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Guest
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 Posted: Mon May 14, 2007 8:17 am Post subject: class cross-reference |
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How does the compiler solve class cross-reference? Is it valid at all?
In the example below class A stores a reference to class B that stores
a reference to class A. Both references are set in the constructor.
The instantiation of the two class takes place in the constructor of
class C.
This piece of code worked for me in different compilers; however I
cannot understand how it is done.
Please make your comments!
Thanks!
class A {
public:
A(B& b) : mB(b) {}
private:
B& mB;
};
class B {
public:
B(A& a) : mA(a) {}
private:
A& mA;
};
class C {
public:
C() : mA(mB), mB(mA) {}
private:
A mA;
B mB;
};
int main() {
C myC;
return 0;
}
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Sebastian Redl
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| Posted: Mon May 14, 2007 4:37 pm Post subject: Re: class cross-reference |
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On Mon, 14 May 2007 gergomeister (AT) gmail (DOT) com wrote:
| Quote: | This piece of code worked for me in different compilers; however I
cannot understand how it is done.
|
And none gave you any warnings at all? Typically they warn about this.
It's not that it is undefined behaviour. Wehn A's constructor is called,
mB is uninitialized, but as long as A's constructor doesn't convert it to
an R-value or access any members of it, the behaviour is defined.
It's just that it's a potentially dangerous thing to do.
As for how it works, well, that's an implementation detail. Typical
implementations implement references as pointers, so A's constructor
simply receives the memory address where mB will be constructed later.
Sebastian Redl
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