Re: Passing return value by reference
From: Andrey Tarasevich (andreytarasevich_at_hotmail.com)
Date: 06/14/04
- Next message: Partho Bhowmick: "Re: Question regarding the << operator"
- Previous message: Joe Laughlin: "Re: A few Coding Problems..."
- In reply to: Bob Hairgrove: "Re: Passing return value by reference"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Date: Mon, 14 Jun 2004 11:02:48 -0700
Bob Hairgrove wrote:
> On Fri, 11 Jun 2004 11:24:13 -0700, Andrey Tarasevich
> <andreytarasevich@hotmail.com> wrote:
>
>>red floyd wrote:
>>> ...
>>> Am I allowed to pass the anonymous temporary returned by f() to a
>>> function requiring a non-const reference?
>>
>>No.
>>
>>> I suspect G++ is correct, and VC is (again) braindead.
>>
>>VC supports this as an extension. The only reason it compiles on VC is
>>that you have this extension enabled. Disable it and VC will also issue
>>an error message.
>>
>>> class A
>>> {
>>> public:
>>> A() { }
>>> A(const A&) { }
>>> ~A() { }
>>> };
>>>
>>> A& operator<<(A& a, const char* p)
>>> {
>>> return a;
>>> }
>>>
>>> A f()
>>> {
>>> return A();
>>> }
>>>
>>> int main()
>>> {
>>> f() << "Hello";
>>> return 0;
>>> }
>>
>>You can make this compile by implementing 'operator<<' as a member
>>function of class 'A'. There's certain asymmetry in C++ behavior when it
>>comes to things like this...
>
> Doesn't the problem actually stem from the temporary A which is
> created from the temporary returned by f() in order to bind to the
> non-const reference argument declared by operator<<()?
Yes. That's the immediate reason for the error message, as was already
stated above. However, one way to work around the problem is, once
again, to implement 'operator<<' as a member function of class 'A'.
class A {
public:
...
A& operator<<(const char* p) { return *this; }
};
A f() {
return A();
}
int main() {
f() << "Hello"; // OK, no error
return 0;
}
C++ permits non-constant member function calls on temporary objects. I
can't say whether this is a viable solution in OP's case because all I
have is the above piece of abstract code.
-- Best regards, Andrey Tarasevich
- Next message: Partho Bhowmick: "Re: Question regarding the << operator"
- Previous message: Joe Laughlin: "Re: A few Coding Problems..."
- In reply to: Bob Hairgrove: "Re: Passing return value by reference"
- Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
Relevant Pages
|
