Question on strict-aliasing - C / C++ / MFC Discussion Boards

CPallini12-Aug-09 2:38

12-Aug-09 2:38

You're right: there could be valid reasons, anyway you're very (and, of course, politely) curious about her reason.
Roll eyes | :rolleyes:

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.

This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke

[My articles]

Re: Thread

Rajesh R Subramanian12-Aug-09 2:45

Rajesh R Subramanian

12-Aug-09 2:45

Of course, politeness is guaranteed (or 100% money back), after Mr. Maunder's new commandment. Smile | :)

It is a crappy thing, but it's life -^ Carlo Pallini

Re: Thread

CPallini12-Aug-09 3:28

CPallini

12-Aug-09 3:28

BTW there's a polite way to advice someone to stop using threads? Roll eyes | :rolleyes:

modified on Wednesday, August 12, 2009 10:59 AM

CWebBrowser - OnWindowClosingBrowser Method..

Member 383463011-Aug-09 23:44

Member 3834630

11-Aug-09 23:44

I have a dialog based application with WebBrower control on it.

The URL that i open in the webbrowser uses script having Windows.close() method.

When the URL is closing it calls OnWindowClosing Browser Method, and later post a message saying "The webpage you're viewing is trying to close this window. Do you want to close this window? - YES/NO"

My issue is on clicking YES the dialog is not closing.
What should i do to close the dialog on selecting YES in above dialog.

And secondly, i want the application to return 22 on clicking YES. How to may Dialog application return 22 on clicking YES above.

Thank you..

Re: CWebBrowser - OnWindowClosingBrowser Method..

Bacon Ultimate Cheeseburger12-Aug-09 20:10

Bacon Ultimate Cheeseburger

12-Aug-09 20:10

Member 3834630 wrote:
My issue is on clicking YES the dialog is not closing.

After the browser control is closed are you relaying that event to the dialog or attempting to close the dialog with a call to EndDialog()?

1300 calories of pure beef goodness can't be wrong!

Re: CWebBrowser - OnWindowClosingBrowser Method..

Member 383463012-Aug-09 22:29

Member 3834630

12-Aug-09 22:29

Hello,

I have not done anything currently.
What should i do to get dialog closed when Windows.Close() method is called in script.
What to do to close the dialog when YES is selected and return a different value to ExitInstance().

Thank you..

Re: CWebBrowser - OnWindowClosingBrowser Method..

Bacon Ultimate Cheeseburger12-Aug-09 23:03

Bacon Ultimate Cheeseburger

12-Aug-09 23:03

Member 3834630 wrote:
What should i do to get dialog closed when Windows.Close() method is called in script.

It really depends on your requirements. One way would be to create a class that implements the DWebBrowserEvents2[^] dispatch interface and register it with the appropriate connection point in the browser control. When the windowClosing() method is invoked (in your dialog) you can cancel the event, display the prompt to close the window and if the user selects yes simply call EndDialog() with the desired error code:

void CMyDialog::onWindowClosing(      
    VARIANT_BOOL IsChildWindow,
    VARIANT_BOOL *Cancel)
{
    *Cancel = VARIANT_TRUE;

    UINT result = MessageBox("Close window?", "Close Window?", MB_YESNO);
    if(IDYES == result) {
        EndDialog(23);
    }
}

I am a lean mean ground beef machine!!!

Question on strict-aliasing

Hing11-Aug-09 23:40

Hing

11-Aug-09 23:40

Hi experts,

I meet a question about strict-aliasing problem when compiling a code using gcc. The problem is described below:

#include <stdio.h>
#include <stdlib.h>

unsigned long queue[10];
int queue_len = 0;

int main()
{
	unsigned long a = 0x00010002;
	unsigned short* b = (unsigned long*)(void*)&a; // we need a "(void*)" here, because we want to skip the strict-aliasing rule check.

	b[0] = 6;
	b[1] = 5;

	printf("hello world %x", (int)a); // 6 5
	return 0;
}

When you compile the code using the option below:

gcc -O3 -Wall <code file>

The result of "a" would not be changed.

However, when you compile the code using the option below:

gcc -O3 -Wall -fno-strict-aliasing <code file>

The result of "a" is changed.

This behaviour can be explained in the aliasing rule of GCC standard. The intention of strict-aliasing rule is to prevent the case that a pointee is being pointed to by a pointer of different type (the so-called type-punning error). In the case above, the pointer type of "&a" is (long*) while it is being accessed by pointer of type (short*), the action that being taken in (short*) will not take effect to the original pointee. This is a kind of trap introduced in GCC.

So, up to now, we can still explain the behavior, however, for the case below:

#include <stdio.h>
#include <stdlib.h>

typedef struct _MyStruct
{
	unsigned short a;
	unsigned short b;
}MyStruct;

typedef struct _MyStruct2
{
	unsigned char a;
	unsigned char b;
	unsigned char c;
	unsigned char d;
}MyStruct2;

int main()
{
	MyStruct a = {0x0001, 0x0002};
	MyStruct2* b = (MyStruct2*)(void*)&a;// = malloc(sizeof(unsigned short*));

	b->a = 0;
	b->b = 5;
	b->c = 0;
	b->d = 6;


	printf("hello world %x %x\r\n", (int)a.a, (int)a.b); // <-- 6 5
	return 0;
}

It should suffer from the same effect, however, the content of "a" is changed no matter you turned on the strict-aliasing rule or not.

