temporary object creation

Hi,

could someone please explain what the compiler attempts to do with the
following code? Why does it not create a temporary object instance of
type B?

Cheers, Martin.


struct A{};

struct B{
B(A a){}
};

int main(){
A a;
B(a); // error
// B((A)a); // compiles ok
return 0;
}


Comeau C/C++ 4.3.3 (Aug 6 2003 15:13:37) for ONLINE_EVALUATION_BETA1
Copyright 1988-2003 Comeau Computing. All rights reserved.
MODE:strict errors C++

"ComeauTest.c", line 9: error: "a" has already been declared in the
current scope
B(a); // error
^

"ComeauTest.c", line 9: error: no default constructor exists for class
"B"
B(a); // error
^

"ComeauTest.c", line 8: warning: variable "a" was declared but never
referenced
A a;
^

"ComeauTest.c", line 9: warning: variable "a" was declared but never
referenced
B(a); // error
^

2 errors detected in the compilation of "ComeauTest.c"


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"meigel" <martin.eigel@gmail.com> writes:

> could someone please explain what the compiler attempts to do with
> the following code? Why does it not create a temporary object
> instance of type B?
>
> Cheers, Martin.
>
>
> struct A{};
>
> struct B{
> B(A a){}
> };
>
> int main(){
> A a;
> B(a); // error

Because this statement is equivalent to this:

B a;

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meigel wrote:
> Hi,
>
> could someone please explain what the compiler attempts to do with the
> following code? Why does it not create a temporary object instance of
> type B?
>
> struct A{};
> struct B{
> B(A a){}
> };

> int main(){
> A a;
> B(a); // error
Because this is equivalent to
B (a);
Which defines a variable 'a' of type B. Also, you do not have a default constructor for
type B, thus the second error.

--

Valentin Samko - http://www.valentinsamko.com

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meigel wrote:
[snipped]
> int main(){
> A a;
> B(a); // error
> // B((A)a); // compiles ok
> return 0;
> }

Because B(a); is just about the same as B a;, which tries to creat an
object named a of type B. But a is already defined as of type A.

Ben

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