[Bug c++/55437] New: Non-const copy constructor causes error - even if not called

[Bug c++/55437] New: Non-const copy constructor causes error - even if not called

[rockydowns0485 at msn dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55437

             Bug #: 55437
           Summary: Non-const copy constructor causes error - even if not
                    called
    Classification: Unclassified
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: rockydowns0485@msn.com


I believe the error below should not occur.  The copy constructor in question
is not exercised.  Moreover, making the copy constructor const also makes the
error not occur.



class String{
public:
    String(String& s){} // No error if this line is removed
    String(const char* s){}
};

int main(){
    String S = (char*)"Test";
    return 0;
}


test2.cpp: In function ‘int main()’:
test2.cpp:9: error: no matching function for call to ‘String::String(String)’
test2.cpp:5: note: candidates are: String::String(const char*)
test2.cpp:4: note:                 String::String(String&)

[Bug c++/55437] Non-const copy constructor causes error - even if not called

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55437

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> 2012-11-22 12:48:09 UTC ---
The program is ill-formed.


    String S = (char*)"Test";

is equivalent to


    String S = String((char*)"Test");

which requires an accessible copy constructor (or in C++11 move constructor)
that takes an rvalue argument (i.e. temporary). A non-const reference cannot
bind to a temporary, so your copy constructor is not viable.

The copy constructor must be accessible and viable even if the copy is elided
and the copy constructor is not used.

You'll get the same error from any conforming C++ compiler.