C / C++ / MFC

Aidman7-Jan-03 3:28

Aidman

7-Jan-03 3:28

Any ideas of where I could find some info on this type function pointer calls?

Stefan Pedersen7-Jan-03 3:34

Stefan Pedersen

7-Jan-03 3:34

You might want to check out
http://www.codeproject.com/cpp/calling_conventions_demystified.asp[^]

"You can stand all night at a redlight anywhere in town, hailing Marys left and right but none of them slow down. I've seen the best of men go past. I don't wanna be the last..."

Todd Smith7-Jan-03 5:46

Todd Smith

7-Jan-03 5:46

It looks you're trying to create a scripting engine. If that's the case then most scripting engines accept arguments as strings and then convert those arguments into the proper types.

int TheRealFunc(const char* argument)
{
    // agument is an integer so lets convert
    int i = atoi(argument);

    // blah blah blah
}

Or, for each "real" function there's a wrapper function for your scripting engine that parses the parameters and then does the real call

int TheRealFunc(int a1, int a2, float a3)
{
    // blah blah blah
}

int TheRealFuncWrapper(const char* argument1, const char* argument2, const char* argument3)
{
    // convert the parameters
    int a1 = atoi(argument1);
    int a2 = atoi(argument2);
    float a3 = atof(argument3);

    return TheRealFunc(a1, a2, a3);
}

Todd Smith

Aidman7-Jan-03 6:37

Aidman

7-Jan-03 6:37

You guessed right, I am trying to create a simple script that can call function in the application that runs the script. But my "script engine", if you real can call it that, is declared as a class where you should be able to call a function named "AddFunction" and you simple add the pointer of the function you want to add into the script class so the script can call it. And also the script has to be able to call win32 API dll calls. Please help how can I make this work, how do I make the call and get the a pointer of the function I wanto add? Confused | :confused:

Aidman » over and out

Chris Richardson7-Jan-03 7:38

Chris Richardson

7-Jan-03 7:38

If you are looking to create a scripting engine, take a look at the IDispatch interface in the MSDN. Specifically, the Invoke member of IDispatch. What it defines is sort of what you are looking for I think.

Chris Richardson

Programmers find all sorts of ingenious ways to screw ourselves over. - Tim Smith

Aidman7-Jan-03 10:50

Aidman

7-Jan-03 10:50

Please understand that I don't wanto use any already designed scripts, escially an script object. I wanto create my own language and own engine Smile | :)

Aidman » over and out

Function Pointers in OOP

tilli again6-Jan-03 11:11

tilli again

6-Jan-03 11:11

Hey everyone!

Okay, I have the following code:

typedef int (*funcP) (int v1, int v2);

struct pStruc
{
funcP callback;
};

struct pStruc *callbacks;

int someFunc (int v1, int v2)
{
return v1 + v2;
}

int anotherFunc (int v1, int v2)
{
return v1 - v2;
}

struct pStruc *assignFuncs ()
{
return (struct pStruc []) {&someFunc, &anotherFunc};
}

void main ()
{
callbacks = assignFuncs ();
cout << callbacks->callback (10, 20);
}

Output will be 30.

You should get the idea: I have an array of function pointers, and I need to call the stored functions. Works so far. Now, what will I have to do if assignFuncs as well as the two refered functions are members of some class? I'd like to have it working in a very flexible way, without any hardcoded class name! Any idea?

tilli

Alvaro Mendez6-Jan-03 11:38

Alvaro Mendez

6-Jan-03 11:38

I'd like to give you an exact answer but I'm afraid my experience with member function pointers is extremely limited (thank God). If you haven't already, you may want to search the C/C++ articles here for ways of accomplishing what you need.

What I'd like to know is why? Why go through this syntactic nightmare when OO techniques such as virtual functions may provide a more elegant and maintainable solution?

Regards,
Alvaro

Well done is better than well said. -- Benjamin Franklin
(I actually prefer medium-well.)

William E. Kempf6-Jan-03 12:03

William E. Kempf

6-Jan-03 12:03

C++ is strongly typed, so you can't use member-function pointers with out a class name. Nor can you mix function pointers with member-function pointers. However, you can accomplish what you want (and a lot more) by giving up on function pointers and turning to higher level "function objects" with libraries like Loki or Boost.Function (and Boost.Bind is quite handy when using Boost.Function as well!). http://www.boost.org[^]

William E. Kempf

valikac6-Jan-03 16:07

valikac

6-Jan-03 16:07

One solution is static declaration. Given assignFuncs points to a class member function, then that class member function must be static if you want to call it anytime and anywhere. Otherwise, you must call it via object.

