Copy Constructor Needed with temp object

Question

The following code only works when the copy constructor is available.

When I add print statements (via std::cout) and make the copy constructor availa

Answer 1

From http://gcc.gnu.org/gcc-3.4/changes.html

When binding an rvalue of class type to a reference, the copy constructor of the class must be accessible. For instance, consider the following code:

class A 
{
public:
  A();

private:
  A(const A&);   // private copy ctor
};

A makeA(void);
void foo(const A&);

void bar(void)
{
  foo(A());       // error, copy ctor is not accessible
  foo(makeA());   // error, copy ctor is not accessible

  A a1;
  foo(a1);        // OK, a1 is a lvalue
}

This might be surprising at first sight, especially since most popular compilers do not correctly implement this rule (further details).

This will be fixed in C++1x by Core Issue 391.