RE: Pointer to a function forbid!!

RE: Pointer to a function forbid!!

[Glover George]

Thank you, but could you explain something to me ?  Is f the name of the
function I'm needing a pointer to, or is it ADDED to the class?  I'm not
quite sure how I use this.  Is m() the member function that I'm needing
the pointer to? I know I replace the A with the name of my class, but
I'm not sure which other items I'm supposed to substitute for.  Thanks a
lot man.




> -----Original Message-----
> From: sebastian-huber@web.de [mailto:sebastian-huber@web.de] 
> Sent: Friday, April 12, 2002 11:59 AM
> To: Glover George
> Subject: Re: Pointer to a function forbid!!
> 
> 
> Hello,
> if you want to avoid global variables, you can try this:
> 
> class A {
> public:
> 	static void f( void* thisPointer)
> 	{
> 		static_cast<A*>( thisPointer)->m();
> 	}
> 
> private:
> 	void m();
> };
> 
> This works a least with the POSIX thread functions.
> 
> On Thursday 11 April 2002 21:32, you wrote:
> > That's fine, I really just didn't know if I could attach 
> code on the 
> > list. Here's where I'm passing the address of 
> > gate.DeviceCallbakEventHandler() to a function (which is 
> part of the 
> > Intel UPnP SDK, I'll put it's declaration below).  See, I have some 
> > code that this works with, but its pure C.  The funtions 
> were defined 
> > before main (I mean at the top of the file that contains 
> main).  They 
> > didn't use the & before the function (which was just 
> > DeviceCallbackEventHandler), but if I don't include the &, 
> it says it 
> > can't find a matching function for int (*) (<paramaters>). 
> Candidates 
> > are int DeviceCallbackEventHandler(<parameters>).
> >
> > I know there can be pointers to functions, but I'm not 
> understanding 
> > why it won't work here.
> >
> > Muchas Gracias in advance!!!
> >
> > Int main (arc, argv**){
> > Gate gate;
> > .
> > .
> > .
> > if ((ret = UpnpRegisterRootDevice(desc_doc_url,
> > &gate.DeviceCallbackEventHandler,
> >                                 &gate.device_handle,
> > &gate.device_handle)) != UPNP_E_SUCCESS)
> >         {
> > 		...(SNIP)
> >         }
> > .
> > .
> > .
> > }
> > ///////Here is the class declaration for a Gate class.
> >
> > class Gate
> > {
> >         public:
> >                 Gate();
> >                 ~Gate();
> >
> >                 int DeviceStateTableInit(char *);
> >                 int DeviceHandleSubscriptionRequest (struct 
> > Upnp_Subscription_Request *sr_event);
> >                 int DeviceHandleGetVarRequest(struct 
> > Upnp_State_Var_Request *);
> >                 int DeviceHandleActionRequest(struct 
> > Upnp_Action_Request *);
> >                 int DeviceCallbackEventHandler(Upnp_EventType 
> > EventType, void*, void*);
> >
> >                 PortMapList m_list;
> >                 IPCon *m_ipcon;
> >                 char *gate_udn;
> >                 UpnpDevice_Handle device_handle;
> > };
> > ///////AND THE following is the declaration provide in the 
> Intel UPnP 
> > SDK for Linux
> >
> >
> > /** {\bf UpnpRegisterRootDevice} registers a device application with
> >  *  the UPnP API.  A device application cannot make any other API
> >  *  calls until it registers using this function.  Device 
> applications
> >  *  can also register as control points (see {\bf 
> UpnpRegisterClient}
> >  *  to get a control point handle to perform control point
> >  *  functionality).
> >  *
> >  *  {\bf UpnpRegisterRootDevice} is synchronous and does 
> not generate
> >  *  any callbacks.  Callbacks can occur as soon as this function 
