Help With Vector Implementation in C++

[failbot]

I recently wrote an implementation of STL Vector as a programming exercise. The program compiles but I receive a strange error saying:

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

I've never come up with this error before and am not sure what exactly should be changed within my implementation to make it function correctly.

Can someone take a look through my code and see if anything jumps out at them as wrong in this specific case? I am sure that the problem is either in my push_back function or in my copy constructor. thanks in advance.

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

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";
}

[Taywin]

In line 42, you declare buffer as a pointer of T type. In line 50, you allocate an integer to the buffer. Then in line 58, you are using it as a pointer again???

[vijayan121]

There is a typo on line 74. Should be my_size = size ; Also, in your operator=(), you need to check for a trivial self-assignment. http://yosefk.com/c++fqa/assign.html