Re: why it prints 3? - C / C++ / MFC Discussion Boards

Re: CreateWindowEx causes application crash.

Cedric Moonen15-Jul-09 20:27

15-Jul-09 20:27

Could you tell us the exact error message ? Where does it crash exactly ? Try to use your debugger to collect more information.

Cédric Moonen
Software developer

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

Read a files summary

OrCs23615-Jul-09 14:19

OrCs236

15-Jul-09 14:19

I can't figure out how to read a files summary (Title, Subject, Author, Category, Keywords, Comments, etc.. The tab under properties).

If anyone could show me how to do this you would make my day Smile | :)

Re: Read a files summary

Randor 15-Jul-09 14:58

Randor

15-Jul-09 14:58

You can access that information through the IPropertyStorage[^] and IPropertySetStorage[^] interfaces.

How To Read Compound Document Properties Directly with VC++[^]

Best Wishes,
-David Delaune

why it prints 3?

sam_psycho15-Jul-09 10:01

sam_psycho

15-Jul-09 10:01

Can anybody tell me why value of b is 3 in this code? what happens with (a=0) exactly?

int a=0;
int b=(a=0)?2:3;
cout<<b;

Re: why it prints 3?

David Crow15-Jul-09 10:08

David Crow

15-Jul-09 10:08

Because the statement within parenthesis, which assigns 0 to a, equates to 0 (false), thus assigning 3 to b. If you change it to:

int b = (a = 1) ? 2 : 3;

it might make more sense.

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

Re: why it prints 3?

CPallini15-Jul-09 10:16

CPallini

15-Jul-09 10:16

DavidCrow wrote:
change it to:

int b = (a = 1) ? 2 : 3;

it might make more sense.

Does it really make more sense?
Smile | :)

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: why it prints 3?

David Crow15-Jul-09 10:17

David Crow

15-Jul-09 10:17

In that it would instead assign 2 to b, yes.

Re: why it prints 3?

CPallini15-Jul-09 10:20

CPallini

15-Jul-09 10:20

Ah, OK, it makes a lot more sense... Big Grin | :-D

Re: why it prints 3?

CPallini15-Jul-09 10:13

CPallini

15-Jul-09 10:13

The result of the expression (assignment)

(a=0)

is 0, i.e. the value of a (that is false for the conditional operator ?).
hence the result of the expression

VCD_A wrote:
(a=0)?2:3

is 3.

Re: why it prints 3?

Stuart Dootson15-Jul-09 12:24

Stuart Dootson

15-Jul-09 12:24

a=0 is assignment. You probably wanted a==0 (two = signs), which is hte equality test.

One of the things that's nice (when you're experienced), yet horrible (when you're learning) about C and C++ is that assignment is an expression, not a statement, which means that you can do what you've done there.

In other languages like Ada, which class assignment as a statement, you couldn't make that mistake.

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

Re: why it prints 3?

sam_psycho15-Jul-09 15:25

sam_psycho

15-Jul-09 15:25

but if your are assigning any thing to any variable(in our case a=0), this statement suppose to a true, and a=1 does, but what is wrong with zero?

Re: why it prints 3?

«_Superman_»15-Jul-09 17:03

«_Superman_»

15-Jul-09 17:03

In C (and C++) 0 equates to false and non-zero equates to true.

The case that you mentioned is similar to

int a = 0;
if (a)
{
   b = 2;
}
else
{
   b = 3;
}

Since a is 0, this equates to if(0) or if(false).
So the else part will be executed.

But in the following snippet, the if part will be executed.

int a = -1;
if (a)
{
   b = 2;
}
else
{
   b = 3;
}

«_Superman_»
I love work. It gives me something to do between weekends.

Re: why it prints 3?

harold aptroot15-Jul-09 18:43

harold aptroot

15-Jul-09 18:43

The result of assignment is the value that was assigned to the lvalue, not some sort of status flag indicating that the assignment succeeded. The result of a=x is x, thus a=0 equals 0.

Re: why it prints 3?

David Crow16-Jul-09 2:59

David Crow

16-Jul-09 2:59

VCD_A wrote:
but if your are assigning any thing to any variable(in our case a=0), this statement suppose to a true...

So what would you propose the value of a and b to be in the following:

int a, b, c;
a = b = c = 5;

Hint: it's not 1.

