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Few years ago we ported our application low-level to MFC. Instead of using open, read, write etc. we moved to MFC specifics like CreateFile(), ReadFile & WriteFile. We also did the same for the locking functions i.e. use LockFileEx instead of fcntl. Recently we start using WRITE_THROUGH flags everywhere to force direct writing to disk rather than via O.S system cache. Whilst most customers are happy and solved few of their problems some of them still have issues that are hard to track and reproduce. Hence there is a thought to go back to POSIX I/O API but this may creates us again more problems than it solves.
My question is the following: Assuming that we are targeting a Win32 platform (XP and Vista) which I/O is the better low-level I/O it terms of a) performance, b) security of the following choices?
i. MFC specific functions like CreateFile, LockFileEx etc.
ii. POSIX style low-level I/O API like _open(), _fcntl()using a VC++ compiler
iii. POSIX style low-level I/O but this time using a late version gcc/g++ compiler.
If someone has the same dillemas would be nice to hear the views. Also if someone knows any article or comparisons could you please direct me to them?
Thanks.
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If you're targetting only Windows then I would (politely) suggest you Win32 API, such as CreateFile, LockFileEx, etc..
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]
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Short answer
If your only targeting Windows platforms use CreateFile.
Longer answer
The main reason you would want to use the CRT functions (open() close() etc) is to make your program more portable there isn't any obvious advantage in speed or performance.
That said, using win32 APIs does allows you to specify various parameters that CRT doesn't like Security attributes, Template file etc.
It doesn't really matter what compiler you use in terms of the APIs you call the CRT you will use is the same regardless of the compiler used. That said I don't see a reason to use gcc to compile code for Windows.
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I am aware of the portability benefits of CRT functions. I also know that in standard C their API derives from the UNIX system calls. To my knowledge in a UNIX system usually (if not always) there isn't a lower level I/O function than open, read etc.
However, I couldn't find what happens in Win32 platforms. Are the CreateFile, ReadFile the equivalent of system calls? Does this mean that CRT functions like open or read are implemented using CreateFile and ReadFile. I suspect this is the case but I couldn't find any MS documentation stating that. It would be interesting actually to see outline of implementation of open/read etc using Win32 API and see what flags do they pass etc. if of course that's the way they have been written.
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Dimitris Vikeloudas wrote: Does this mean that CRT functions like open or read are implemented using CreateFile and ReadFile.
Yes. On the Windows platform many of the CRT functions are nothing more than wrappers for their Windows API equivalents. The function in question... fopen will ultimately result in a call to the CreateFile Function[^] with the OPEN_EXISTING disposition. Which is yet another wrapper for CreateFileW if your in a non-unicode build. Calling CreateFileW with OPEN_EXISTING will result in a call to the NtOpenFile Function[^] which will push all the arguments on the stack and will pass through a call gate[^] via the SYSENTER instruction and result in a call to the ZwOpenFile[^] function.
Best Wishes,
-David Delaune
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Thanks a lot...That clarifies a lot the picture.
I can suspect that compilers like g++ may provide their own implementation of open & read using the NtOpenFile or ZwOpenFile but from my perspective these internal functions are a no-go area. CreateFile etc are low-level enough
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Hi all,
I am new to VC++..
I saw that "void SetOwner(CWnd* pOwnerWnd)" is windows defined function..
Can we overwrite this function to our needs??
is there any function that do the same purpose, done by setowner function??
Thanks,
Rakesh.
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CWnd::SetOwner is a method of the MFC CWnd class. Since it isn't virtual you cannot override it (BTW: what would be the purpose of doing it?).
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]
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HI all
i m using FindItem find string in ListCtrl but its not find Exact string please tell me how can i find exact string with FindItem.
i m using this code.
CListCtrl m_list;
LVFINDINFO info;
int nIndex;
info.flags = LVFI_PARTIAL|LVFI_STRING;
info.psz = _T("Test");
while ((nIndex = m_list.FindItem(&info)) != -1)
{
m_list.DeleteItem(nIndex);
}
here it can delete "test","test1" etc.
please help me for this.
To accomplish great things, we must not only act, but also dream;
not only plan, but also believe.
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Perhaps the find is case sensitive. You specified
_T("Test")but the strings you show begin with
"test" (notice the first letter case difference).
Hope that helps.
Karl - WK5M
PP-ASEL-IA (N43CS)
PGP Key: 0xDB02E193
PGP Key Fingerprint: 8F06 5A2E 2735 892B 821C 871A 0411 94EA DB02 E193
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First look for some overload of Find method that takes some argument to tell him that this find is case sensitive.
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How to select correct width to lock from 24bpp bitmap of random width, that the locked bitmpa data has the stride equal to 3 * locked bitmap data width?
bitmapData.stride == bitmapData.width * 3
Чесноков
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Depends how your bitmap is stored.
If you have this structure:
BITMAPINFOHEADER bmHeader it has a member
LONG width = bmHeader.biWidth
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I need to do it using GDI+
How do we need to decrease bitmap width, that after it was locked to read its RGB triplets, the stride in that array will be equal to (3 * width)
e.g. 640x480 24bpp bitmap has stride 1920 = 3 * 640
but some 257x150 24bpp has stride not equal to 3 * 257
What is the formula to decrease 257 to fit into 3 * width = stride?