Kuphryn

tilli again7-Jan-03 8:43

tilli again

7-Jan-03 8:43

Great! Making them static is working. To answer the question about "why the hassle": I'm writing on an Win32 API OOP Wrapper, and I wanted the user to be able to overwrite a function (assignFunc in this case) which is called by the class during the initialization process. What it does then is returning a list of Window Messages with their corresponding callback functions. Once a message needs to be processed then, the window message loop checks if the message has a callback defined and launches it. The reason I wanna be able to use class member functions for this purpose is so the callback functions can use member variables.

tilli

Tree Control Check Boxes... ???

tilli again8-Jan-03 8:18

tilli again

8-Jan-03 8:18

Well...making them static did work for what I wanted. But I'm no more able to access non-static functions from these functions then, so the intended advantage over non-class-functions will be exactly void. So, anyone has an idea how to rewrite the original code? I'd like to keep something at least somewhat similiar to the current approach, because I found it to be quite convenient and flexible for the user!

Thanks
tilli

work_to_live6-Jan-03 9:31

work_to_live

6-Jan-03 9:31

I inserted a tree control in a dialog box, and enabled the Check Boxes property. Then I load up the control with items, allow the user (me right now) to select some of them by placing checks next to the items of interest.

All is well and good. The only problem I have is... I can't figure out how to determine which items have been checked! Any help would be greately appreciated.

Thanks,
Gary H

Re: Tree Control Check Boxes... ???

work_to_live6-Jan-03 9:51

work_to_live

6-Jan-03 9:51

I found it...

I was looking at the item state, and didn't realize there was a GetCheck member function of CTreeCtrl. I knew it was going to be simple.

Later.

Synchronization.. do I need?

Subrahmanyam6-Jan-03 9:15

Subrahmanyam

6-Jan-03 9:15

I have a dialog based application in which I have two sources of events
1) On Timer
2) On User input(such as click of button)

Now on both events I will be calling a function, which acts on a single resource.
Calling the function while it is already executing is dangerous & can corrupt all my data.

Now I want to know do I need to put any synchronization code (SingleLock etc.) in my function.

** The important point here is that I am not creating any threads explicitly.
So my assumption is that my app is single threaded. In such case my function can never be called (from anywhere else) while it is running.

Am I correct? Am I missing anything here?

Please help me.

Re: Synchronization.. do I need?

Tim Smith6-Jan-03 10:17

Tim Smith

6-Jan-03 10:17

Since you only have one thread, you need not worry.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

Re: Synchronization.. do I need?

C^hris L^osinger6-Jan-03 10:59

C^hris L^osinger

6-Jan-03 10:59

you might not need SingleLock, etc.. but if there's a chance you could end up going through the same function twice at the same time (especially if you're doing message pumping) you might need to use a flag at the top of any functions where this could be dangerous.

bool g_alreadyInFuncA = false;

void funcA()
{
  if (g_alreadyInFuncA)
  {
    error? return early? crash?
  }

  g_alreadyInFuncA = true;

  blah 
  blah
  MessagePump...
  blah
  g_alreadyInFuncA = false;
}

void OnMyMessage()
{
 funcA()
}

-c

I'm not the droid you're looking for.

ThumbNailer

Debugging Mutexes?

clintsinger6-Jan-03 8:09

clintsinger

6-Jan-03 8:09

Hi All,

I was wondering where I would find information on the techniques for debugging mutexes, semaphores, critical sections etc. I have a place in my code that blocks and locks the application. It appears to be happening randomly on a CSingleLock(&mymutex). How do I takle it and find out what the real problem is?

Cheers,
Clint

Tim Smith6-Jan-03 8:39

Tim Smith

6-Jan-03 8:39

1. Are you 100% positive you are always unlocking your locks?
2. Do you have any deadly embraces in your locks. (i.e. thread #1 locks lock A then lock B while thread #2 locks lock B then lock A.)

Tim Smith

I'm going to patent thought. I have yet to see any prior art.

clintsinger6-Jan-03 8:47

clintsinger

6-Jan-03 8:47

As far as I know I don't have these problems. Would either problem cause random mutex lockups? I can see where #2 could potentially be the culprit as there looks like a race condition there.

Cheers,
Clint

Tim Smith6-Jan-03 10:16

Tim Smith

6-Jan-03 10:16

Both examples cause lockups. The first because some thread never released the mutex. The second for the race condition you saw.

Tim Smith

I'm going to patent thought. I have yet to see any prior art.