Do anyone know what is happening in the compiler side?

You can find the open-std for C here:

http://www.open-std.org/JTC1/SC22/WG14/www/docs/n1336.pdf[^]

Take a look to section 6.3.2.3, Point 7, it states that:

A pointer to an object or incomplete type may be converted to a pointer to a different
object or incomplete type. If the resulting pointer is not correctly aligned for the
pointed-to type, the behavior is undefined.

Thanks a lot.

Re: Question on strict-aliasing

Stuart Dootson12-Aug-09 6:14

Stuart Dootson

12-Aug-09 6:14

You're misunderstanding what -fno-strict-aliasing does. GCC does strict aliasing analysis in order to optimise code, not to avoid type-punning. What it does is assume that variable references with different types can't be aliased. So, in the first case (unsigned long a; unsigned short* b;), GCC looks at the types of a and b and assumes that assignments to *b cannot affect a. So, it presumes that a is invariant across main(), so can optimise the code and inject the (presumed) constant value of a into the code generated for the printf statement. So, a never exists in memory. With -fno-strict-aliasing, you're tellng GCC it can't make that assumption, so that optimisation isn't done.

I believe the reason that -fno-strict-aliasing doesn't affect the second example is that GCC only implements the strict aliasing optimisation for variables of scalar types such as int, char, short, float etc.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Re: Question on strict-aliasing [modified]

Hing12-Aug-09 16:02

Hing

12-Aug-09 16:02

Thanks for your advice.

I do also think like that, GCC only implements the strict aliasing optimisation for variables of scalar types such as int, char, short, float etc. However, when I do an experiment below, it behaves the same as the (short*) and (long*) case (i.e. the content of the pointee is not changed):

#include <stdio.h>
#include <stdlib.h>

typedef struct _MyStruct
{
	unsigned long a;
	unsigned long b;
}MyStruct;

typedef struct _MyStruct2
{
	unsigned short a;
	unsigned short b;
}MyStruct2;

int main()
{
	MyStruct a = {0x00010002, 0x00030004};
	MyStruct2* b = (MyStruct2*)(void*)&a;// = malloc(sizeof(unsigned short*));

	b->a = 5;
	b->b = 6;

//	b[1].a = 6;


	printf("hello world %x %x\r\n", (int)a.a, (int)a.b); // <-- 6 5
	return 0;
}

Really want to know the logic behind. Do anyone know the secret?

One more example here:

#include <stdio.h>
#include <stdlib.h>

typedef struct _MyStruct
{
	unsigned char a;
	unsigned short b;
	unsigned long c;
	unsigned char d;

}MyStruct;

typedef struct _MyStruct2
{
	unsigned short a;
	unsigned char b;
}MyStruct2;

int main()
{
	MyStruct a = {0x01, 0x0002, 0x00000003, 0x04};
	MyStruct2* b = (MyStruct2*)&a;// = malloc(sizeof(unsigned short*));

	b->a = 5;
	b->b = 6;

//	b[1].a = 6;


	printf("hello world %x %x\r\n", (int)a.a, (int)a.b); // <-- 6 5
	return 0;
}

For the example above, the code will take effect (i.e. the content of the pointee is changed) no matter the strict-aliasing rule is on or off. There is even no type-puning warning apppear while compiling. Again, what is the logic behind?

BR,
Hing

modified on Thursday, August 13, 2009 2:34 AM

Examining a Message Queue

ForNow11-Aug-09 22:53

ForNow

11-Aug-09 22:53

This may be a stupid question but why is the Following code "while (PeekMessage(&msg, hwnd, 0, 0, PM_REMOVE))"

called examing the message queue in the MSDN documentation

If all I want to do is examine if a message has come in shouldn't I use PeekMessage with PM_NOREMOVE

and then if its the message I want pull the message off the queue via PeekMessage PM_REMOVE, GetMessage

or I am using Messagemaps Use the Macros to Pull off the message and go to appropriate rtn to process my message

Re: Examining a Message Queue

Stuart Dootson11-Aug-09 23:26

Stuart Dootson

11-Aug-09 23:26

I would imagine the reason they use PeekMessage with PM_REMOVE is to make it an atomic operation - why bother calling two operations (PeekMessage followed by GetMessage) when you can call one. And of course, if there's no message on the queue, the PeekMessage will return immediately anyway.

Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p

Virtual Serial Port Question

Programm3r11-Aug-09 22:24

Programm3r

11-Aug-09 22:24

Hi all,

I have found a couple of products on the web that allows me to create a virtual serial port, that was the easy part. The issue that I am facing is that the other end of the communication line is a micro-controller that isn't running any type of windows based software.

So, does anyone know of a development kit (source code) that can accommodate a communication flow from a windows software to the micro-controller? Like I said performing the steps on the windows software application should be quite simple, but it's completing the data flow on the other end.