Чесноков
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I believe the memory holding the pixel data is DWORD aligned. So wouldnt you just do:
#define ALIGN(val)((val + 3) & ~3)
DWORD iSize = (sizeof(RGBTRIPLE) * bitmapData.width);
iSize = ALIGN(iSize);
Am I right?
Best Wishes,
-David Delaune
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say we have width = 257;
what is the width should be to (width * 3) % 4 = 0
Чесноков
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(((257 * sizeof(RGBTRIPLE)) + 3) & ~3) == 772;
Best Wishes,
-David Delaune
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I do not need to estimate stride of bitmap given the width I need to estimate width of the bitmap for a stride. In the equation 257 is the x variable needed to be found:
(((x * sizeof(RGBTRIPLE))) + 3) & ~3) = 772
we have width = 257
257 * 3 = 771, 771 / sizeof(DWORD) = 192.75
hence we need to decrease 257 the way the stride / 4 = integer
252 * 3 = 756, 756 / sizeof(DWORD) = 189
How can we found that width = 252 from original 257?
Чесноков
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I am not understanding the numbers you are showing me. For example:
Chesnokov Yuriy wrote: 257 * 3 = 771, 771 / sizeof(DWORD) = 192.75
Why are you dividing 771 by sizeof(DWORD)? This does not make any sense to me. Each pixel is represented by 3 bytes or sizeof(RGBTRIPLE). The padding will be at the end of the memory allocated. Like this:
xxxxxxxxxxxxxxxxPADDING
You should be able to calculate the original bitmap width by checking that stride modulo RGBTRIPLE is equal to zero. For finding the best width where width is equal to stride you can multiply width by RGBTRIPLE and check that it is equal to the alignment. Something like this:
#define ALIGN(val)((val + 3) & ~3)
#define ISSTRIDEALIGNED(val)((val * sizeof(RGBTRIPLE)) == ALIGN(val * sizeof(RGBTRIPLE)))
DWORD OriginalWidth24(DWORD dwInStride)
{
if(0 != dwInStride % sizeof(RGBTRIPLE))
{
--dwInStride;
}
return dwInStride / sizeof(RGBTRIPLE);
}
DWORD BestWidthEqualStride(DWORD dwWidth)
{
while(dwWidth && (sizeof(RGBTRIPLE) * dwWidth) != ALIGN(dwWidth * sizeof(RGBTRIPLE)))
{
--dwWidth;
}
return dwWidth;
}
And you can check their values:
DWORD dwBitmapWidth = 257;
DWORD dwNonAlignedSize = (dwBitmapWidth * sizeof(RGBTRIPLE));
DWORD dwAlignedSize = ALIGN(dwBitmapWidth * sizeof(RGBTRIPLE));
DWORD dwOriginalWidth = OriginalWidth24(dwAlignedSize);
DWORD dwWidthEqualsStride = BestWidthEqualStride(dwBitmapWidth);
Best Wishes,
-David Delaune
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Hi techies,
I have a problem and i really dont know how this happens.
I have a property page window with say 4 property pages.(sheet1,sheet2,sheet3sheet4) and obviously they all have common "Ok" "Apply" and "Cancel" button. Each of the sheets have their own classes say Csheet1,Csheet2,Csheet3,Csheet4 with each of them having their own function definations for "Ok" "Apply" and "Cancel" (like Csheet1:: onOK(), Csheet2:: onOK(), Csheet4:: onOK(),, etc).
But if im in sheet4 and press Ok or Apply why the hell it goes to Csheet1:: onOK() and then to Csheet4:: onOK(),, though im averse to this action. please help me...!!
i just want the functions of class correponding to the sheets to be invoked.
say if im in sheet1 and press "ok" or "Apply" then Csheet1:: onOK() or Csheet1:: onApply() resp. should be opened..!!1
please get a solution.
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Does the problem only happen on the sheet4 when you click the 'ok' button and it jumps to the Csheet1::onOK() function?
aravind.sn wrote: ... and obviously they all have common "Ok" "Apply" and "Cancel" button.
Also from the above, are you saying that they all share the same buttons ? if that is so then that is the problem !
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Yes any page you go and click ok, it will first go to the Csheet1::onOK() and then to their class defined Csheetx::onOK() funtion.
"Also from the above, are you saying that they all share the same buttons ? if that is so then that is the problem !"
RE: Generally its the property of the property page which looks like sharing the same "OK" "Apply" and "Cancel" button,, for example,, open your Internet option (in internet explorer) the bottom 3 buttons look like common.
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hi
Where does the ACL of any file or directory is stored ?
say if we created an acl for a file in windows operating system
and moved that file to another operating system like mac
does that previously created ACL still holds to that file ??
Thanks
Anil Veeraghattapu
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I have a MFC SDI project(use multiple byte) created in VC++ 2003. Now I convert it to VC+2008.
I add the SetTitle("aaa.bbb") in OpenFile function, but the title does not change.
I create a new MFC SDI project and SetTitle("aaa.bbb") in openFile function, and then the title change to be "aaa.bbb".
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