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pico
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 Posted: Wed Jun 14, 2006 9:10 am Post subject: Pointer to class member |
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I am attempting to write an app that allows me to reference class
members from a structure. There is only one instance of this class so
I have no problem making the members (obj1, obj2, etc.) static. I can
get build the structure fine but Im having trouble dereferencing it.
My app runs under CE so I would really like the structure to be a const
to keep it in rom. Here is a simplified version of my code. Can
someone help me out?
class A{
public:
dosoething(){return 1};
};
class B{
public:
A obj1; // these can be made static
A obj2;
A obj3;
private: // or this can be public
INT somefunction();
};
struct objList{
A B::*objPtr;
int otherdata;
}
const objList bla[3]={{&B::obj1,10},{&B::obj1,20},{&B::obj3,30}};
INT B:somefunction{
int i;
for(i=0,i<3,i++){
(*(bla[i].objPtr)).dosomething();
}
} |
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Phlip
Guest
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| Posted: Wed Jun 14, 2006 9:10 am Post subject: Re: Pointer to class member |
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pico wrote:
| Quote: | I am attempting to write an app that allows me to reference class
members from a structure.
A B::*objPtr;
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That is a pointer-to-member. Not just a pointer. And it should be called a
"member offset", because it's not really a pointer.
| Quote: | const objList bla[3]={{&B::obj1,10},{&B::obj1,20},{&B::obj3,30}};
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And those are addresses of members (really offsets of members...).
| Quote: | (*(bla[i].objPtr)).dosomething();
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Okay. The highest precedence is i, so start there. i indexes bla to access
objPtr, which dereferences (*) _as_a_pointer_ to access dosomething().
Member pointers are not pointers, so * doesn't work. A member pointer always
needs another variable to supply the 'this'. So if you had aB, you might be
able to do this:
(aB .* bla[i].objPtr) . dosomething();
Next problem - why not simply use the Flyweight Design Pattern, so you can
get closer to bla[i].dosomething()? That would use virtual methods for what
they do, instead of rebuilding the virtual method system from scratch.
The answer is not "because it's for CE". It's easier to make beautiful code
small than small code beautiful.
--
Phlip
http://c2.com/cgi/wiki?ZeekLand <-- NOT a blog!!! |
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josh
Guest
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| Posted: Wed Jan 31, 2007 10:11 am Post subject: Re: pointer to class member |
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On 30 Gen, 16:53, Rolf Magnus <ramag...@t-online.de> wrote:
| Quote: | josh wrote:
Ok but when should I use this methodology?
Well, I have never needed to use a pointer to data member, and actually
don't know what I would need it for, but pointers to member functions on
the other hand can be useful e.g. for callback functions.
|
can you make, please, a concrete example? |
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