Question

I wrote an implementation of vector, which compiles but is not working properly according to the test main() program I was given.

I’m sure the error is in my push_back() function or my reserve() function but I’m not sure what exactly it is that’s wrong.

Can someone please look through the two functions and tell me if something is missing or needs to be changed?

#include <iostream>
#include <string>
#include <cassert>
#include <algorithm>
#include <cstring>



// Vector.h

using namespace std;

template <class T>
class Vector
{
public:

   typedef T * iterator;

   Vector();
   Vector(unsigned int size);
   Vector(unsigned int size, const T & initial);
   Vector(const Vector<T> & v);           // copy constructor//Done
   ~Vector();

   unsigned int capacity() const;         // return capacity of vector (in elements)//Done
   unsigned int size() const;             // return the number of elements in the vector//Done
   bool empty() const;

   iterator begin();                      // return an iterator pointing to the first element // Done
   iterator end();                        // return an iterator pointing to one past the last element //Done
   T & front();                           // return a reference to the first element //Done
   T & back();                            // return a reference to the last element //Done
   void push_back(const T & value);       // add a new element //Done
   void pop_back();                       // remove the last element //Done

   void reserve(unsigned int capacity);   // adjust capacity //Done
   void resize(unsigned int size);        // adjust size //Done

   T & operator[](unsigned int index);    // return reference to numbered element
   Vector<T> & operator=(const Vector<T> &);

private:
   unsigned int my_size;
   unsigned int my_capacity;
   T * buffer;
};

template<class T>//
Vector<T>::Vector()
{
    my_capacity = 0;
    my_size = 0;
    buffer = 0;
}

template<class T>
Vector<T>::Vector(const Vector<T> & v)
{
    my_size = v.my_size;
    my_capacity = v.my_capacity;
    buffer = new T[my_size]; 
    for (int i = 0; i < my_size; i++)
        buffer[i] = v.buffer[i];  
}

template<class T>//
Vector<T>::Vector(unsigned int size)
{
    my_capacity = size;
    my_size = size;
    buffer = new T[size];
}

template<class T>//
Vector<T>::Vector(unsigned int size, const T & initial)
{
    my_size;
    my_capacity = size;
    buffer = new T [size];
    for (int i = 0; i < size; i++)
        buffer[i] = initial;
}

template<class T>//
Vector<T> & Vector<T>::operator = (const Vector<T> & v)
{
    delete[ ] buffer;
    my_size = v.my_size;
    my_capacity = v.my_capacity;
    buffer = new T [my_size];
    for (int i = 0; i < my_size; i++)
        buffer[i] = v.buffer[i];
    return *this;
}

template<class T>//
typename Vector<T>::iterator Vector<T>::begin()
{
    return buffer;
}

template<class T>//
typename Vector<T>::iterator Vector<T>::end()
{
    return buffer + size();
}

template<class T>//
T& Vector<T>::Vector<T>::front()
{
    return buffer[0];
}

template<class T>//
T& Vector<T>::Vector<T>::back()
{
    return buffer[size - 1];
}

template<class T>
void Vector<T>::push_back(const T & v)
{
    if (my_size >= my_capacity)
    reserve(my_capacity +5);
    buffer [my_size++] = v;
}

template<class T>//
void Vector<T>::pop_back()
{
    my_size--;
}

template<class T>//
void Vector<T>::reserve(unsigned int capacity)
{
    if(buffer == 0)
    {
        my_size = 0;
        my_capacity = 0;
    }    
    if (capacity <= my_capacity)
    return;
    T * new_buffer = new T [capacity];
    assert(new_buffer);
    copy (buffer, buffer + my_size, new_buffer);
    my_capacity = capacity;
    delete[] buffer;
    buffer = new_buffer;

}

template<class T>//
unsigned int Vector<T>::size()const
{
    return my_size;
}

template<class T>//
void Vector<T>::resize(unsigned int size)
{
    reserve(size);
    my_size = size;
}

template<class T>//
T& Vector<T>::operator[](unsigned int index)
{
    return buffer[index];
}  

template<class T>//
unsigned int Vector<T>::capacity()const
{
    return my_capacity;
}

template<class T>//
Vector<T>::~Vector()
{
    delete[]buffer;
}

int main()
{  

   Vector<int> v;

   v.reserve(2);
   assert(v.capacity() == 2);

   Vector<string> v1(2);
   assert(v1.capacity() == 2);
   assert(v1.size() == 2);
   assert(v1[0] == "");
   assert(v1[1] == "");

   v1[0] = "hi";
   assert(v1[0] == "hi");

   Vector<int> v2(2, 7);
   assert(v2[1] == 7);

   Vector<int> v10(v2);
   assert(v10[1] == 7);

   Vector<string> v3(2, "hello");
   assert(v3.size() == 2);
   assert(v3.capacity() == 2);
   assert(v3[0] == "hello");
   assert(v3[1] == "hello");

   v3.resize(1);
   assert(v3.size() == 1);
   assert(v3[0] == "hello");

   Vector<string> v4 = v3;
   assert(v4.size() == 1);
   assert(v4[0] == v3[0]);
   v3[0] = "test";
   assert(v4[0] != v3[0]);  
   assert(v4[0] == "hello");

   v3.pop_back();
   assert(v3.size() == 0);

   Vector<int> v5(7, 9);
   Vector<int>::iterator it = v5.begin();
   while (it != v5.end())
   {
      assert(*it == 9);
      ++it;
   }

   Vector<int> v6;
   v6.push_back(100);
   assert(v6.size() == 1);
   assert(v6[0] == 100);
   v6.push_back(101);
   assert(v6.size() == 2);
   assert(v6[0] == 100);
   v6.push_back(101);

   cout << "SUCCESS\n";
}

Answer 1

At a first glance this line my_size; in Vector<T>::Vector(unsigned int size, const T & initial) strike me as very odd. You probably meant it to be my_size = size;