RE: [Dev-C++] Static members for callbacks

[Ioannis V. <no...@ho...>]

> -----Original Message-----
> From: Ioannis Vranos [mailto:no...@ho...] 
> Sent: Monday, July 29, 2002 10:34 AM
> To: 'Abhijit Shylanath'
> Cc: 'Dev-C++ Mailing List'
> Subject: RE: [Dev-C++] Static members for callbacks
> 
> 
> > -----Original Message-----
> > From: Abhijit Shylanath [mailto:mu...@gm...] 
> > Sent: Monday, July 29, 2002 9:50 AM
> > To: Ioannis Vranos
> > Cc: Dev-C++ Mailing List
> > Subject: Re: [Dev-C++] Static members for callbacks
> > 
> > 
> > > > You can't use non-static methods for windows callbacks (like in
> > > > CreateThread(), SetWindowsHookEx()) which need you to suppply
> > > > a call-back
> > > > function.
> > >
> > >
> > > This is too Win32 to me. What do you mean by call-back 
> > function. Can you
> > > provide a small concrete example?
> > 
> > 
> > Basically, typedef function_pointer call_back;
> > 
> > For example, in CreateThread(), the args are:
> > 
> > HANDLE CreateThread(
> >     LPSECURITY_ATTRIBUTES  lpThreadAttributes, // address of 
> > thread security
> > attributes
> >     DWORD  dwStackSize, // initial thread stack size, in bytes
> >     LPTHREAD_START_ROUTINE  lpStartAddress, // address of 
> > thread function
> >     LPVOID  lpParameter, // argument for new thread
> >     DWORD  dwCreationFlags, // creation flags
> >     LPDWORD  lpThreadId  // address of returned thread identifier
> >    );
> > 
> > Here, LPTHREAD_START_ROUTINE should be a function pointer 
> to a 32-bit
> > returning (void *) accepting function, as in
> > 
> >     DWORD my_thread_proc(void *some_arg);
> > 
> > where DWORD is, on Win32, unsigned long.
> 
> 
> 
> Ok then you can use a regular function to call the 
> appropriate member function. This regular function will 
> accept also your object as a parameter.


In general use an additional regular function. For example if your
function must have a specific return type and specific arguments like:

int s(void *);


You can use a third function *& a global variable e.g.


// The value of the data member of class A

int x;

inline void loadvalue(const A &a)
{
 x=a.getvalue();
}


// s now can read the global variable x


Of course this way sucks. But this is not a C++ problem, but Win32
problem which after all is C (or perhaps even pre-ANSI C).

In C there is some use of global variables like errno, although the use
of global variables is not recommended there too.


Ioannis

* Ioannis Vranos
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