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Hello,
I would like to limit access to the MS Access database that my app uses. Ideally, it would not be accessible at all from outside the app. My app will provide means to initialize and copy the database with the copy being accessible. Is there a way to do this either on the MS Access side or the VC++ side?
Thanks.
Paul Ebert
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Hi,
The good news: There is a comprehensive security setup document suite inside the help files of Access. It is relatively easy to read.
The bad news (for me): I could not get it to work reliably and usually couldn't get the options that I wanted. I gave up eventually.
My advice: download the miniSQL server version from vstudio in MSDN. It's called MSDE.
Here's a link to a Jet vs MSDE debate: http://msdn.microsoft.com/library/default.asp?URL=/library/backgrnd/html/msdeforvs.htm&RLD=462.
Here's a link to the MSDE itself: http://msdn.microsoft.com/library/default.asp?URL=/library/backgrnd/html/msdeforvs.htm
Hope this helps.
Kind regards,
Al.
VBer who wants to go back to, but will have to learn again, C++. I'll carry on using VB for the front-end; so when I get proficient at C++/STL can I jump straight to ATL and avoid the MFC?
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When is it appropriate to use the "special" data types defined in the Windows header files such as BOOL, TRUE, and FALSE, & when is it appropriate to use the standard C++ types like bool, true and false? I am programming in MFC, but I see both in code. Anyone who can help end some of this confusion would be appreciated. I understand types like CString, and COLORREF add functionality, but does it matter which one you use with the others I mentioned?
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The SDK is all C APIs, and thus must use BOOL (which is a typedef for int, I believe). They can't use bool because that is a C++ type.
MFC was developed before bool existed in C++, so it uses BOOL. New MFC features use BOOL as well, to maintain consistency.
As for when to use the built-in C++ bool, I myself don't use it much. I'm just used to using BOOL (I started doing Win programming before bool existed). I will use bool's as member variables in classes, or locals in functions. But anytime you pass a flag to an API, use BOOL, because there is no implicit conversion from bool to BOOL (ie, you can't pass a bool for a parameter declared as BOOL). If you do use bool's, you'll have to pepper your code with "bSomeFlag ? TRUE : FALSE" expressions (to explicitly convert from bool to BOOL) which is fugly.
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I do always pass directly a bool to functions expecting a BOOL, never had any problems.
Just the other direction, you must do something like this:
<br />
BOOL b_old = TRUE;<br />
bool b_new = b_old!=0;<br />
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*headscratch* I could've sworn VC complained if you used a bool where a BOOL (or other integral type) was expected. Ah well, my bad. 
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Using VC 5, the following code:
BOOL WinBool=TRUE;
bool cppBool=true;
WinBool = cppBool;
cppBool = WinBool;
produces the following:
warning C4800: 'int' : forcing value to bool 'true' or 'false' (performance warning)
I think that there are many of us C++ programers that would consider mixing types like that sloppy and we are suspicious of programmers that program like that when it is not necessary.
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My approach is to use bool everywhere remotely possible and to stay as far away from MFC as much as possible  . You never know when you might have to port your code or when MS might change their minds on BOOL.
I just use conditional returns like this if a BOOL is required:
if ( true == bState )
{
return TRUE;
}
else
{
return FALSE;
}
when I have to return a BOOL in an overridden function.
I try to never mix BOOL and bool. Even though they serve the same purpose, they are different types and should be treated as such.
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I'm having trouble using Chris's grid in a MFC extension dll. The dll is loaded into an app that isn't mine, and is supposed display a dialog when a method is invoked.
The symptoms are that if I use a custom control resource on my dialog (class=MFCGridCtrl) the dialog fails creation inside Create(). Dunno why, I just don't get a HWND. GetLastError() returns NULL. I can dynamically create the grid after the dialog is created, but then the grid never paints itself. Yes, it is WS_VISIBLE, WS_CHILD, has size, etc. Spy++ "sees" it on the dialog, but I never see it. If I float over a spot where a cell would exist, I can see a tooltip flicker in the upper left corner of the screen. The same code works in my test app, which is not using the extension dll.
