C / C++ / MFC

How to handle WM_NCLBUTTONUP in my window.

13-Aug-07 20:35

Hello everyone,

I am using Visual Studio 2003. I am writing a JNI program, and upper layer is Java code and lower layer is C code (DLL). The Java code is utilizing C code by JNI.

To debug the C code, in the C DLL Project Properties dialog, I assign Debugging Command to java, then set Command argument to,

-classpath "C:\Program Files\Java\jdk1.5.0_06" HelloWorld,

when when debugging from Visual Studio, Visual Studio will crash. Do you know anything wrong with the settings?

I have also tried to run manually from command line,

java -classpath "C:\Program Files\Java\jdk1.5.0_06" HelloWorld

and the result is correct.

regards,
George

ss43113-Aug-07 19:13

ss431

13-Aug-07 19:13

hiiii,

I want to handle WM_NCLBUTTONUP in my doc/view application. I already add this message handler for my window. But it was not responded when my mouse was up in the caption bar of my window.Please give suggestion for how to handle the WM_NCLBUTTONUP?

Thanks in advance...

ss

Re: How to handle WM_NCLBUTTONUP in my window.

Iain Clarke, Warrior Programmer13-Aug-07 22:36

shutdown system on a particular time using vc++

13-Aug-07 22:36

First thing I would do is handle (at least as a test) WM_NCLBUTTONDOWN. Its quite possible that something is grabbing the down button, and then capturing the mouse until an UP comes along, bypassing you.

If you can't see the DOWN message, then you've probably not added the handler properly.

Another possibility...

The view itself doesn't actually *have* a caption bar - its provided by the CChildFrame in a non-maximised MDI frame, or the CMainFrame in a SDI app, or a maximised view. So you may be subclassing the wrong window!

Iain.

p_13-Aug-07 19:06

13-Aug-07 19:06

hi all masters of vc
i want to know that how can i automaticlly
shutdown and logon system on a particular time in vc++
please help me
thanks Rose | [Rose]

Re: shutdown system on a particular time using vc++

Hamid_RT13-Aug-07 19:58

Hamid_RT

13-Aug-07 19:58

You can use of WM_TIMER and after a time use of ExitWindowsEx.

WhiteSky

array -- foo, &foo and &foo[0]

George_George13-Aug-07 18:36

13-Aug-07 18:36

Hello everyone,

I think if we define foo as char array, for example,

char foo [32];

then foo, &foo and &foo[0] should be the same, right?

For example, the following 3 statements are the same,

strcpy (foo, goo);
strcpy (&foo, goo);
strcpy (&foo[0], goo);

Any comments?

I am very interested in how C treats foo and &foo and make them the same?

thanks in advance,
George

jimfisher13-Aug-07 18:55

13-Aug-07 18:55

I think that you will find this to be compiler dependent.

foo is the array, so C/C++ treats the array name as a pointer to the array and thus it is a pointer of the same value as &foo[0].

With some compilers however, I have seen where the compiler stores a pointer to the array (like &foo[0] and then &foo is a pointer to that pointer... so I would stay away from this syntax.

Jim

George_George13-Aug-07 20:04

13-Aug-07 20:04

Thanks Jim,

I have tested that on Visual Studio, foo and &foo are the same. I think you mean on some other compiler, they may be different.

Here is my test program in Visual Studio.

<br />
int main (int argc, char** argv)<br />
{<br />
        char foo [1024];<br />
        unsigned int p;<br />
        unsigned int q;<br />
        p = foo;<br />
        q = &foo;<br />
<br />
        return 0;<br />
}<br />

I am interested in the cases when "&foo is a pointer to that pointer". I am wondering what is wrong if I still treat foo and &foo the same in this situation? Could you provide more information and analysis please?

regards,
George

jimfisher14-Aug-07 5:45

14-Aug-07 5:45

I do not recall where I have seen it. It was several years ago on an embedded compiler... seems like green hills or perhaps wind river. If you are using microsoft, I don't think you will have a problem treating foo and &foo as equals.

