Re: C++ optimization problem - C / C++ / MFC Discussion Boards

Ravi Bhavnani1-Jul-04 14:10

1-Jul-04 14:10

I assume it will, since you don't have to make a function call. I also assume you're not changing the size of a_vector within the loop. Smile | :)

/ravi

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Re: C++ optimization problem

PJ Arends1-Jul-04 14:12

PJ Arends

1-Jul-04 14:12

I would use a variable.

For further reading:
http://www.codeproject.com/tips/optimizationenemy.asp[^]

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Re: C++ optimization problem

Ryan Binns1-Jul-04 14:17

Ryan Binns

1-Jul-04 14:17

Possibly, but probably not. The size() method is an inline method that simply returns the value of a member variable, so if your compiler optimises correctly it should boil down to a simple comparison with a indirect-indexed value, just the same as if it was a local variable you were comparing against. However, it's probably a good idea to store the size locally anyway, just in case the compiler doesn't optimise it for some reason, and to make it more obvious to humans that you want the code to run as fast as possible.

Obviously, if the size of the vector changes inside the loop, then you'll have to either call size() each time or update your local variable every time you do something that changes the size of the vector (add, delete etc...)

Ryan

"Punctuality is only a virtue for those who aren't smart enough to think of good excuses for being late" John Nichol "Point Of Impact"

Re: C++ optimization problem

Johan Rosengren1-Jul-04 19:44

Johan Rosengren

1-Jul-04 19:44

Why not create two small functions and test it? Remember to run in release-mode.

Re: C++ optimization problem

Antony M Kancidrowski2-Jul-04 2:11

Antony M Kancidrowski

2-Jul-04 2:11

I would compare the assembly when compiled in release mode.

Ant.

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I'm coloured, yet clear.
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Re: C++ optimization problem

Johan Rosengren2-Jul-04 2:20

Johan Rosengren

2-Jul-04 2:20

I would just time the results - if the differences were not big enough to make a mark in - say - 10 000 iterations, I wouldn't even bother optimize it Smile | :)

Re: C++ optimization problem

Antony M Kancidrowski2-Jul-04 2:35

Antony M Kancidrowski

2-Jul-04 2:35

Fair point. Most times optimization of such loops is wasted effort IMO.

Ant.

I'm hard, yet soft.
I'm coloured, yet clear.
I'm fuity and sweet.
I'm jelly, what am I? Muse on it further, I shall return! - David Williams (Little Britain)

Re: C++ optimization problem

Paul Ranson2-Jul-04 3:01

Paul Ranson

2-Jul-04 3:01

Your question implies that you are doing,

for (int ii = 0; ii < a_vector.size (); ++ii )
{
    a_vector [ ii ].DoSomething () ;
}

You may find that operator [] on vector is more expensive than size. Especially given that in many cases an interator resolves to a plain old pointer, so both the dereference and the increment are cheap.

Perhaps you could measure your way and also,

A_VECTOR::iterator it ;
A_VECTOR::iterator itE = a_vector.end () ;
for ( it = a_vector.begin () ; it != itE; ++it )
{
    (*it).DoSomething () ;
}

But it's cleanest by far to write,

class A_TYPE { ... } ;
vector<A_TYPE> a_vector ;
for_each ( a_vector.begin (), a_vector.end (), mem_fun_ref ( &A_TYPE::DoSomething )) ;

or some variant of function, functor etc that suits your code. I think this is probably potentially the fastest since the compiler has all the information to inline everything.

Paul

C++ in "Hardware structures" stand point question: Does the ALU handle any floading points operations? or will the processor let the FPU handles them?

Link26001-Jul-04 13:29

Link2600

1-Jul-04 13:29

C++ in "Hardware structures" stand point question: Does the ALU handle any floading points operations? or will the processor let the FPU handles them?
I mean, any floading point operation, both simple and complex ones.

Thanks.

Re: C++ in "Hardware structures" stand point question: Does the ALU handle any floading points operations? or will the processor let the FPU handles them?

Ryan Binns1-Jul-04 14:21

Ryan Binns

1-Jul-04 14:21

If the CPU has an FPU, then the FPU will handle all floating-point operations, as long as the compiler uses the correct instructions. If it emulates floating point in software, then the FPU will not be used. Also, if the FPU doesn't support a certain operation, it will have to be emulated in software (which, incidentally, will probably use other FPU instructions).

There are very few cases when a CPU's main ALU actually handles floating-point operations - floating-point DSP processors are the only ones I can think of.

Ryan

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Dynamic controls

richiebabes1-Jul-04 11:47

richiebabes

1-Jul-04 11:47

I have a property page that is used multiple times in a wizard with slight variations each time. Therefore for each instance of the page I want to show/not show various controls. How do I do that? I thought I could just make a control variable and then do something like m_nListBox1.SetVisible or something or other. How do I dynamically make controls visible and invisible? I am missing something obvious and it must be because I got up far too early this morning.

Re: Dynamic controls

Yawar Maajed1-Jul-04 12:22

Yawar Maajed

1-Jul-04 12:22

use CWnd::ShowWindow function to show or hide them.

Re: Dynamic controls

richiebabes1-Jul-04 12:30

richiebabes

1-Jul-04 12:30

Tried this in OnInitDialog and OnSetActive. Causes and assertion both times.

