Question

I just got a seg fault in overloading the assignment operator for a class FeatureRandomCounts, which has _rects as its pointer member pointing to an array of FeatureCount and size rhs._dim, and whose other date members are non-pointers:

FeatureRandomCounts &  FeatureRandomCounts::operator=(const FeatureRandomCounts &rhs)  
{  
  if (_rects) delete [] _rects;  

  *this = rhs;  // segment fault

  _rects = new FeatureCount [rhs._dim];  
  for (int i = 0; i < rhs._dim; i++)  
  {  
    _rects[i]=rhs._rects[i];  
  }  

  return *this;    
}

Does someone have some clue? Thanks and regards!

Answer 1

As mentioned, you have infinite recursion; however, to add to that, here’s a foolproof way to implement op=:

struct T {
  T(T const& other);
  T& operator=(T copy) {
    swap(*this, copy);
    return *this;
  }
  friend void swap(T& a, T& b);
};

Write a correct copy ctor and swap, and exception safety and all edge cases are handled for you!

The copy parameter is passed by value and then changed. Any resources which the current instance must destroy are handled when copy is destroyed. This follows current recommendations and handles self-assignment cleanly.

---

#include <algorithm>
#include <iostream>

struct ConcreteExample {
  int* p;
  std::string s;

  ConcreteExample(int n, char const* s) : p(new int(n)), s(s) {}
  ConcreteExample(ConcreteExample const& other)
  : p(new int(*other.p)), s(other.s) {}
  ~ConcreteExample() { delete p; }

  ConcreteExample& operator=(ConcreteExample copy) {
    swap(*this, copy);
    return *this;
  }

  friend void swap(ConcreteExample& a, ConcreteExample& b) {
    using std::swap;
    //using boost::swap; // if available
    swap(a.p, b.p); // uses ADL (when p has a different type), the whole reason
    swap(a.s, b.s); // this 'method' is not really a member (so it can be used
                    // the same way)
  }
};

int main() {
  ConcreteExample a (3, "a"), b (5, "b");
  std::cout << a.s << *a.p << ' ' << b.s << *b.p << '\n';
  a = b;
  std::cout << a.s << *a.p << ' ' << b.s << *b.p << '\n';
  return 0;
}

Notice it works with either manually managed members (p) or RAII/SBRM-style members (s).