Jim Fisher

George_George14-Aug-07 16:11

14-Aug-07 16:11

Thanks all the same, Jim.

regards,
George

Iain Clarke, Warrior Programmer13-Aug-07 22:46

13-Aug-07 22:46

I was a little intrigued by your question, and made up a little test...

UINT p, q;

char foo [100];

p = (UINT)foo;
q = (UINT) (&foo);

ASSERT(p == q);

char *bar = foo;

p = (UINT) bar;
q = (UINT) (&bar);

ASSERT(p == q);

And you were indeed right. foo and &foo were the same value, but bar and &bar were not. Part of the problem is that we're both cheating and looking at the variables as raw numbers (which I find useful to do conceptually), but the compiler has the advantage of looking at them knowing there type.

So foo is a number, but is known to be an array, while &foo happens through an implementation detail you can't rely on to be true on another day of the week to be the same number, but is treated differently as it has a different type (pointer to an array).

Hard casting like you did can be useful, but it can also be dangerous.

Short answer: compiler dependent. If you rely on it, prepare to be shot in the foot.

Iain.

George_George13-Aug-07 23:23

13-Aug-07 23:23

Thanks Iain,

So, the best practice is not to use &foo? Smile | :)

regards,
George

Iain Clarke, Warrior Programmer13-Aug-07 23:36

13-Aug-07 23:36

There's nothing wrong with using &foo - but not as a number. Use it as a "pointer to an array" and let the compiler worry about location details.

"Is it wrong to do..." is not something I can possibly answer in the general case.

But taking your strcpy example...

char foo [100];

strcpy (foo, "iain");   is fine
strcpy (&(foo[0]), "iain"); is fine, but ugly
strcpy (&foo, "iain"); is syntactically wrong, and I'm surprised you don't get a warning at least. It just happens to work on this compiler.


char *bar = new char [100];

strcpy (bar, "iain");   is fine
strcpy (&(bar[0]), "iain"); is fine, but ugly
strcpy (&bar, "iain"); will fail - and mostlikely crash stuff.

As you see, the only difference between "getting away with it", and "failing" is what's written a few lines up, relying on &array == array is a really bad idea, even if you will always get away with it. Imagine you come back in 3 years, your boss says "this needs to be longer - make it dynamically sized", and your code will crash with you being puzzled.

Iain.

George_George13-Aug-07 23:50

Disabling shortcut in Visual C++ [modified]

13-Aug-07 23:50

Great comments, thanks Iain!

regards,
George

jimfisher13-Aug-07 18:15

Re: Disabling shortcut in Visual C++

13-Aug-07 18:15

In C code an if statement such as:
if(A || B)
will shortcut, i.e. if A is true, it will branch and not even check B.

On the other hand in the case of:
if(A && B)
a shortcut branch is taken if A is false and B is not even checked.

While this is often useful, I have a situation where I would like to disable shortcuts. Is this possible in VC++?

Jim Fisher

-- modified at 0:35 Tuesday 14th August, 2007

Iain Clarke, Warrior Programmer13-Aug-07 22:56

Re: Disabling shortcut in Visual C++

13-Aug-07 22:56

Its pretty deep in the assumptions of C that you will have this shortcutting behaviour, and as you mention, is very useful.

ie.

if (pointer && pointer->otherpointer)
{
   ...
}

would crash if pointer was null, and there wasn't this shortcutting behaviour.

I'm assuming that A and B are complex expressions, or function calls.

In which case you can do...

BOOL A = Something_I_Insist_On_Being_Done ();
BOOL B = Other_Thing ();

if (A || B)
{
   ...
}

If a compiler flag did exist then you'd have terrible trouble understanding why you used it when you look back in two years time. To avoid that, you'd end up writing so many comments you may as well have done the preconditions early as I did in my example.

Iain.

ps. Never forget the impact on your successor - especially as that may be you on a monday morning with a hangover...

David Crow14-Aug-07 3:12

David Crow

14-Aug-07 3:12

It's called short-circuit evaluation, and has been part of C for decades. Why would you want to "disable" it?

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Re: Disabling shortcut in Visual C++

jimfisher14-Aug-07 5:20