I don't have any trouble with the "regular" controls on the dialog, like a CListCtrl.
My setup is pretty funky and I admit up front that the problem may not be the extension dll... One problem is that I am having to link to a non-debug MFC42.dll because the calling app is linked this way. (Although my dll does include debug info.)
Any ideas please?
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I think this problem has been already pointed out in this forum. If I remember well it was a call to AfxGetInsanceHandle() instead of AfxGetResourceHandle() somewhere in the code.
I think it has been fixed in recent updates of the control. Try with a newer version.
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Thanks for the idea. I couldn't find the article you refer to, but I did check and the source I have uses AfxGetInstanceHandle() throughout. (I'm using the source included in the sub-article Tree control and Buttons for MFC Grid control).
However, by reading the comments for Chris's article I found the reported problem with calling Initialise() from PreSubclassWindow(), and the fix. This fix enables me to successfully create the control dynamically during WM_CREATE of the dialog, but not during dialog creation from the resource template. Hmmm.
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Hi Nick,
I found the messages I referred to:
With external resourcefile dialog with Custom Control not loaded [9:24 9 Jul 00]
Anyoune knows differences with custom controls in NT and W98??? [2:00 7 Jul 00]
I don't know if the following could help, however...
A few days ago, I was trying to solve a problem I had with animated cursor resources (they got loaded only when linking to MFC DLLs, but not when linking to static libs), and I had a look in CWinApp::LoadCursor() code discovering the 'undocumented' function AfxFindResourceHandle(), which is used throughout MFC code to load resources.
Its declaration is in AFXWIN.H (line 3920):
// Use AfxFindResourceHandle to find resource in chain of extension DLLs
#ifndef _AFXDLL
#define AfxFindResourceHandle(lpszResource, lpszType) AfxGetResourceHandle()
#else
HINSTANCE AFXAPI AfxFindResourceHandle(LPCTSTR lpszName, LPCTSTR lpszType);
#endif
Here is an excerpt from MSDN ("Extension DLLs"):
"...
Sharing Resources and Classes
Exporting resources is done through a resource list. Each application contains a singly linked list of CDynLinkLibrary objects. When looking for a resource, most of the standard MFC implementations that load resources look first at the current resource module (AfxGetResourceHandle) and if the
resource is not found walk the list of CDynLinkLibrary objects attempting to load the requested resource.
Walking the list has the disadvantages that it is slightly slower and requires managing resource ID ranges. It has the advantage that a client application that links to several extension DLLs can use any DLL-provided resource without having to specify the DLL instance handle. AfxFindResourceHandle is an API used for walking the resource list to look for a given match. It takes the name and type of a resource and returns the resource handle where it was first found (or NULL).
If you wish to not walk the list and only load resources from a specific place, use the functions AfxGetResourceHandle and AfxSetResourceHandle to save the old handle and set the new handle. Be sure to restore the old resource handle before you return to the client application.
..."
---
If you have any idea about my problem, please let me know. I posted a message here, but without much luck. Hope you'll have more...
Paolo.
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I want to override CWinApp::OnFileNew and CWinApp::OnFileOpen, but I don't know how they work.
Does anybody know how they work, or even have some code for overriding them?
Thanks,
Nisse
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Just look at the MFC source code; that is what it is provided for.
As for how to override, the easiest way is to use the ClassWizard to do that.
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I was hoping so, but I can't find it!
Where can I find the MFC source code?
Thanks!
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Does anyone have an idea on how to obtain the MAC address of a PC.
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I'm in the process of building a tool that allows you to add user-defined messages and handler functions to your apps without having to manually edit files.
It seems that I need to create these messages all the time, and manually adding them to my projects (for me, that's a minimum of three files I have to change for each message) is a royal pain in the patootie.
If anyone is interested, I can put up a web page showing my progress every couple of days. The first iteration of the tool will be a stand-alone executable that can be added to your tool menu, but future plans are to make it a fully integrated add-in for Visual Studio. Of course, this too will only be applicable for Visual C++.
