Hi all,
Here is what I am trying to do. I have a parent class calling a child
class. when one function in child class is called, i need to call
parent class' function. How can I get parent class' pointer?
Thx
Paul 5 27600
"Paul" <pc******@yahoo .com> wrote... Here is what I am trying to do. I have a parent class calling a child class. when one function in child class is called, i need to call parent class' function. How can I get parent class' pointer?
First of all, try to understand that you're not in Java any more.
There is no concept of "parent class" in C++. If you're talking
of a nested class and enclosing class, then they are unrelated.
In the code:
struct Enclosing {
struct Nested {
void foo();
};
};
an object of type Enclosing does not contain a subobject Nested.
The relationship between them is purely descriptional. In the
code:
struct Enclosing {
struct Nested {
void foo();
};
Nested nested;
void bar();
};
'nested' is a data member of type Nested in an Enclosing object.
If, when executing Enclosing::bar( ), you need to execute the
Nested::foo, and in that function you need to get to the object
of type Enclosing that called it, simply pass it as an argument:
void Enclosing::bar( )
{
nested.foo(this );
}
[of course, 'Nested::foo' has to be corrected to accept one
argument, of type Enclosing* :
struct Enclosing {
struct Nested {
void foo(Enclosing*) ;
};
Nested nested;
void bar();
};
Victor
Victor,
I am moving from VB to C++, and I am just starting to learn about C++
Classes. I am not sure I understand the following: In the code: struct Enclosing { struct Nested { void foo(); }; };
an object of type Enclosing does not contain a subobject Nested. The relationship between them is purely descriptional.
So, this does _not_ mean that Nested is in the scope of Enclosing? So from
global/file scope (not from inside the class Enclosing), how would you
declare a variable of type Nested?
Enclosing::Nest ed nested;
or
Nested nested;
or is it unavailable?
Thanks,
Jeremy
"Jeremy Cowles" <jeremy.cowle s[nosp@m]asifl.com> wrote... I am moving from VB to C++, and I am just starting to learn about C++ Classes.
Sorry about my note on Java, then. There is a significant difference
in nested classes' implementation between those two. I suppose that
between VB and C++ there might be a similar one.
I am not sure I understand the following:
In the code: struct Enclosing { struct Nested { void foo(); }; };
an object of type Enclosing does not contain a subobject Nested. The relationship between them is purely descriptional. So, this does _not_ mean that Nested is in the scope of Enclosing?
In scope, yes. However, unlike in Java (and I don't know about VB),
when you create an instance of 'Enclosing', C++ doesn't automatically
create an instance of 'Nested'.
So from global/file scope (not from inside the class Enclosing), how would you declare a variable of type Nested?
Enclosing::Nest ed nested;
Sure. Qualified name should work anywhere.
or Nested nested;
Yes, if you're inside the scope of 'Enclosing' class. or is it unavailable?
It's available alright. I described the difference above.
Victor
"Mike Smith" <mi************ *******@acm.DOT .org> wrote... Victor Bazarov wrote:
"Paul" <pc******@yahoo .com> wrote...
Here is what I am trying to do. I have a parent class calling a child class. when one function in child class is called, i need to call parent class' function. How can I get parent class' pointer?
First of all, try to understand that you're not in Java any more.
There is no concept of "parent class" in C++. If you're talking of a nested class and enclosing class, then they are unrelated.
ICBW but I got the impression that what he's calling "parent" and "child" would translate into "base" and "derived" in C++, not "enclosing" and "nested".
I agree that "base-derived" is a more commonly accepted meaning of
"parent-child" than "enclosing-nested", however, there are others:
in a tree a node closer to the root is often called 'a parent', in
a process communication the one that initiates the other is a parent,
the initiated is the child, in windows-driven UI, windows are often
placed in a tree-like hierarchy as well, perhaps since there exist
so many different applications of the terms "parent-child", the C++
language definition doesn't make any use of it.
Victor
"Jeremy Cowles" <jeremy.cowle s[nosp@m]asifl.com> wrote... [...] Just FYI, VB does not automatically create an instance for you, and based
on what you said, VB works the same in terms of scope as well.
Good info. Off-topic, but good info, thanks. This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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