/*************** Vector.h **********************************/ #ifndef VECTOR_H #define VECTOR_H #include #include class Vector { private: unsigned long size; double *element; public: Vector(); Vector(unsigned long s); Vector(const Vector& v); // Copy constructor. // Initialize with a list of elements. Vector(std::initializer_list ls); ~Vector(); unsigned long getSize() const; void read(); double sum(); // Without & you can't do this: v[0] = 31 double& operator[](unsigned long i); Vector& operator=(const Vector& v); // Copy assignment. }; #endif /*************** Vector.cpp **********************************/ #include "Vector.h" Vector::Vector() { } Vector::Vector(unsigned long s) : size{s}, element{new double[s]} { for(unsigned long i = 0; i < s; ++i) element[i] = 0; } Vector::Vector(const Vector& v) : size{v.size}, element{new double[v.size]} // Allocating space for elements. { std::cout << "\nCOPY CONSTRUCTOR CALLED\n"; // Copy elements, at this point both vectors will not point // to the same address. Hence avoid memory leak and attempt // to double free. std::copy(v.element, v.element + v.size, element); } Vector::Vector(std::initializer_list lst) : size{lst.size()}, element{new double[lst.size()]} { std::copy(lst.begin(), lst.end(), element); std::cout << "Vector created with " << lst.size() << " elements\n"; } Vector::~Vector() { puts("DENTRO DEL DESCTURCTOR"); delete[] element; } unsigned long Vector::getSize() const { return size; } void Vector::read() { for(unsigned long i = 0; i < size; ++i) { std::cin >> element[i]; } } double Vector::sum() { double sum = 0.0; for(unsigned long i = 0; i < size; ++i) { sum += element[i]; } return sum; } double& Vector::operator[](unsigned long i) { if(i < 0 or size <= i) throw std::out_of_range{"Vector::operator[]"}; return element[i]; } Vector& Vector::operator=(const Vector& v) { std::cout << "\nCOPY ASSIGNMENT CALLED\n"; // Guard self assignment. if(this == &v) return *this; // Allocate new memory and copy its elements. double* new_elements = new double[v.size]; std::copy(v.element, v.element + v.size, new_elements); // Deallocate old memory. delete[] element; // Assign the new memory to the object. element = new_elements; size = v.size; // Returning the object we are pointing. return *this; } /*************** main.cpp **********************************/ #include #include "Vector.h" void good_copy(Vector v1) { // Bad copy is not happening because we have our copy constructor and // copy assignment, avoiding memberwise copy. // Copy constructor called. Vector v2 = v1; std::cout << "Elements of v2: "; for(unsigned long i = 0; i < v2.getSize(); ++i) { std::cout << v2[i] << " "; } std::cout << "\nFirst element of v2: " << v2[0] << '\n'; std::cout << "Changing value of v1[0]...\n"; v1[0] = 100; std::cout << "First element of v2: " << v2[0] << '\n'; v2[0] = 99; std::cout << "First element of v1: " << v1[0] << '\n'; // 100 std::cout << "First element of v2: " << v2[0] << '\n'; // 99 } int main() { int n; std::cout << "\nNumber of elements: "; std::cin >> n; Vector v1(n); v1.read(); good_copy(v1); // Copy constructor called. Vector v2; v2 = v1; // Copy assignment called. std::cout << "Elements of the vector v2 used by copy assignment: "; for(unsigned long i = 0; i < v2.getSize(); ++i) { std::cout << v2[i] << " "; } std::cout << '\n'; return 0; }

Copy constructor and copy assignment C++