IV86728: UNNECESSARY PRIVATE COPY CONSTRUCTOR WARNING

XL C/C++ for AIX, V13.1.3.3 Fix Pack (December 2016)
XL C/C++ for AIX, V13.1.3.4 Fix Pack (April 2017)
XL C/C++ for AIX, V13.1.3.5 Fix Pack (July 2018)
XL C/C++ for AIX, V13.1.3.6 Fix Pack (May 2019)

APAR status

• Closed as program error.

Error description

• An unexpected warning is output when compiling with the
  -qlanglvl=extended0x option to enable XLC's C++11 support
  related to copy constructor class visibility.
  
  
     === TEST CASE ===
  
  #include <iostream>
  #include <string>
  
  namespace copy
  {
   class CopyConstructor
   {
    private:
     std::string m_str;
  
     CopyConstructor(const CopyConstructor &){};
     CopyConstructor &operator=(const CopyConstructor &) {};
  
    public:
     CopyConstructor(const std::string &str) : m_str(str) { }
  
    const std::string & toString() const { return m_str; }
   };
  
   void MyFunction(const CopyConstructor &str) { }
  }
  
  int main()
  {
   copy::MyFunction(std::string("Hello"));
  }
  
  
  $ xlC_r test.cpp -qlanglvl=extended0x
  "test.cpp", line 25.26: 1540-0306 (W) The "private" copy
  constructor "CopyConstructor(const CopyConstructor &)" cannot be
  accessed.
  "test.cpp", line 25.26: 1540-0308 (I) The semantics specify that
  a temporary object must be constructed.
  "test.cpp", line 25.26: 1540-0309 (I) The temporary is not
  constructed, but the copy constructor must be accessible.
  "test.cpp", line 12.78: 1540-1101 (W) A return value of type
  "copy::CopyConstructor &" is expected.
  $
  

Local fix

• Use -qsuppress to suppress the individual warning messages.
  

Problem summary

• PROBLEM DESCRIPTION:
  An unnecessary warning was generated for the copy constructor.
  
  The warning is correct given the wording for C++03.  The
  reference binding goes through the non-reference copy
  initialization path, which involves a direct initialization
  step, technically requiring the copy constructor.  However, a
  warning in this case is no longer required for C++11.
  
  USERS AFFECTED:
  Users of the C++11 language level.
  

Problem conclusion

• The warning behaviour will remain the same for default C++03
  compiles.  The message generation is now disabled with the
  C++11 language level via -qlanglvl=extended0x .
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

• APAR is sysrouted TO one or more of the following:

  IV91673

Fix information

• Fixed component name

  XL C/C++ FOR AI

• Fixed component ID

  5725C7200

Applicable component levels