Re: Object instantiation gets parsed as func.def.?
From: Doug Harrison [MVP] (dsh_at_mvps.org)
Date: 12/06/04
- Next message: manju: "Rendering elements in DHTML browser when created programmatically"
- Previous message: Agoston Bejo: "Object instantiation gets parsed as func.def.?"
- In reply to: Agoston Bejo: "Object instantiation gets parsed as func.def.?"
- Messages sorted by: [ date ] [ thread ]
Date: Mon, 06 Dec 2004 16:05:07 -0600
Agoston Bejo wrote:
>Hi! This is the smallest example I was able to create to demonstratet the
>problem. It seems that a certain kind of object instantiation gets parsed as
>a function definition (or whatever) by the compiler. I don't know if it
>comes from some (maybe not-so-)dark corner of the C++ standard, or VC7.1 has
>got a bug.
The "dark corner" theory is correct.
>Thx,
>Agoston
>
>//-----------------------------------
>template<typename T>
>struct A {
> A(T t):t(t) {}
> T t;
>};
>
>template<typename T> void f()
>{
> cout << T() << endl;
> A<T> a1((T()));
> A<T> a2(T()); // function definition?
> cout << a1.t << endl;
> cout << a2.t << endl; // compile error! (*)
>}
>
>int _tmain(int argc, _TCHAR* argv[])
>{
> f<int>();
> return 0;
>}
>
>// (*) error message:
>// error C2228: left of '.t' must have class/struct/union type
>// type is 'overloaded-function'
>// see reference to function template instantiation
>// 'void f<int>(void)' being compiled
>
>//--------------------------------------------
VC is correct. This is what Scott Meyers described as a "vexing parse" in
"Effective STL". To simplify:
int f(int());
This declares a function f that has one parameter of the type:
int (*)();
That is, the parameter is unnamed and has type "pointer to a function that
has no parameters and returns int".
You've already discovered one way to get the effect you're after, namely
parenthesizing the ctor argument.
-- Doug Harrison Microsoft MVP - Visual C++
- Next message: manju: "Rendering elements in DHTML browser when created programmatically"
- Previous message: Agoston Bejo: "Object instantiation gets parsed as func.def.?"
- In reply to: Agoston Bejo: "Object instantiation gets parsed as func.def.?"
- Messages sorted by: [ date ] [ thread ]
Relevant Pages
|
