1. Value Semantics CS-240 & CS-341 Dick Steflik

2. Value Semantics determine how the value(s) of one object are copied to another object in C++ the value semantics consist of the assignment operator and the copy constructor these allow assignment of one object to another and the creation of one object from another

3. for simple/static objects the default assignment operator and copy constructor will do what is needed; i.e. a member by member copy of the elements making up the object. class Date { public: Date(int m,int d, int y) private: int month,day,year } Date today(5,5,2000); Date May5(today); /* create May5 from today, default copy constructor */ Date May5th ; May5th = today; /* create an object called May5th then assign it a value, default assignment operator*/

4. for dynamic objects where the private data includes dynamically allocated data (ex. dynamic array) we must overload both the default copy constructor and the default assignment operator. class Stack{ public: Stack(); Stack (int size); Stack (const Stack & source); void operator = (const & source); private: int * data; int top; }

5. implementation Stack::Stack() /* default constructor */ { data = new int[10]; top = 0; } Stack::Stack(int size) /* constructor */ { data = new int[size]; top = 0; }

6. copy constructor create the object with the correct size, then copy the elements... Stack::Stack(const Stack & source) { int size = sizeof(source.data)/sizeof(int); /* calc the size */ data = new int[size]; /* allocate */ for (int i = 0 ; i < size; i++) /* copy the data */ data[i] = source[i]; top = source.top; /* copy the top pointer */ }

7. overload assignment operator calculate the size, discard the old data store, make a new one, then copy elements over... void Stack::operator = (const Stack * source) { int size = sizeof(source.data)/sizeof(int); delete data; data = new int[size]; for (int i=0 ; i< size ; i++) data[i] = source.data[i]; top = source.top; }