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2ASoft wrote: I love you.....in a non-homosexual way.
That was really funny.
Glad it helped.
Cédric Moonen
Software developer
Charting control
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Hi,
I have a class that wraps a COM object and has only 1 member, a pointer to the COM object (interface pointer) and several methods. It could also be any other pointer.
The size of an instance of this class is 4 bytes, there are no virtual methods or other members.
class CIntPtr<br />
{<br />
public:<br />
void AddOne () { (*m_pMyInt)++; }<br />
int *m_pMyInt;<br />
};
Is it now safe to cast an int* to an CIntPtr*?
int myInt = 0;<br />
int *myIntPtr = &myInt;<br />
<br />
CIntPtr *myIntWrapper = (CIntPtr *) &myIntPtr;<br />
myIntWrapper->AddOne ();
The code runs fine and I don't see any problem with this. Actually I would even say it is better than creating a new object and calling the constructor which makes a copy of the pointer. There is also no additional object that needs to be deleted.
But maybe this causes problems I'm not aware of.
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I'm new to C++ (just a question), how can you use *m_pMyInt before you intialize it?
class CIntPtr<br />
{<br />
public:<br />
void AddOne () { (*m_pMyInt)++; } <-------use<br />
int *m_pMyInt; <-------intialize<br />
};
Just wondering.... or am I just stupid?
"C++ will solve any problem."
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#hackC++ wrote: how can you use *m_pMyInt before you intialize it?
Have a look at the other code, I'm 'faking' an object.
Or do you mean declare instead of initialize? It's common practice to have the members at the bottom of the class and the methods at the top.
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You're being too clever for your own good. Casting pointers like that may work, on your current OS and current compiler. There's no guarantee it will work on others or even future versions of your current compiler.
ABuenger wrote: Actually I would even say it is better than creating a new object and calling the constructor which makes a copy of the pointer.
A temporary object of CIntPtr can be created and deleted very quickly. Again, you're being too clever, and besides unless you're creating billions of temp objects, you're not going to see any speed increase on any computer built this century.
--Mike--
Visual C++ MVP 
LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ
VB > soccer
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I agree that this kind of technique should be avoided; but as long as you’re careful it should work on all standard compliant compilers. As long as you don't have any virtual functions the layout will be compatible with that of the member. The layout of a struct or class is predictable and standard for the most part. Certainly for a simple class with no base classes or virtual functions it is.
Steve
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It's not a question of whether it works, it's a question of whether code like that should be written in the first place. If I saw code like that, and I knew nothing else of the author, I'd be highly suspicious of his grasp of C++ basics.
--Mike--
Visual C++ MVP 
LINKS~! Ericahist | PimpFish | CP SearchBar v3.0 | C++ Forum FAQ
VB > soccer
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As I said, "I agree that this kind of technique should be avoided". My comment was motivated by your statement that, "Casting pointers like that may work, on your current OS and current compiler. There's no guarantee it will work on others or even future versions of your current compiler." This need not be the case: the layout of structures in C/C++ is well defined. This is why a struct can be used to write to the registers on a hardware device in device drivers for example. In short, code like the OP's can be made to work portably although in general it should be avoided.
Steve
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This is just another way of exploiting power of pointers provided by C++. But this is not considered as good practice.
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ABuenger wrote: Actually I would even say it is better than creating a new object and calling the constructor which makes a copy of the pointer.
This is an illusion. Firstly note that sizeof(CIntPtr*) == sizeof(CIntPtr). This means that, from a storage point of view, there is no difference. i.e.
class CIntPtr
{
public:
CIntPtr(int *pInt = NULL) : m_pMyInt(pInt) {}
void AddOne () { (*m_pMyInt)++; }
int *m_pMyInt;
};
int myInt = 0;
int *myIntPtr = &myInt;
CIntPtr *myIntWrapper = (CIntPtr*)&myIntPtr;
CIntPtr myOtherWrapper(&myInt);
In short the advantages of this confusing technique may be imagined.
Steve
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Hi all,
Has anyone encountered some VERY STRANGE problems with layered windows, when using the CWnd::UpdateLayeredWindow() API call?
I have had success and failures using the SAME call from within the constructor of my CWnd derived class. My "success" is determined by the classname used when the window was created.
I'm calling UpDateLayeredWindow() this way:
BOOL bResult = UpdateLayeredWindow( NULL, &ptDest, &size, &mem,<br />
&ptSrc, byAlpha, &m_Blend, ULW_ALPHA);
Note "mem" is a screenCompatible CDC, on which a bitmap was drawn via code(simple rectangular fill), and size is the size of the CBitmap object selcted into the mem CDC.
1) Partial success if created using -
CWnd::CreateEx(WS_EX_LAYERED |WS_EX_TOPMOST|WS_EX_TOOLWINDOW, "STATIC",<br />
_T(""),WS_VISIBLE|WS_POPUP, 300,300,200,200,NULL, NULL, NULL );<br />
my window appears, but doesn't receive mouse events.
