Re: Member function pointer to member function of another class
Praetorian wrote:
On Apr 2, 11:25 am, "jason.cipri...@gmail.com"
<jason.cipri...@gmail.com> wrote:
On Apr 2, 12:05 pm, Praetorian <ashish.sadanan...@gmail.com> wrote:
I
don't want ClassA'smemberfunctionto call ClassB'sfunctiondirectly
because ClassA can be used in 2 ways, one of which is a case in
which it does not create an instance of ClassB; hence by passing
afunction pointerI can handle that case easily.
...
classClassA {
public:
typedef BOOL (ClassA::*FPAbortFlag)(void);
...
m_fpAbort = (FPAbortFlag)(&(ClassB::GetFlagX));
You can not do what you are trying to do the way you are trying to do
it. Your code compiles with the explicit cast but will not
necessarily ...
[SNIP]
Jason,
I like the solution of creating another class that both the other
classes inherit from and have it handle the function pointers. The
problem with that implementation in my case is that both the classes I
described are in a DLL; the DLL has 2 interfaces, one which causes
ClassA to create an instance of ClassB or a second interface where the
ClassA member function in question must be able to accept a function
pointer (which may be to a member function of an arbitrary class). In
that case, it wouldn't be possible to have the user of the DLL
inheriting from a class which is hidden with the DLL itself. Maybe my
approach to this problem is incorrect; I'm not a C programmer, not
very good with C++, so there probably is a better way to do this. What
I ideally want is a C-like way of passing around function pointers
that can be called by anyone.
There is a problem with that. A class function has a hidden first parameter
called this which is a pointer to the instance of the class.
I.E.
class Foo
{
void MyFunc( int i );
};
MyFunc has a hidden first parameter this which would look like this if it
was spelled out:
void MyFunc( Foo* this, int i );
When you declare a class function pointer the compiler knows about the
hidden this pointer.
Now the problems.
You can not mix pointers between classes as you are trying to do because the
compiler has to know what parameters the function accepts. Is the first
parameter ClassA*, ClassB or no hidden first parameter (stand alone
function).
You might be able to get away with some form of void* as the first
parameter, but I doubt it. Also, what about stand alone functions that
don't have a hidden first parameter?
You might just want to go with stand alone function pointers and accept a
void* to the instance if required, although if this is a call back function
how is your calling function going to know what to place?
I think you might want to rethink your program design.
--
Jim Langston
tazmaster@rocketmail.com