Re: copy ctor being private and compilation error
On 08/ 3/10 06:37 PM, Kai-Uwe Bux wrote:
Ian Collins wrote:
On 08/ 3/10 04:12 PM, subramanian100in@yahoo.com, India wrote:
Consider the following program x.cpp:
<snip>
Just to be more explicit, I recall the declaration of Test:
class Test
{
public:
explicit Test(int arg = 10);
ostream& writeTo(ostream& os) const;
private:
Test(const Test& rhs);
int val;
};
Note the private copy constructor.
int main()
{
const Test& ref = Test();
cout<< ref<< endl;
return EXIT_SUCCESS;
}
When I compile this program as
g++ -std=c++98 -pedantic -Wall -Wextra x.cpp
I get the following compilation error:
x.cpp: In function `int main()':
x.cpp:12: error: `Test::Test(const Test&)' is private
x.cpp:33: error: within this context
Though the copy ctor of Test is private, the statement
const Test& ref = Test();
involves only taking a 'const reference' to the temporary Test object
created by Test() on the RHS. Since only a reference is made, why does
this statement require the copy ctor ?
It appears to be a bug in the version (3.4.x?) of gcc you are using.
It's not a bug. The code is invalid in C++98 and C++03 by [8.5.3/5] which
requires the copy constructor to be visibile. The compiler is free (but not
required) to make a copy of the object before initializing the reference.
The bug is in newer g++ versions (starting with the 4.3 series or
thereabout).
Ah, OK. I missed "The constructor that would be used to make the copy
shall be callable whether or not the copy is actually done."
--
Ian Collins