Many thanks in advance
Kind regards,

The only programmers that are better C# programmers, are those who look like this -> Green Alien | [Alien]

Programm3r
My Blog: ^_^

Re: Virtual Serial Port Question

Cedric Moonen11-Aug-09 23:01

Cedric Moonen

11-Aug-09 23:01

I really don't see the relation with a virtual COM port Confused | :confused:

. Which kind of device are you using that creates the virtual COM port ?
Could you please elaborate a bit because I don't understand your setup.

Cédric Moonen
Software developer

Charting control [v2.0]
OpenGL game tutorial in C++

Re: Virtual Serial Port Question

Programm3r11-Aug-09 23:27

Programm3r

11-Aug-09 23:27

Sorry about that, lets try that again.

The device refers to two parts: a micro-controller and a Ethernet 2 Serial(E2S) converter. Which is connected to each other. The E2S communicates with the windows based software via the Ethernet cable. Thus I was thinking of making use of a virtual serial / Ethernet connection to communicate with the device(s). Please note that there could be more that one device / controller connected in the network.

But the thing is that the software for the E2S must be developed in such a manner to complete the communication flow between the PC software and the micro-controller. That is the tricky part. Thus I was looking for some code to get me started on this journey.

Hope that makes sense.
Kind regards,

The only programmers that are better C# programmers, are those who look like this -> Green Alien | [Alien]

Programm3r
My Blog: ^_^

Re: Virtual Serial Port Question

Randor 12-Aug-09 9:31

Randor

12-Aug-09 9:31

Programm3r wrote:
Hope that makes sense.

Not really. Your statements are extremely cryptic in my opinion and I cannot figure out what your asking. I have completed around a dozen serial to ethernet and serial to PIC microcontroller projects and have found the com0com project to be very useful. Here is the link:

Null-modem emulator[^]

Hope it helps,
-David Delaune

Re: Virtual Serial Port Question

Programm3r12-Aug-09 20:01

Programm3r

12-Aug-09 20:01

Sorry about that.
Thank you David for the info.

Kind regards,

The only programmers that are better C# programmers, are those who look like this -> Green Alien | [Alien]

Programm3r
My Blog: ^_^

how to display the IplImage into Picture control box.

DevelopmentNoob11-Aug-09 22:13

DevelopmentNoob

11-Aug-09 22:13

Hi,
I had create a 4 picture control box in my dialog. I will allow user to click on the loadImage button to load the picture, the load picture is using opencv function, cvLoadImage(). I had success to load the picture, but how can i display in that picture control box? anyone can help me?Thank you.

Re: how to display the IplImage into Picture control box.

zhu_lin11-Aug-09 22:59

zhu_lin

11-Aug-09 22:59

hi,you can use CBitmap class and there are lots of samples about showing a bitmap in the dialog, you can find it out in codeproject, and you also can get the sample from me. MSN:zhu_lin4103@126.com

I'm from China ,it's my pleasure to make friend with you. msn:zhu_lin4103@126.com

Maximum option to find a string/substring ,or compare option.

Le@rner11-Aug-09 21:01

Le@rner

11-Aug-09 21:01

Hi all,

I want to find a string from another string.

so i want to know maximum option those are used here for find string/substring or compare string.

some of them i already use.like::

1.CStringT::Compare
2.CStringT::CompareNoCase
3.StrStr Function
4.StrStrI Function
5.CStringT::Find

if some other function please tell me.

thanks in advance.

To accomplish great things, we must not only act, but also dream;
not only plan, but also believe.

Re: Maximum option to find a string/substring ,or compare option. [modified]

Adam Roderick J11-Aug-09 22:45

Adam Roderick J

11-Aug-09 22:45

u missed a couple in CString
CString::FindOneOf()
CString::ReverseFind()

Величие не Бога может быть недооценена.

modified on Wednesday, August 12, 2009 5:33 AM

Re: Maximum option to find a string/substring ,or compare option.

zhu_lin11-Aug-09 23:10

zhu_lin

11-Aug-09 23:10

some functins in the C Run-Time Library.
_mbsnBcmp
_mbsnbcmp
_mbsnbicmp
_mbsnextc,_strnextc,_wcsnextc

I'm from China ,it's my pleasure to make friend with you. msn:zhu_lin4103@126.com

load mp3 and seek by samples

javad_200511-Aug-09 20:08

javad_2005

11-Aug-09 20:08

hi i have one file of wave-Mpeg layer3 11025 16 channel 1.
mciSendstring can be load this mp3 and play it but doenst work correctly
when i get position by samples mcisendstring give me wrong. or give me wrong time .
i want to load mp3 and seek by samples and get position by samples.
do u have any way?
thanks.

Re: load mp3 and seek by samples

zhu_lin11-Aug-09 23:12

zhu_lin

11-Aug-09 23:12

hi,I used to player media file by using DirectShow SDK and work well.

I'm from China ,it's my pleasure to make friend with you. msn:zhu_lin4103@126.com

Re: load mp3 and seek by samples

javad_200512-Aug-09 1:37

javad_2005

12-Aug-09 1:37

thanks .but can be directshow sdk seek by samples.

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