> > returns.
> >  *
> >  *  @return An integer representing one of the following:
> >  *    \begin{itemize}
> >  *      \item {\tt UPNP_E_SUCCESS}: The operation completed
> > successfully.
> >  *      \item {\tt UPNP_E_FINISH}: The UPnP library is already
> > terminated or
> >  *                                 is not initialized.
> >  *      \item {\tt UPNP_E_INVALID_DESC}: The description 
> document was
> > not
> >  *              found or it does not contain a valid device 
> description.
> >  *      \item {\tt UPNP_E_INVALID_PARAM}: Either {\bf 
> Callback} or {\bf
> > Hnd}
> >  *              are not valid pointers or {\bf DescURL} is 
> {\tt NULL}.
> >  *      \item {\tt UPNP_E_NETWORK_ERROR}: A network error occurred.
> >  *      \item {\tt UPNP_E_SOCKET_WRITE}: An error or 
> timeout occurred
> > writing
> >  *              to a socket.
> >  *      \item {\tt UPNP_E_SOCKET_READ}: An error or timeout occurred
> > reading
> >  *              from a socket.
> >  *      \item {\tt UPNP_E_SOCKET_BIND}: An error occurred binding a
> > socket.
> >  *      \item {\tt UPNP_E_SOCKET_CONNECT}: An error 
> occurred connecting
> > the
> >  *              socket.
> >  *      \item {\tt UPNP_E_OUTOF_SOCKET}: Too many sockets 
> are currently
> >  *              allocated.
> >  *      \item {\tt UPNP_E_OUTOF_MEMORY}: There are insufficient
> > resources to
> >  *              register this root device.
> >  *    \end{itemize} */
> >
> > int UpnpRegisterRootDevice(
> >     IN const char *DescUrl,    /** Pointer to a string 
> containing the
> >                                    description URL for this 
> root device
> >                                    instance. */
> >     IN Upnp_FunPtr Callback,   /** Pointer to the callback 
> function for
> >                                    receiving asynchronous events. */
> >     IN const void *Cookie,     /** Pointer to user data 
> returned with
> > the
> >                                    callback function when 
> invoked. */
> >     OUT UpnpDevice_Handle *Hnd /** Pointer to a variable to 
> store the
> >                                    new device handle. */
> >     );
> >
> > > -----Original Message-----
> > > From: sebastian-huber@web.de [mailto:sebastian-huber@web.de]
> > > Sent: Thursday, April 11, 2002 1:42 PM
> > > To: Glover George
> > > Subject: Re: Pointer to a function forbid!!
> > >
> > >
> > > Hello,
> > > a bit of code might be helpful.
> > >
> > > On Thursday 11 April 2002 20:31, you wrote:
> > > > Hi, I was wondering if there is ANYWAY to overcome this
> > >
> > > error message
> > >
> > > > with G++;
> > > >
> > > > I have to pass a pointer to a function as a parameter to some 
> > > > other function.  However, the funtion I need to pass is a member
> > >
> > > function of
> > >
> > > > a class.  When I do, g++ complains with this.
> > > >
> > > > ISO C++ forbids taking the address of a bound member
> > >
> > > function to form
> > >
> > > > a pointer to member function.  Cannont convert ..... (snip)
> > > >
> > > > What exactly does this mean and why not?  The function is
> > >
> > > of an object
> > >
> > > > that has been initialized.  It is local to main however.
> > >
> > > Is it that
> > >
> > > > it needs to be created with a new before I can do it or is
> > >
> > > there just
> > >
> > > > absolutely no way to pass a pointer to a member function?
> > > >
> > > > Thank you.
> > > >
> > > > Glover George
> > > > Systems/Networks Admin
> > > > Gulf Sales & Supply, Inc.
> > > > (228) 762-0268
> > > > dime@gulfsales.com
> > > > http://www.gulfsales.com
> 

