog Bar has not been created yet. How can I test to ensure it's been created and can accept & process such messages? I try to get a safe Handle (or call GetActiveWindow()), but that's valid all the time. If I change the SendMessage to a PostMessage, everything works, but I do need a SendMessage for some execution timing later in the app. Any suggestions/help?

thanks! JennyP

<code>
........
CDiagGlobalSched *gl_sched = &(((CMainFrame *)AfxGetApp()->m_pMainWnd)->m_SchedDlgBar1);

if (ForceUpdate) {
	if (gl_sched->GetActiveWindow() != NULL) { // passes this test, then errors on the next line.
		gl_sched->SendMessage(WM_COMMAND, ID_UPDATE_SCHED_BAR);
	}
	return TRUE;
}
</code>

structs

[Anders]18-Jan-04 8:53

[Anders]

18-Jan-04 8:53

say i have a struct like this:

<br />
<br />
typedef struct {<br />
 char* text1;<br />
 char* text2;<br />
 ...<br />
 char* text25;<br />
}MYS,*PMYS;<br />

how can i access the struct like this?

<br />
PMYS pS=SomehowGetPtrToStruct();<br />
for (int i=0; i < MYS_TEXTCOUNT; i++)<br />
{<br />
char* text=pS[i];<br />
dosomething(text);<br />
}<br />

i dont want to get the items like this:

char* text=pS->text2;<br />

i also tried to do stuff like: char* text=pS+(sizeof(char*)*i); but i cant get it to work Confused | :confused:

Re: structs

markkuk18-Jan-04 10:18

markkuk

18-Jan-04 10:18

If you want to use the array syntax, use an array (or a std::vector). You could overload the [] operator for your struct if you want to obfuscate your code.

Re: structs

[Anders]18-Jan-04 11:23

[Anders]

18-Jan-04 11:23

i dont need to use the array syntax, i just need to access the members of the struct without using the names

Re: structs

Ian Darling18-Jan-04 11:30

Ian Darling

18-Jan-04 11:30

[Anders] wrote:
i dont need to use the array syntax, i just need to access the members of the struct without using the names

But that's exactly what you want to do Confused | :confused:

ps[i] = use of array syntax

--
Ian Darling
"The moral of the story is that with a contrived example, you can prove anything." - Joel Spolsky

Message Closed

18-Jan-04 11:37

[Anders]

18-Jan-04 11:37

Message Closed

modified 20-Feb-22 19:24pm.

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