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Tip of the Day
Language: C++
Expertise: All
Mar 18, 1999

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Before You Define a Copy Constructor and Assignment Operator...

In general, classes that possess pointers, file handles, and other resources need a user-defined constructor to avoid aliasing. For example:
 
class Person {
private:
  int age;
  char * name;
public:   // the following three member functions must be defined by the class implementer 
  Person (const char * name, int age);
  Person & operator= (const Person & other); 
  Person (const Person& other);
};
Seemingly, there's no escape from explicitly defining a copy constructor and assignment operator for class Person, or else the compiler-generated copy constructor and assignment operator will result in aliasing. However, the aliasing problem in this case results from the reliance on low-level language constructs (a bare pointer). Had class Person possessed an embedded std::string object instead of a pointer to char, the user-written copy constructor and assignment operator wouldn't be needed. When a class needs user-defined assignment operator and copy constructor, it may indicate a design flaw rather than an unavoidable necessity.
Danny Kalev
 
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