function templates - C++ standard vs. VC6 - C / C++ / MFC Discussion Boards

Re: WaitForMultipleObjects()..

gokings3-Aug-04 20:50

gokings

3-Aug-04 20:50

Would it be possible to have multiple threads waiting? Each thread would wait for no more than 64 events.

Re: WaitForMultipleObjects()..

Laing,James3-Aug-04 22:22

Laing,James

3-Aug-04 22:22

Thank you for the reply.

I had thought of that, but again I did not want to compromise the throughput speed that the application currently delivers.

But, I have been thinking about this all night and I cannot think of another solution that would 'scale' as well as your suggestion.

So, it looks like thats the road I will have to take.

Best regards.
And again, thank you for the reply.

James.

Re: WaitForMultipleObjects()..

Laing,James4-Aug-04 7:23

Laing,James

4-Aug-04 7:23

After much deliberation and study of my code, I have decided to abandon the idea of trying to handle more than 64 events.
It is just not possible to integrate multiple threads, each waiting on a set of 64 events.

I need to be able to maintain the current application throughput and the overhead would be too much.
The list of events that I wait on is not constant and is waited on upto 3000 times per second.

The intended user will just have to deal with the limitation.

So thats that.

How Many Timers can run on a dialog

Member 12742903-Aug-04 9:00

Member 1274290

3-Aug-04 9:00

Hi,

I have a question if there is a limitation on the number of timers that could run on a Dialog.

SetTimer method of the CWnd class is used.

Re: How Many Timers can run on a dialog

T1TAN3-Aug-04 11:05

T1TAN

3-Aug-04 11:05

Hi,

AFAIK (As Far As I Know) there is only a limitation within Windoze, they say there is a maximum of timer handles Windoze can handle (how poetic), but I've never heard of a limit within a dialog..? D'Oh! | :doh:

hope it helps... Cool | :cool:

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Re: How Many Timers can run on a dialog

Member 12742903-Aug-04 11:33

Member 1274290

3-Aug-04 11:33

ok let me reframe the question to how many timer handles Windoze can handle given the fact that all the "OnTimer" processing happens on a single UI thread

Re: How Many Timers can run on a dialog

Michael Dunn3-Aug-04 13:13

Michael Dunn

3-Aug-04 13:13

Since the timer ID is a non-zero UINT, that places a theoretical limit of 4294967294 timers per window. However the internal data required by a timer would fill up the 2GB address space before you reach that limit.

--Mike--
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function templates - C++ standard vs. VC6

peterchen3-Aug-04 8:54

peterchen

3-Aug-04 8:54

I see the following behavior under VC6:

template <class T> void foo()
{
   printf("sizeof(..)=%i\n", sizeof(T));
}


int main(int argc, char * argv[])
{
   foo<BYTE>();  // (*) prints 4 !!!!
   foo<float>(); // prints 4
   return 0;
}

(the real implementation is a bit more complex, it's a bit more complex, seems like at (*) VC6 chooses to call the float variant)

However, when I change the function declaration to

template <class T> void foo(T * p = NULL)
{
   printf("sizeof(..)=%i\n", sizeof(T));
}

it seems to work correctly.

I know that you can't templatize functions by values, only by types - btu that the types must appear in the argument list??!!

Is this (yet another template-related) bug of VC6, or is this what the C++ Standard says?

(I'm pretty much pissed anyway, checking a few dozen templates if they need the T*=NULL trick, but I'd like to know at least if it's my ignorance or the compiler's fault)

we are here to help each other get through this thing, whatever it is Vonnegut jr.

sighist || Agile Programming | doxygen

Re: function templates - C++ standard vs. VC6

C^hris L^osinger3-Aug-04 10:14

C^hris L^osinger

3-Aug-04 10:14

must be a VC6 bug. the same code in VC7 gives the correct result.

Software | Cleek

Re: function templates - C++ standard vs. VC6

Michael Dunn3-Aug-04 13:16

Michael Dunn

3-Aug-04 13:16

Yes, VC 6 has problems when a type template parameter doesn't appear in the function's parameter list. Your dummy T* p = NULL parameter is the normal workaround. Wink | ;)

--Mike--
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Re: function templates - C++ standard vs. VC6

peterchen3-Aug-04 20:05

peterchen

3-Aug-04 20:05

does this mean I'm "normal"? Roll eyes | :rolleyes:

we are here to help each other get through this thing, whatever it is Vonnegut jr.

sighist || Agile Programming | doxygen

Calling classes from DLLs

Bisyork3-Aug-04 8:20

Bisyork

3-Aug-04 8:20

I have been having problems trying to set up a plugin for my program. The program loads a DLL dynamically, and then calls a member function:

__declspec(dllexport) int Start(CDervDlg *dlg)
{
	dlg->m_SomeVar = TRUE; //Works fine
	dlg->SomeFunc("Blah", "Blah"); //Link error: unresolved external symbol.
}

I've tried using both regular DLLs and Extension DLLs, but neither work.
This is probably just something obvious that I just can't see, but can anyone help?

Re: Calling classes from DLLs

Jaime Stuardo3-Aug-04 9:01

Jaime Stuardo

3-Aug-04 9:01

if SomeFunc is on the DLL, you have to dllexport it when generating the DLL and dllimport when generating the EXE.

