[Bug c++/40685] New: explicit constructor is used where only implicit ctors are allowed

[Bug c++/40685] New: explicit constructor is used where only implicit ctors are allowed

[kretz at kde dot org]

The following testcase fails on g++ 4.4.0 and 4.3.2:

#include <cstdlib>

enum Enum {
    Foo
};

class A
{
    public:
        A(int y) : x(y) {}
        explicit A(Enum) : x(1) {}

        int x;
};

static void fun(A a = Foo)
{
    if (a.x != static_cast<int>(Foo)) {
        abort();
    }
}

int main()
{
    fun();
    return 0;
}

If the A(int) ctor is removed the program does not compile, as is expected. If
the line "A a = Foo" appears inside the function instead of the parameter list
then g++ correctly uses the A(int) ctor.

While on that topic: The code above was meant to use the Enum ctor, it would be
nice if g++ emits a warning about the emitted code probably using the wrong
ctor.


-- 
           Summary: explicit constructor is used where only implicit ctors
                    are allowed
           Product: gcc
           Version: 4.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kretz at kde dot org
 GCC build triplet: x86_64-unknown-linux-gnu
  GCC host triplet: x86_64-unknown-linux-gnu
GCC target triplet: x86_64-unknown-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40685

[Bug c++/40685] explicit constructor is used where only implicit ctors are allowed

[kretz at kde dot org]

------- Comment #1 from kretz at kde dot org  2009-07-29 14:51 -------
I just tested with 4.4.1 and I can still confirm the problem.


-- 

kretz at kde dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to fail|                            |4.4.0 4.4.1 4.3.2 4.3.3


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40685

[Bug c++/40685] explicit constructor is used where only implicit ctors are allowed

[bangerth at gmail dot com]

------- Comment #2 from bangerth at gmail dot com  2009-08-25 14:39 -------
Hm, confusing:
-----------------------------
enum E {e};

struct A {
    A(int);
    explicit A(E) {};
};

int main () { A a = e; }
-----------------------------
This compiles but not links becase A::A(int) is called. If I remove
the explicit keyword, it calls A::A(E) and links fine. I must admit
that I don't know whether that's correct. icc concurs with gcc, by the way.

W.


-- 

bangerth at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40685

[Bug c++/40685] explicit constructor is used where only implicit ctors are allowed

[kretz at kde dot org]

------- Comment #3 from kretz at kde dot org  2009-08-25 15:26 -------
Actually I came across this problem because my code was failing on MSVC and
icc. Then I noticed that icc compiles the code, the one that I pasted,
differently. On further investigation I decided that gcc is at fault and that
my code was wrong (which I didn't notice because gcc made my wrong right again
:-) ).

I tested with icc 11.1 and MSVC 2008.

For the testcase you describe I thought gcc works correctly. I could only
reproduce the problem if the ctor is called as a default argument of a
function.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=40685