Operator overloading trouble

Question

I'm having trouble figuring out how to properly overload the '=' operator to assign one student's information to another's for one of my assignments. I'm new to this, so I could have messed it up big time. Thanks for any help!

#include <iostream> using namespace std; class Student { public: void input() { cout << "Please enter student's name: "; cin >> name; cout << "Please enter the number of classes " << name << " is taking: "; cin >> numClasses; classList = new string[numClasses]; cout << "Please enter the list of classes " << name << " is taking: "; for(int i = 0; i < numClasses; i++) { cin >> classList[i]; } } void print() { cout << "Student's name: " << name << endl; cout << "Number of classes " << name << " is taking: " << numClasses << endl; cout << "List of classes " << name << " is taking: " << endl; for(int i = 0; i < numClasses; i++) { cout << classList[i] << endl; } } void resetClasses() { name.clear(); numClasses = 0; delete [] classList; } Student operator= (Student s) { Student temp; temp.name = s.name; temp.numClasses = s.numClasses; temp.classList = s.classList; return temp; } private: string name; int numClasses; string *classList; }; int main() { Student s1, s2; s1.input(); cout << "Student 1's data:" << endl; s1.print(); s2 = s1; cout << endl << "Student 2's data after assignment from student 1: " << endl; s2.print(); s1.resetClasses(); cout << endl << "Student 1's data after reset:" << endl; s1.print(); cout << endl << "Student 2's data, should still have original classes: " << endl; s2.print(); }

Make classList an std::vector<std::string> and you don't have to provide assignment operator, copy constructor, destructor, anything... — juanchopanza
– juanchopanza, Commented Apr 3, 2014 at 19:08
Your class lacks a user-defined destructor to clean up the memory, let alone an assignment operator and copy constructor. — PaulMcKenzie
– PaulMcKenzie, Commented Apr 3, 2014 at 19:14

Bathsheba · Accepted Answer · 2014-04-03 19:12:06Z

The correct way to implement the assignment operator is to use

Student& operator=(const Student& s){ if (&s != this){ this->name = s.name; /*etc for all members*/ } return *this; }

A few things to note:

The s to copy is passed by constant reference. That means that it does not take a deep copy nor is allowed to be modified by the function.
Return *this allows you to do multiple assignments: a = b = c;
The if statement circumvents any problems arising from self-assignment.
Pay special attention to the copying of classList. Ensure a deep copy is taken.

But It's far better to use the standard template library containers so you can rely on the compiler-generated assignment operator.

@fritzone: Possibly; hence my rather vague /*etc for all members*/. But I felt that was a b-type question. Let's get the form of the assignment operator sorted first.

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