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Guest
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 Posted: Mon Feb 27, 2006 7:06 am Post subject: How can I keep reference to an input parameter of a function |
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I have a function in a class:
void A::aFunction (B& b) {
// do something
....
}
void A::anotherFunction() {
// need a reference of B again.
}
my question is how can I create an attriubte of A which can hold B
after A::aFunction() is called?
I can't create a reference of B as an attribute of A (since aFunciton
is not called during constructor of A).
Thanks for any idea. |
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Markus Moll
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| Posted: Mon Feb 27, 2006 7:06 am Post subject: Re: How can I keep reference to an input parameter of a func |
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Hi
Allerdyce.John (AT) gmail (DOT) com wrote:
| Quote: | I have a function in a class:
void A::aFunction (B& b) {
// do something
...
}
void A::anotherFunction() {
// need a reference of B again.
}
my question is how can I create an attriubte of A which can hold B
after A::aFunction() is called?
I can't create a reference of B as an attribute of A (since aFunciton
is not called during constructor of A).
|
There are reference wrappers (boost::reference_wrapper), or you could write
one yourself. It's basically struct wrapper { B& ref; wrapper(B& ref) :
ref(ref) {} };
But I don't like the whole idea of caching some B in A, as it relies on the
user's first calling aFunction. Why not return some object from aFunction
on which you can invoke anotherFunction?
Markus |
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Gianni Mariani
Guest
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| Posted: Mon Feb 27, 2006 7:06 am Post subject: Re: How can I keep reference to an input parameter of a func |
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Allerdyce.John (AT) gmail (DOT) com wrote:
| Quote: | I have a function in a class:
void A::aFunction (B& b) {
// do something
...
}
void A::anotherFunction() {
// need a reference of B again.
}
my question is how can I create an attriubte of A which can hold B
after A::aFunction() is called?
I can't create a reference of B as an attribute of A (since aFunciton
is not called during constructor of A).
Thanks for any idea.
|
Using a pointer ... somthing like so ?
struct B;
struct A
{
B * m_b;
A()
: m_b(0)
{}
void aFunction (B& b)
{
m_b = &b;
}
void anotherFunction()
{
assert( m_b );
B & b = * m_b;
}
}; |
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Guest
|
| Posted: Mon Feb 27, 2006 11:06 am Post subject: Re: How can I keep reference to an input parameter of a func |
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Allerdyce.John (AT) gmail (DOT) com wrote:
| Quote: | I have a function in a class:
void A::aFunction (B& b) {
// do something
...
}
void A::anotherFunction() {
// need a reference of B again.
}
my question is how can I create an attriubte of A which can hold B
after A::aFunction() is called?
|
Do you really need it? What if the B object is destroyed after
A::aFunction
returns? What if aFunction is called twice? Which B is needed then?
You might be able to hold a copy of B. If it's designed properly, it
will have
a copy constructor if and only if you can copy it. Of course, that
means that
anotherFunction will work on a copy of b, but at least A can ensure the
lifetime of that copy.
A proper design would probably involve a smart pointer. Either
std::auto_ptr<B>,
boost::shared_ptr<B> or std::tr1::shared_ptr<B> could work.
HTH,
Michiel Salters |
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Tomás
Guest
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| Posted: Mon Feb 27, 2006 5:06 pm Post subject: Re: How can I keep reference to an input parameter of a func |
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posted:
| Quote: |
I have a function in a class:
void A::aFunction (B& b) {
// do something
...
}
void A::anotherFunction() {
// need a reference of B again.
}
my question is how can I create an attriubte of A which can hold B
after A::aFunction() is called?
I can't create a reference of B as an attribute of A (since aFunciton
is not called during constructor of A).
Thanks for any idea.
|
Add the following to A:
class A
{
protected:
B* p_b;
};
Then write the functions as follows:
void A::aFunction (B& b)
{
p_b = &b;
}
Then to use it as a reference in another function:
void A::anotherFunction()
{
B& b = *p_b;
//Now we can use "b" as we please:
b.EatGrass();
FunctionThatTakesB( b );
}
-Tomás |
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