C / C++ / MFC

12-Dec-07 19:43

Hello everyone,

I am feeling template function is more tricky than template class. For the reason that the compiler will do the matching automatically for template function, but for template class, developer can assign how to match.

Sometimes compiler is doing mysterious matching rules for template function, which makes us confused. Does anyone have the same senses?

Example,

1. for template function

we define

template <class T> void sort ( vector <T>& )

when we invoke like,

sort ( vector<int> )&, T will automatically matched by compiler to int -- we have no control. Sometimes, how compiler will do the matching is mysterious.

2. for template class

developer has full control. For example, when use some template class, developer can assign the type of parameter,

we define,

template <class T> class Foo
{
    // ...
}

when developer use it, we can explicitly assign the type, like Foo <int> or Foo <bool>.

Any comments or experiences or even disagreement is welcome.

thanks in advance,
George

modified on Thursday, December 13, 2007 2:19:41 AM

Nelek12-Dec-07 21:06

Nelek

12-Dec-07 21:06

George_George wrote:
when we invoke like,

sort ( vector < int > )&, T will automatically matched by compiler to int

And.... where is the problem? You are giving a < int > what do you expect? To have a double?

I dont really understand where the problem is..

George_George wrote:
when use some template class, developer can assign the type of parameter,

And you can do a conversion of type in the first lines of the function as well, don't you?

Greetings.
--------
M.D.V. Wink | ;)

If something has a solution... Why do we have to worry about?. If it has no solution... For what reason do we have to worry about?
Help me to understand what I'm saying, and I'll explain it better to you
“The First Rule of Program Optimization: Don't do it. The Second Rule of Program Optimization (for experts only!): Don't do it yet.” - Michael A. Jackson

George_George12-Dec-07 21:47

12-Dec-07 21:47

Sorry Nelek,

I have not made myself fully understood. My question is (after reorganization),

1. for template function, we can choose to use either implicit mode to let compiler deduce or explicit mode to assign type;

2. for template class, we have to use explicit mode to assign type?

regards,
George

CPallini12-Dec-07 21:10

CPallini

12-Dec-07 21:10

IMHO:

George_George wrote:
sort ( vector<int> )&

The above doesn't make sense.

In both cases, the developer is providing explicitely the template type.

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.

George_George12-Dec-07 21:46

12-Dec-07 21:46

Sorry CPallini,

I have not made myself fully understood. My question is (after reorganization),

1. for template function, we can choose to use either implicit mode to let compiler deduce or explicit mode to assign type;

2. for template class, we have to use explicit mode to assign type?

regards,
George

Off-topic

CPallini12-Dec-07 21:54

CPallini

12-Dec-07 21:54

A curiosity:

George_George wrote:
Sorry CPallini,

I have not made myself fully understood

Do you apologize and at same time vote me down? Confused | :confused:

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.

Cedric Moonen12-Dec-07 22:03

Cedric Moonen

12-Dec-07 22:03

Yeah, that's what he call:

Any comments or experiences or even disagreement is welcome.

"You are welcome, I will just vote you down if I didn't express myself correctly and if you didn't guess what I had in mind." Unsure | :~

Cédric Moonen
Software developer

Charting control [v1.2]

CPallini12-Dec-07 22:10

CPallini

12-Dec-07 22:10

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.

George_George12-Dec-07 22:34

12-Dec-07 22:34

A bug of my mouse, CPallini!

regards,
George

George_George12-Dec-07 22:35

12-Dec-07 22:35

Sorry, CPallini!

I made a wrong click. Smile | :)

regards,
George

Cedric Moonen12-Dec-07 21:19

Cedric Moonen

12-Dec-07 21:19

I suppose that you were asking about something like this (in which case your example is very badly chosen because you specify explicitely the type):

template <class T>
void myTemplateFunc(T arg)
{
// some code here
}

And to use it, you do something like this:

int myValue = 42;
myTemplateFunc(myValue);

But, in fact even in that case there is no matching involved. The compiler will simply 'generate'a new function and replace T by an integer. Now if you call that function and supply a float, then the compiler will generate a second function and replace T by a float. You have to look at templates as code that will be generated by the compiler once you use the template (be it a class or a function). And if you call your function with two different types, then two different functions will be generated.

The only case where a matching is done, is when you use template specialization (if I provide a version of my function specifically for float for example). In that case, the compiler will try to find the best match. But in general, the compiler is quite intelligent to solve the problem on its own.

Cédric Moonen
Software developer

Charting control [v1.2]

George_George12-Dec-07 21:45

another day, another series of dumbass questions...

12-Dec-07 21:45

Thanks Cédric,

You understand my question well. My question is,

1. for template function, we can choose to use either implicit mode to let compiler deduce or explicit mode to assign type;

2. for template class, we have to use explicit mode to assign type?

regards,
George

toxcct12-Dec-07 23:16

toxcct

12-Dec-07 23:16

so,

How old are you ?

HOW OLD ARE YOU ?

HOW OLD ARE YOU ?

HOW OLD ARE YOU ?