PaintDesktop

daavena15-Jul-09 9:45

daavena

15-Jul-09 9:45

Hello,

I want to obtain desktop background, so I would like to use PaintDesktop(hdc) function;

SDK says:
The PaintDesktop function fills the clipping region in the specified device context with the desktop pattern or wallpaper

HRGN hReg = CreateRectRgn(0,0,10,10);
HDC hdcD = GetWindowDC(GetDesktopWindow());
hdc = CreateCompatibleDC(hdcD);
SelectObject(hdc,hReg);

bResult = PaintDesktop(hdc);

But PaintDesktop function always returns false.

What am I doning wrong? Could you give me a hint.

Thank you.

Re: PaintDesktop

CPallini15-Jul-09 10:19

CPallini

15-Jul-09 10:19

Why don't you call GetLastError on PaintDesktop failure?
Smile | :)

Re: PaintDesktop

Sauce!21-Jul-09 6:19

Sauce!

21-Jul-09 6:19

or if you're lazy, add @err,hr to your watch window Smile | :)

Bufferring PAckets

resolvequestion15-Jul-09 9:11

resolvequestion

15-Jul-09 9:11

Can anyone help me with example code where u can use (vector, queue, dequeue , map techniques)

Thanks Stuart Dootson &; Superman !

I will be receiving certain amount of packets but I am not sure exactly how much. There will no memory problem as certainly its being taken under consideration that the received packets will be at certain limit it will not exceed.

whats the difference between using vector versus dequeue or queue technique.

I am explaining my scenario . I have reader thread that will do blocking read and once it receives the first packet which will be of 20W with 1W header with it.. I need to calculate checksum of the 20W packet received. Than I need to read certain fields and need to decide where it needs to be buffered. Before buffering these packets I need to strip off the 1W header. Once the buffering is complete say I might receieve 500 packets of size 20Word. After I stop receving the packets. I need to analyze the packets that being buffered. And these packets are of 2 types theere might be 2W packet and 260W packet or partial packet and each of these packet will have header so. first I need to read the packet header of the first received packet inthe buffer and base don that I need to dispatch those packets to its destined location or hand over to the designated handler.

So confusion is whats the best efficient technique I should use. Using simple array is not best option so thought of asking here. Also how do Istrip off the header from the packet.

Any help woul dbe appreciated. I have just started coding but have not really much coded in C++ .. I am learning by dng google or reading previos discussion here on forum

THANKS!!!!

Re: Bufferring PAckets

Randor 15-Jul-09 11:31

Randor

15-Jul-09 11:31

You should probably use deque. In my opinion it would be best suited for your application requirments. A Microsoft sample of deque:

INFO: STL Sample for deque::push_back and deque::pop_back Functions[^]

A in-depth deque analysis by a codeproject member:

An In-Depth Study of the STL Deque Container[^]

resolvequestion wrote:
whats the difference between using vector versus dequeue or queue technique

This is not really the type of information that is obtained through a forum. You should probably invest a few hours and research the difference between the STL containers. Here is a good place to start:

STL Container Comparison[^]

STL Containers[^]

resolvequestion wrote:
Also how do I strip off the header from the packet.

//I believe you state that the header is the size of 1 WORD
WORD packet_buffer[20]; //The first element of the array is indexed of 0
WORD packet_head = packet_buffer[0]; //Assign packet_header the value of WORD at index zero
WORD *piStripped = &packet_buffer[1]; //Pointer to WORD at index 1 of zero based WORD array.
BYTE *pbStripped = (BYTE *)&packet_buffer[1]; //Pointer to BYTE at index 1 of zero based WORD array.

resolvequestion wrote:
Any help woul dbe appreciated. I have just started coding but have not really much coded in C+

Excellent, in my opinion codeproject is the best programming resource on the internet.

Good luck,
-David Delaune

Re: Bufferring PAckets

«_Superman_»15-Jul-09 17:15

«_Superman_»

15-Jul-09 17:15

resolvequestion wrote:
whats the difference between using vector versus dequeue or queue technique

Each of the STL containers are optimized for certain types of operations.
Read more about it here - STL Containers[^]

For example, vector is optimized for random access to any of its elements.
A deque is optimized for insertions and removal of elements at both its ends.

As suggested by Stuart in your earlier post, a deque will be perfect for your needs.

«_Superman_»
I love work. It gives me something to do between weekends.

wavelet transform c++ program

mrby12315-Jul-09 8:34

mrby123

15-Jul-09 8:34

Dear friends,

I am looking for C++ programs of wavelet transform for seismic waves. Although, I can do wavelet transform with Matcad, I like to get an independent program.

Thanks

Yours

Re: wavelet transform c++ program

CPallini15-Jul-09 9:34

CPallini

15-Jul-09 9:34