When the project is done, I'll post the source and executable here on The Code Project.
Comments?
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hello!
i've to change the windows opening screen in one of my applications and my own application's inteface should appear even before the desktop comes.Can you please help me?
thanks
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Hi,
CString m_sProto;
CString sProtocols="PROTOCOL";
m_sProto = sProtocols; <- This is throwing one exception.
I know it is throwing one exception catch(...).
But how to know the exception?
Thanks,
Kotesara
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Hi. This is from the MSDN.
CString::operator =
const CString& operator =( const CString& stringSrc );
throw( CMemoryException );
const CString& operator =( TCHAR ch );
throw( CMemoryException );
const CString& operator =( const unsigned char* psz );
throw( CMemoryException );
const CString& operator =( LPCWSTR lpsz );
throw( CMemoryException );
const CString& operator =( LPCSTR lpsz );
throw( CMemoryException );
Remarks
The CString assignment (=) operator reinitializes an existing CString object with new data. If the destination string (that is, the left side) is already large enough to store the new data, no new memory allocation is performed. You should be aware that memory exceptions may occur whenever you use the assignment operator because new storage is often allocated to hold the resulting CString object.
Example
The following example demonstrates the use of CString::operator =.
// example for CString::operator =
CString s1, s2; // Empty CString objects
s1 = "cat"; // s1 = "cat"
s2 = s1; // s1 and s2 each = "cat"
s1 = "the " + s1; // Or expressions
s1 = 'x'; // Or just individual characters
And heres what it says about CMemoryException.
A CMemoryException object represents an out-of-memory exception condition. No further qualification is necessary or possible. Memory exceptions are thrown automatically by new. If you write your own memory functions, using malloc, for example, then you are responsible for throwing memory exceptions.
So your catch should be something like this
try
{
// do the string stuff
}
catch(const CMemoryException e)
{
// do something with it
}
catch(...)
{
// just to catch any others that crop up.
// make sure you do somehing drastic if anything appears
// here because it SHOULD NOT HAPPEN.
}
Hope this helps. Pete
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Pete, I agree with your reply, but have a pet peeve against the catch(...) construct, especially under VC.
First, note that this code leaks:
try {
CException *e = new CException;
throw e;
}
catch(...) {
MessageBox ("Hello");
}
because the pointer is lost - there's no way to call CException->Delete(). (This leak problem is not true of all compilers, which just makes matters muddier from a portability standpoint)
Secondly, processor traps such as access voilations and divide by zero are also caught by catch(...), and there is no way that I know of to distinguish them inside the catch block.
Opinion: Catch what you expect might be thrown and can deal with, and leave the rest to the OS.
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Hi. Yes, I personally never use the catch(...) because of the very things you mention in your post. I didn't like the fact that I couldn't do anything intelligent from within the catch(...) block. If you do catch an error in catch(...) you could just tell the user and then either carry on and hope for the best or just shut down app.
Neither are optimal solutions.
If anyone has any contributions to this I would be interesting in hearing it.
Pete
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leave it to the OS? you mean the lovely "This application has performed an illegal operation" message box?
ask the average user which is more important: leaking 30 bytes or preventing the app from crashing without warning.
if i do a "catch(whatever w)", i always follow it with a catch(...). or, if i'm wrapping C code, or someone else's code, or around code that has the potential to jump out pf array bounds (like when you are filling a buffer that you didn't allocate).
in fact, i often put a catch(...) around every major code section, just in case something gets by testing. i also make sure that i do something intelligent in the catch, like attempt to get into a safe state.
the headaches that little construct can save are worth megabytes of leaked memory, to the average user.
-c
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Hi,
Try this one
catch(CException e) //i'm not sure if is pointer of not
{
TCHAR szCause[MAX_PATH];
szCause[0]=0x00;
e.GetErrorMessage(szCause,sizeof(szCause));//
}
But the best way is to read CopyConstructor help for CString because the exception types are defined there.
Best regards,
/REMUS
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