Re: Dynamic controls

Yawar Maajed1-Jul-04 13:11

Yawar Maajed

1-Jul-04 13:11

ShowWindow is THE API to use to show and hide windows, if your window does not exist yet, the function will assert.
Try making sure that the window you are calling this function on is valid before you call this function.
an exmaple of this would be
Page::OnInitDialog();
{
BOOL ret = CPropertyPage::OnInitDialog();
CWnd *pWnd = GetDlgItem(IDC_MY_WINDOW);
if (!pWnd || !::IsWindow(pWnd->GetSafeHwnd())
{
ASSERT(FALSE);
}
else
pWnd->ShowWindow(SW_HIDE); // or whatever you want to do with it.
}

Did you use classwizard to generate control variables for your window objects?
/yawar

Window title bar - detecting drag end

Anonymous1-Jul-04 11:39

Anonymous

1-Jul-04 11:39

Hi,

I have an over-ridden handler CMyDialog::OnNcLButtonDown() which detects if the user selects the title bar of my dialog. The user then drags the dialog and releases the mouse button. How can my program know when the mouse button has been released? I have tried over-riding the CMyDialog::OnNcLButtonDown() function but it does not work.

Re: Window title bar - detecting drag end

Anonymous1-Jul-04 11:41

Anonymous

1-Jul-04 11:41

Anonymous wrote:
I have tried over-riding the CMyDialog::OnNcLButtonDown() function but it does not work.

Sorry. I mean to say the CMyDialog::OnNcLButtonUp() function

Re: Window title bar - detecting drag end

Yawar Maajed1-Jul-04 12:19

Yawar Maajed

1-Jul-04 12:19

try overloading WM_NCHITTESTmessage, the code will look something like this

UINT YourClass::OnNcHitTest(CPoint point) <br />
{  <br />
  int ret = YourParentCwndBasedClass::OnNcHitTest(point);<br />
  if (ret == HTCAPTION)<br />
  {<br />
    if (GetAsyncKeyState(VK_LBUTTON) < 0)<br />
    {<br />
      if (!mbLButtonDown)<br />
      {<br />
        TRACE("\nDown");<br />
        mbLButtonDown = true;<br />
      }<br />
    }<br />
    else<br />
    {<br />
      if (mbLButtonDown)<br />
      {<br />
        TRACE("\nUp");<br />
        mbLButtonDown = false;<br />
      }<br />
    }<br />
  }<br />
  return ret;<br />
}

where mbLButtonDown would be a bool member of your class and would need to be initialized as false when constructing your window.

There might be some other way to do this too, this was just a quick thing that came to my mind.
HTH,
/yawar

Re: Window title bar - detecting drag end

Yawar Maajed1-Jul-04 12:21

Yawar Maajed

1-Jul-04 12:21

I said "try overloading".. that was not right, I meant "try writing message handler for"... Smile | :)

Re: Window title bar - detecting drag end

Ravi Bhavnani1-Jul-04 13:42

Ravi Bhavnani

1-Jul-04 13:42

Another way to detect the end of a move by dragging the caption bar is to simply handle WM_MOVE and check if the mouse is over the window's caption bar. You can do this by calling GetCursorPos() and checking if the point lies within the caption bar. GetWindowRect() and GetSystemMetrics() can help you in your computation.

/ravi

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How do you get the path to the WIndows desktop?

Terry O'Nolley1-Jul-04 11:02

Terry O'Nolley

1-Jul-04 11:02

How do you form the filepath string to indicate you want to save a file to the desktop?

I know "C:\\FOLDER\\FILE.TXT"

but what is the path to the desktop?

A client asked me to make a simple change to a downloadable web installer tool I wrote. It used to have a File...Save As dialog and they wanted me to change it to automatically save to the dektop. No problem! I said I'd do it for free. Delete the common dialog code, change the CFile.SetFilePath code from CCommonDialog.GetPathName to............ what? What is that magical cobination of ascii characters that tells my app to save to the desktop?

TIA!

//placeholder for witty verbiage

Re: How do you get the path to the WIndows desktop?

Yawar Maajed1-Jul-04 11:19

Yawar Maajed

1-Jul-04 11:19

use ::SHGetSpecialFolderLocation or SHGetSpecialFolderPath function. with folder parameter as CSIDL_COMMON_DESKTOPDIRECTORY (for all users) or as CSIDL_DESKTOP (for currently logged in user).
Functions are declared in Shlobj.h

/yawar

Re: How do you get the path to the WIndows desktop?

Terry O'Nolley1-Jul-04 12:07

Terry O'Nolley

1-Jul-04 12:07

Fantastic Yawar!

I googled, I searched but I never would have thought to look there Smile | :)

This did the trick. Thanks.

//placeholder for witty verbiage

Re: How do you get the path to the WIndows desktop?

palbano1-Jul-04 11:20

palbano

1-Jul-04 11:20

SHGetSpecialFolderLocation()

"No matter where you go, there your are." - Buckaroo Banzai

-pete

How to write a program to auto-fill an HTML page?

Anonymous1-Jul-04 10:42

Anonymous

1-Jul-04 10:42

Hi,
I am quite new to Internet Programming.
I am trying to create a program that will load an HTML page from an address i give to him, and fill the edit boxes with values i have in memory (let's say... any constants for now)..

For example, the interface should have just a text box to enter the URL, a fill button, and an area for HTML page to appear in.

When i enter the URL and press enter, the HTML area loads the page with the URL (PROBLEM #1.. dunno how to do this!)

When i press Fill, the text areas get filled by some constant (PROBLEM #2.. dunno how to do this!)

Could you please help? Is there any kind of documentations that will be of help?

Thank you very much for all the help in advance.. Rose | [Rose]

Re: How to write a program to auto-fill an HTML page?

Anders Molin1-Jul-04 13:51

Anders Molin

1-Jul-04 13:51

Anonymous wrote:
When i enter the URL and press enter, the HTML area loads the page with the URL (PROBLEM #1.. dunno how to do this!)

http://realdevs.net/Default.aspx?tabid=83[^]

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