HOW OLD ARE YOU ?

HOW OLD ARE YOU ?

HOW F***ING OLD ARE YOU ?

Sleepy | :zzz:

[VisualCalc][Binary Guide][CommDialogs] | [Forums Guidelines]

Can anyone explain me...

Nelek13-Dec-07 0:39

Nelek

13-Dec-07 0:39

[QUOTE = from the answer to my message]

Sorry Nelek,<br />
I have not made myself fully understood. My question is (after reorganization),

1. for template function, we can choose to use either implicit mode to let compiler deduce or explicit mode to assign type;
2. for template class, we have to use explicit mode to assign type?
[/QUOTE]

Ok, it has logic that if the question was not fully understood, you make the question in another way to try to get the answer you look for. But...

[QUOTE = from the answer to Cedric's message]

Thanks Cédric,<br />
You understand my question well. My question is,

1. for template function, we can choose to use either implicit mode to let compiler deduce or explicit mode to assign type;
2. for template class, we have to use explicit mode to assign type?
[/QUOTE]

If he understood you well, and you got a good answer (IMHO a perfect answer...). WHY DO YOU COPY-PASTE ANOTHER TIME THE SECOND MESSAGE?

And by the way... Why do you never answer to questions (that the people that answer your messages) make to you?

Honestly, I start thinking this user is a BOT.

Greetings.
--------
M.D.V. Wink | ;)

Re: Can anyone explain me...

George_George13-Dec-07 0:43

Re: Can anyone explain me... [modified]

13-Dec-07 0:43

Hi Nelek,

I am not a BOT. BOT is not as smart as you and me. Smile | :)

Nelek wrote:
user is a BOT

regards,
George

toxcct13-Dec-07 3:10

toxcct

13-Dec-07 3:10

George_George wrote:
BOT is not as smart as you and me.

yeah, sure you aren't. BOT is sure smarter than you Suspicious | :suss:

so, answer my previous SIMPLE question, and then i'll consider revising this statement !

[VisualCalc][Binary Guide][CommDialogs] | [Forums Guidelines]

modified on Thursday, December 13, 2007 9:19:54 AM

Help required for USB interface support for a MFC application

amit ghatwal12-Dec-07 18:57

amit ghatwal

12-Dec-07 18:57

Hi All,

This is the first time i am writing to this forum.
So let me staight come to the point .

I am a newbie to MFC , but i understand C,C++.

My urgent need of the hour is that i want to provide a text box on my GUI along with a button , and when this button is clicked the data which is shown/typed in the text box is transferred to any kind of USB device viz a viz USB Pen drive's (or any other USB 2.0 compliant class device).

So has any one done similar kind of work and if yes could you'll provide me some good links wherein i will be able to make a GUI which will allow me to talk to the USB device .
Basically the USB API 's which allows us on a click of a control button to send data to a USB device like a USB Pen drive .

Any help in this regards will be highly appreciated.

Regards
A.G

Re: Help required for USB interface support for a MFC application

Don Box12-Dec-07 19:31

Don Box

12-Dec-07 19:31

when this button is clicked the data which is shown/typed in the text box is transferred to any kind of USB device

What does it mean? A TEXT to be transferred to the USB device?

Come online at:-
jubinc@skype

Re: Help required for USB interface support for a MFC application

Cedric Moonen12-Dec-07 20:15

Cedric Moonen

12-Dec-07 20:15

A USB port is not similar to a serial port. You cannot just get a handle to the bus and send data on it. What you need to do, is get a handle to a specific device driver (using CreateFile) and then you'll be able to exchange data with this specific device (using WriteFile and ReadFile). The string you need to supply to CreateFile is something that is specific for the driver. You should check in the documentation that is supplied with the USB device (if it comes with a SDK).

Cédric Moonen
Software developer

Charting control [v1.2]

How to add SelectAll in CFileDialog

santhoshv8412-Dec-07 17:42

santhoshv84

12-Dec-07 17:42

Hi Friends,

I am using a CFileDialog, i am giving a path in that.
like..

dlg.m_ofn.lpstrInitialDir = Final_path;

Here i have to Select all the files in the CFileDialog.
How to do that?.

Thanks and Regards.
SANTHOSH V

Naveen12-Dec-07 18:16

Naveen

12-Dec-07 18:16

santhoshv84 wrote:
Here i have to Select all the files in the CFileDialog.
How to do that?.

While creating the CFileDialog object, you have to pass the OFN_ALLOWMULTISELECT also( 4th parameter )

nave

[OpenedFileFinder]

santhoshv8412-Dec-07 18:36

santhoshv84

12-Dec-07 18:36

OFN_ALLOWMULTISELECT is not my problem.

While opening the CFileDialog all the files should be selected.
How to do that?.

Thanks and Regards.
SANTHOSH V

Naveen12-Dec-07 20:51

Naveen

12-Dec-07 20:51

derive a class from the CFileDialog and overide the OnFolderChange function. Inside that function take the handle of list control and select all items in it.

nave

[OpenedFileFinder]