Re: Pointer to a function forbid!!

[Sebastian Huber]

Hello,
you take the pointer of the A::f() function, this functions calls then your 
member function via the handed over this pointer. This approach works only if 
the code that calls the funktion via the pointer passes an arbitrary object 
via a void pointer to the function, in our special case the this pointer.
The declaration of such functions is should be similar to void* (*f)(void*), 
at least for a function executed in a POSIX thread. I don't know if your 
handler functions works the same way. If not you have to use a globel object 
and a wraper function.

On Friday 12 April 2002 19:18, you wrote:
> Thank you, but could you explain something to me ?  Is f the name of the
> function I'm needing a pointer to, or is it ADDED to the class?  I'm not
> quite sure how I use this.  Is m() the member function that I'm needing
> the pointer to? I know I replace the A with the name of my class, but
> I'm not sure which other items I'm supposed to substitute for.  Thanks a
> lot man.
>
> > -----Original Message-----
> > From: sebastian-huber@web.de [mailto:sebastian-huber@web.de]
> > Sent: Friday, April 12, 2002 11:59 AM
> > To: Glover George
> > Subject: Re: Pointer to a function forbid!!
> >
> >
> > Hello,
> > if you want to avoid global variables, you can try this:
> >
> > class A {
> > public:
> > 	static void f( void* thisPointer)
> > 	{
> > 		static_cast<A*>( thisPointer)->m();
> > 	}
> >
> > private:
> > 	void m();
> > };
> >
> > This works a least with the POSIX thread functions.
> >
> > [...]

Segmentation fault!!

[Reggie Smith]

Hey everyone, I compiled a program on Red Hat Linux version 
6.2 using GCC 2.7.2. The program generates a hash for an 
index and it runs fine for several thousand iterations of 
adding to the index and then suddenly crashes with a 
segmentation fault error. Below is the error from DDD

Program received signal SIGSEGV, Segmentation fault.
0x400b8109 in chunk_free (ar_ptr=0x4014ccc0,
p=0x8516e38) at malloc.c:3111
3111	malloc.c: No such file or directory.
Current language:  auto; currently c
(gdb) 


Here also is the backtrace of the final three steps from DDD

Backtrace results:
#2 0x400b8564 in  __libc_realloc () at malloc.c:3254
#1 0x400b8b05 in chunk_realloc() at malloc.c:3424
#0 0x400b8109 in chunk_free() at malloc.c:3111


Below is the code for the index adding procedure with the 
error pointing at line DDD indicates the crash occured at. 
Note in this email the one line takes up two lines.


/* Function for adding a filled cell to the index */
/* Created by Bryan Wright */
 int addindex (int x, int y, int i) {
   unsigned int h = hash(x,y);
 -->  index[h] = (unsigned  int *)realloc((void 
*)index[h],entrysize[h]+1);
   index[h][entrysize[h]] = i;
   entrysize[h]++;
 }


Any ideas on what caused the problem? All help is 
appreciated.
Reggie

Re: Segmentation fault!!

[Ashish Gupta]

Hi,
This is a typical problem that occurs with memory leaks, trying to free 
a pointer for which no memory is allocated. From what seems from your 
description, you have forgotten to deallocate memory at some place and 
this is all the more difficult to detect if you use some containers to 
store pointers which are retrieved at a later time at which, if you 
choose to, you may destroy it to free the memory. Try using dmalloc to 
find out the possible memory leaks in your program and fix them. You can 
find dmalloc at
http://dmalloc.com

Cheers
Ashish Gupta


Reggie Smith wrote:

>Hey everyone, I compiled a program on Red Hat Linux version 
>6.2 using GCC 2.7.2. The program generates a hash for an 
>index and it runs fine for several thousand iterations of 
>adding to the index and then suddenly crashes with a 
>segmentation fault error. Below is the error from DDD
>
>Program received signal SIGSEGV, Segmentation fault.
>0x400b8109 in chunk_free (ar_ptr=0x4014ccc0,
>p=0x8516e38) at malloc.c:3111
>3111	malloc.c: No such file or directory.
>Current language:  auto; currently c
>(gdb) 
>
>
>Here also is the backtrace of the final three steps from DDD
>
>Backtrace results:
>#2 0x400b8564 in  __libc_realloc () at malloc.c:3254
>#1 0x400b8b05 in chunk_realloc() at malloc.c:3424
>#0 0x400b8109 in chunk_free() at malloc.c:3111
>
>
>Below is the code for the index adding procedure with the 
>error pointing at line DDD indicates the crash occured at. 
>Note in this email the one line takes up two lines.
>
>
>/* Function for adding a filled cell to the index */
>/* Created by Bryan Wright */
> int addindex (int x, int y, int i) {
>   unsigned int h = hash(x,y);
> -->  index[h] = (unsigned  int *)realloc((void 
>*)index[h],entrysize[h]+1);
>   index[h][entrysize[h]] = i;
>   entrysize[h]++;
> }
>
>
>Any ideas on what caused the problem? All help is 
>appreciated.
>Reggie
>
>
>
>

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   Sincerly yours,
   Ashish Gupta
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