If it is an MFC extension DLL, you can use the AFX_EXT_CLASS macro, for example:

class AFX_EXT_CLASS CMyDlg : public CDialog
{

};

Jaime

Re: Calling classes from DLLs

Bisyork3-Aug-04 10:50

Bisyork

3-Aug-04 10:50

Somefunc is in the EXE.

///EXE code
class CDervDlg : public CDialog
{
	void TestLoad();
	void SomeFunc(CString, CString);

	BOOL m_SomeVar;
};


typedef int (*SCGptr)(CDervDlg *);
void TestLoad()
{
	HINSTANCE inst = AfxLoadLibrary("testlib.dll");		
	SCGptr Startfunc = (SCGptr)GetProcAddress(inst, "?Start@@YAHPAVCDervDlg@@@Z");
	if (Startfunc != NULL)
		Startfunc(this);
}


///DLL code
#include "DervDlg.h"

__declspec(dllexport) int Start(CDervDlg *dlg)
{
	dlg->m_SomeVar = TRUE; //Works fine	
	dlg->SomeFunc("Blah", "Blah"); //Link error: unresolved external symbol.
}

Thank you for helping.

Re: Calling classes from DLLs

Jaime Stuardo3-Aug-04 11:03

Jaime Stuardo

3-Aug-04 11:03

In DLL you have to declare:
class __declspect(dllimport) CDervDlg : public CDialog
{
void TestLoad();
void SomeFunc(CString, CString);

BOOL m_SomeVar;
};

and in EXE:
class __declspect(dllexport) CDervDlg : public CDialog
{
void TestLoad();
void SomeFunc(CString, CString);

BOOL m_SomeVar;
};

In your DLL you are using a function declared in the EXE, that's why you need to export from the EXE, and import it into the DLL.

Jaime

Re: Calling classes from DLLs

Bisyork3-Aug-04 14:52

Bisyork

3-Aug-04 14:52

Thank you very much. It works now.

CDatabase && CRecordSet

0v3rloader3-Aug-04 6:38

0v3rloader

3-Aug-04 6:38

Hello,

In terms of performance, good programming, etc, is it better to derive [customized] classes from CDatabase and CRecordSet or is it preferable to build our own from scratch? What do you think about this?

What I am trying to know is whether a Database Programmer finds all the functionalities he/she needs in these MFC classes or whether they'd be better off creating their own from scratch.

All insights on the subject are very much appreciated. Smile | :)

Thank you,

David

Re: CDatabase && CRecordSet

Jaime Stuardo3-Aug-04 9:18

Jaime Stuardo

3-Aug-04 9:18

AFAIK CDatabase, CRectordset, etc, connects to a database by using ODBC driver, and that way of connection is always slower than accessing directly database native driver, as it adds other layer to the database connection. They are easy to use, bad provide poor performance.

To connect to database I programmed my own class named CDatabase that encapsulates all database connection using ADO.

It's known that by using ADO, the program doesn't access directly the database driver, but it's only one layer over the OLEDB driver, being a good choice (and easy choice) to access a database.

Jaime

But...

0v3rloader3-Aug-04 10:06

0v3rloader

3-Aug-04 10:06

But what kind of database(s) do you usually use? MsAccess and the likes, or Oracle/... ?
I am asking this because I heard something before about the ADO technology only allowing you to connect to the Microsoft Jet-type databases. Is this right?

dNimrod#X
________________________

Re: But...

Jaime Stuardo3-Aug-04 10:15

Jaime Stuardo

3-Aug-04 10:15

it's wrong. ADO can connect to any database that has supporting driver installed in the system. I have used it in Access (Microsoft Jet), SQL Server (SQLOLEDB) and Oracle (MSDAORA)

Jaime

Great!

0v3rloader3-Aug-04 10:31

0v3rloader

3-Aug-04 10:31

I see! I hope you'll bear with me, I am a newbee in database programming... WTF | :WTF:

Let me ask you though, is there any MFC class supporting ADODB connections?, I've been searching but found none...

For what I could see, ADODB connections are a form of interacting with databases through OLE ?

Re: Great!

Jaime Stuardo3-Aug-04 10:56

Jaime Stuardo

3-Aug-04 10:56

MFC doesn't provide a class for connecting to database using ADODB, that's why I programmed my own CDatabase class that #imports the ADO DLL to use the wrapper classes, and call the more common methods, for example, Execute to execute a query.

In order to fully understand, you need knowledge on COM technology.

I think here in codeproject you may be able to find info on this topic (in www.google.cl you can find a lot of stuff, for sure)

Jaime

Thanks

0v3rloader3-Aug-04 11:41

0v3rloader

3-Aug-04 11:41

Thanks a lot for all the input, Eduardo!

Cheers,

David

Re: Thanks

Jaime Stuardo3-Aug-04 14:20

Jaime Stuardo

3-Aug-04 14:20

you are welcome... but my name isn't Eduardo, it is Jaime, and my surname Stuardo Smile | :)

Re: Thanks

0v3rloader3-Aug-04 23:09

0v3rloader

3-Aug-04 23:09

I am sorry for having mixed up your name, Jaime!

Again, thanks for the help!
Smile | :)

David

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