// MT3Q1.cpp

#include <iostream>
#include <sstream>
#include <vector>

std::string convert(size_t i)
{
  std::ostringstream temp;
  temp << i;
  return temp.str();
}

typedef std::string Message;

class MessagePool
{
public:
  // create empty pool
  MessagePool(size_t poolSize) : numCreated(0), MAX(poolSize) {}
  size_t size() const { return pool_.size(); }
  // retrieve message
  Message* getMessage()
  {
    // if pool is empty
    if(pool_.size() == 0)
    {
      // if have not reached MAX messages
      if(numCreated < MAX)
      {
        // create message and return it
        ++numCreated;
        std::string temp = std::string("message #") + convert(numCreated);
        return new Message(temp);
      }
      else
        // otherwise return failure as null message
        return 0;
    }
    else
    {
      // otherwise get message from pool and return it
      Message* pMsg = pool_.back();
      pool_.pop_back();
      return pMsg;
    }
    return 0;
  }
  void releaseMessage(Message* pMsg)
  {
    // if pool not full
    if(pool_.size() < MAX && pMsg != 0)
      // return message to pool
      pool_.push_back(pMsg);
  }
private:
  std::vector< Message* > pool_;
  size_t MAX;
  size_t numCreated;
};

void main()
{
  MessagePool mp(5);
  Message* MessagePointerArray[7];
  for(int i=0; i<7; ++i)
  {
    Message* pObj = mp.getMessage();
    MessagePointerArray[i] = pObj;
    if(pObj)
      std::cout << "\n  " << *pObj ;
    else
      std::cout << "\n  " << "null message";
  }

  std::cout << "\n  pool size is " << mp.size();
  for(size_t i=0; i<3; ++i)
  {
    std::cout << "\n  -- releasing message: " << *MessagePointerArray[i];
    mp.releaseMessage(MessagePointerArray[i]);
  }
  size_t count = mp.size();
  std::cout << "\n  pool size is " << count;
  for(size_t i=0; i<count; ++i)
    std::cout << "\n  " << mp.getMessage()->c_str();

  std::cout << "\n\n";
}