2) Failure, if I create it using:
CreateEx(WS_EX_LAYERED |WS_EX_TOPMOST|WS_EX_TOOLWINDOW, m_lpszClassName,<br />
_T(""),WS_VISIBLE|WS_POPUP, 300,300,200,200,NULL, NULL, NULL );
where
m_lpszClassName = AfxRegisterWndClass( CS_VREDRAW | CS_HREDRAW | CS_OWNDC );
The bitmap does NOT appear. I have to do a bitblt of the mem to screen to see it appear, preceded by a MoveWindow call. But then I receive mouse events.
I find this baffling. Does anyone else have any insight into this situation?
Thanks for anything info you can provide!
Jeanne Sim
-- modified at 19:22 Thursday 15th June, 2006
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Hello,
When you define in some function a critical section you define a critical section block or variable ?
I will explain - when some thread get to this Critical section and the Critical section is lock - so this thread will go sleep until this Critical section will be unlock and the event will be called to rise up.
But my problem (or my bad understanding) is about the block of the critical section - i think that the critical section is only to block thread and make the thread sleep and have no direct connection to the block - but some other thought is that the critical section is define only on block.
Can someone explain the main idea of the critical section in this case ?
Thanks on any help. 
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There are numerous good articles about this:
Check Here.[^]
----------
Some problems are so complex that you have to be highly intelligent and well informed just to be undecided about them.
- Laurence J. Peters
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yanshof wrote:
Can someone explain the main idea of the critical section in this case ?
See here.
"The largest fire starts but with the smallest spark." - David Crow
"Judge not by the eye but by the heart." - Native American Proverb
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I read those both and i still have the same question.
My question will not appear in there.... like i said this is hard question...
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yanshof wrote: I read those both and i still have the same question.
Why? What part did you not understand?
yanshof wrote: My question will not appear in there....
Maybe not directly, but you can easily infer the answer.
yanshof wrote: When you define in some function a critical section you define a critical section block or variable ?
A critical section is a block of code (that can contain variables).
yanshof wrote: Can someone explain the main idea of the critical section in this case ?
The link I provided you explained this in detail.
"The largest fire starts but with the smallest spark." - David Crow
"Judge not by the eye but by the heart." - Native American Proverb
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yanshof wrote: - i think that the critical section is only to block thread and make the thread sleep and have no direct connection to the block - but some other thought is that the critical section is define only on block.
I'm not sure I follow..
A CRITICAL_SECTION variable is an opaque object which holds a lock state. It's not a handle to anything, like mutexes are (they are kernel objects). I'm not sure what you mean by block, but I'm going to assume it's a body of code such as { ... }. A critical section is not automatically associated with such a block. The state of the critical section object is determined by the Enter/Leave functions, and can span over any number of blocks.
--
100% natural. No superstitious additives.
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A critical section is a small section of code that requires exclusive access to some shared resource before the code can execute. To protect that section of code we need to encapsulate that code in EnterCriticalSection and LeaveCriticalSection function call.
Better avoid using 'block' terminology.
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In MFC-speak that would be a CCriticalSection object along with a CSingleLock object.
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Does anyone know of a way to take an existing VC project and clone it to another directory with a new name. The project file would be re-named, along with the cpp files.
Captain, I must protest, I am NOT a merry man.
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Did menually before, by renaming source files and modifying these project files:
.dsw
.dsp
.rc
These files can be opened and changed in any text editor.
- It's easier to make than to correct a mistake.
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vc provides one method.
build new project, select "Custom AppWizard",input new project name.ok
show "Custom AppWizard - Step 1 of 2", select "an existing Project",
next, show "Custom AppWizard - Step 2 of 2",
now notice select yourself project (*.dsp),finish.
build...
now it will bring "*.awx" and "*.pdb". then copy they to
vc install directory common\msdev98\template.
now you build new project, use "AppWizard", you find new item.
alantop
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Terms:
Ext: Computer which to which I can connect using telnet.
Local: My personal computer.
MyApp: Application which runs on Local.
Problem:
I would like to control an application on Ext. using MyApp running on Local. One way I can think of doing this is to open a command console, CC1 on Local, and telnet into Ext. If I then redirect the input/output from MyApp (running in a second command console, CC2) to CC1, I can accomplish this task. The windows utilities GetStdHandle and WriteConsole look like they could be useful here. I am familiar with C but new to windows programming,
so I don't know if this strategy is a good approach, or perhaps there may be a much better way to accomplish this task (TCPIP server?)
Any suggestions would be appreciated.
Thanks.
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Have you considered Remote Procedure Call (RPC)? There's also Remote Execute (REXEC).
"The largest fire starts but with the smallest spark." - David Crow
"Judge not by the eye but by the heart." - Native American Proverb
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I did not consider RPC, and think this might be a good solution. Am studying this.
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