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  1. // Remove "x" to invoke feature.
  2. #define     xTEST_BAD_ASSIGN
  3.  
  4. #if defined( CPP11 )
  5. #   define OVERRIDE override
  6. #   define NOEXCEPT noexcept
  7. #else
  8. #   define OVERRIDE
  9. #   define NOEXCEPT throw()
  10. #endif
  11.  
  12. //---------------------------------------------------------------------------
  13. #include <assert.h>         // assert
  14. #include <algorithm>        // std::swap
  15. #include <exception>        // std::terminate
  16. #include <string>           // std::string
  17. #include <iostream>         // std::wcout, std::wcerr, std::endl
  18. using namespace std;
  19.  
  20. #define FATAL_ERROR( s ) \
  21.     assert( !s );  wcerr << s << endl;  terminate();
  22.  
  23. class Person
  24. {
  25. private:
  26.     string  name_;
  27.  
  28. public:
  29.     string name() const { return name_; }
  30.  
  31.     virtual void swapWith( Person& other ) NOEXCEPT
  32.     {
  33.         using std::swap; swap( name_, other.name_ );
  34.     }
  35.  
  36.     void operator=( Person other ) { swapWith( other ); }
  37.  
  38.     Person( string const& name )
  39.         : name_( name )
  40.     {}
  41. };
  42.  
  43. class Student
  44.     : public Person
  45. {
  46. private:
  47.     int     studentId_;
  48.  
  49.     virtual void swapWith( Person& ) NOEXCEPT OVERRIDE
  50.     {
  51.         FATAL_ERROR( "Student::swapWith( Person& ): dest. value slicing" );
  52.     }
  53.  
  54. public:
  55.     int studentId() const { return studentId_; }
  56.  
  57.     virtual void swapWith( Student& other ) NOEXCEPT
  58.     {
  59.         Person::swapWith( other );
  60.         using std::swap; swap( studentId_, other.studentId_ );
  61.     }
  62.  
  63.     void operator=( Student other ) { swapWith( other ); }
  64.  
  65.     Student( string const& name, int const studentId )
  66.         : Person( name ), studentId_( studentId )
  67.     {}
  68. };
  69.  
  70. wostream& operator<<( wostream& stream, string const& s )
  71. {
  72.     return (stream << s.c_str());
  73. }
  74.  
  75. int main()
  76. {
  77.     Person          a( "Hillary Clinton" );
  78.     Student         b1( "John Smith", 12345 );
  79.     Student         b2( "Mary Jones", 88888 );
  80.     Person&         bAsPerson = b1;      // OK.
  81.  
  82.     wcout
  83.         << "Name: " << b1.name()
  84.         << ". Student id: " << b1.studentId() << "."
  85.         << endl;
  86.  
  87. #ifdef TEST_BAD_ASSIGN
  88.     bAsPerson = a;              // Terminates at run-time (i.e. crash).
  89. #else
  90.     b1 = b2;                    // Good/allowed assignment.
  91. #endif
  92.  
  93.     wcout
  94.         << "Name: " << b1.name()
  95.         << ". Student id: " << b1.studentId() << "."
  96.         << endl;
  97. }
  98.  
Success #stdin #stdout 0.01s 2876KB
comments (?)
stdin
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Standard input is empty
stdout
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Name: John Smith. Student id: 12345.
Name: Mary Jones. Student id: 88888.
https://ideone.com/pAVJc
language:
C++ (gcc 8.3)
created:
12 years ago
visibility:
public

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