stack overflow when using copy constructor and/or assignment operator with string in c++

Question

i'm trying to run insertion sort on a simple class of my own making, which features a couple fields (int, float, and string) as well as a copy constructor, assignment operator, and '>' operator.

however, i'm getting a stack overflow when i run the code below. visual studio tells me its coming from the getName() function in my 'Student' class. the error originates from the assignment in my insertion sort function arr[i + 1] = arr[i];

anyone know why this is? i'm relatively new to c++, coming from mostly a java background.

#include <iostream>
#include <vector>
#include <string>
using namespace std;

class Student {
public:
    Student(string nm, int ID, float avg): name(nm), studentID(ID), overallAverage(avg) {}

    Student(const Student& rhs) : name(rhs.getName()), studentID(rhs.getStudentID()), overallAverage(rhs.getOverallAverage()) {}

    // copy and swap idiom
    Student& operator=(const Student& rhs) {
        Student copy = rhs;  // places a copy of rhs into copy using the copy constructor (copy will be cleaned up on return)
        swap(*this, copy); // move copy or rhs into this, this is a pointer to current object, *this dereferences the pointer
        return *this; 
    }
    ~Student() {}

    bool operator>(const Student& rhs) {
        if (rhs.getOverallAverage() > overallAverage)
            return false;
        else return true; 
    }

    string getName()const { return name; }
    int getStudentID()const { return studentID;  }
    float getOverallAverage()const { return overallAverage; }

private:
    string name; 
    int studentID; 
    float overallAverage; 

};

template<typename T> 
vector<T>& insertionSort(vector<T>& arr){
    for (int j = 1; j < arr.size(); j++) {
        T key = arr[j]; 
        int i = j - 1; 
        while (i > -1 && arr[i] > key) {
            arr[i + 1] = arr[i]; 
            i = i - 1; 
        }
        arr[i + 1] = key; 
    }
    return arr; 
}


int main()
{
    vector<Student> students = {Student("russ",0,89),Student("Seb",1,75),Student("julia",2,85),
                                Student("johnny",3,90),Student("Sushma",4,55)}; 

    students = insertionSort(students); 

    for (int i = 0; i < students.size(); i++) {
        cout << students[i].getName() << ", ";
    }
    cout << endl;  
}

original operator= from txtbook i'm using:

IntCell & operator= ( const IntCell & rhs ) // Copy assignment
{
IntCell copy = rhs;
std::swap( *this, copy );
return *this;
}

Your operator = calls std::swap, which calls your operator =, which calls std::swap, which calls your operator =, which calls std::swap ... — PaulMcKenzie
– PaulMcKenzie, Commented Jan 11, 2020 at 21:23
really? i coped that operator= directly from a well-known c++ textbook : edit-> put the textbook's operator= at bottom of my original question — Russell Butler
– Russell Butler, Commented Jan 11, 2020 at 21:28
In that book, did the class have its own swap function? If so, that is what prevented the infinite recursion. The std::swap will use the class swap function. — PaulMcKenzie
– PaulMcKenzie, Commented Jan 11, 2020 at 21:30
ah, i see you're right. upon re-reading that section it mentions: "t. Notice that if swap were implemented using the basic copy algorithm in Figure 1.14, the copy-and-swap idiom would not work, because there would be mutual nonterminating recursion. In C++11 we have a basic expectation that swapping is implemented either with three moves or by swapping member by member" — Russell Butler
– Russell Butler, Commented Jan 11, 2020 at 21:34
A generic routine like std::swap requires that the arguments be Swappable, and obviously your Student class was not, until a custom Student::swap function is created. — PaulMcKenzie
– PaulMcKenzie, Commented Jan 11, 2020 at 21:44

PaulMcKenzie · Accepted Answer · 2020-01-11 21:35:14Z

2

The infinite recursion is caused by std::swap calling Student::operator=, which calls std::swap, which calls Student::operator=, etc.

To alleviate this, write your own swap function that calls std::swap on each of the members:

class Student
{
//...
   void swap(Student& left, Student& right)
    {
        std::swap(left.name, right.name);
        std::swap(left.studentID, right.studentID);
        std::swap(left.overallAverage, right.overallAverage);
    }
//...
};

answered Jan 11, 2020 at 21:35

PaulMcKenzie

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2 Comments

Russell Butler Over a year ago

thanks. it works now. the std::swap didn't work (error - no instance of overloaded function std::swap matches the argument list) so i just did left.name = right.name, etc. is this bad?

PaulMcKenzie Over a year ago

See what std::swap expects the arguments to be.

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