Writing Pool objects to a file and reading them back - C++ File Stream

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Description

Writing Pool objects to a file and reading them back

Demo Code

#include  <fstream>
#include  <iostream>
#include  <string>
#include  <vector>
#include  <iomanip>

using  std::string;

class Pool//from w  w  w  .  java  2 s  . c  o  m
{
private:
  double length {1.0};
  double width {1.0};
  double height {1.0};

public:
  // Constructors
  Pool(double lv, double wv, double hv) : length {lv}, width {wv}, height {hv} {}

  Pool() = default;                                          // Default constructor

  Pool(const Pool& pool)                                     // Copy constructor
    : length {pool.length}, width {pool.width}, height {pool.height} {}

  double volume() const                                   // Calculate the volume
  {
    return length*width*height;
  }

  friend std::ostream& operator<<(std::ostream& stream, const Pool& pool);
  friend std::istream& operator>>(std::istream& in, Pool& pool);
};

// Stream insertion operator for Pool objects
inline std::ostream&  operator<<(std::ostream& out, const  Pool&  pool)
{
  return out << std::setw(10) << pool.length << ' '
    << std::setw(10) << pool.width << ' '
    << std::setw(10) << pool.height << '\n';
}

// Stream extraction operation for Pool objects
inline std::istream&  operator>>(std::istream& in, Pool&  pool)
{
  return in >> pool.length >> pool.width >> pool.height;
}

int main()
try
{
  std::vector<Pool> pools {Pool {1.0, 2.0, 3.0}, Pool {2.0, 2.0, 3.0},
    Pool {3.0, 2.0, 2.0}, Pool {4.0, 2.0, 3.0},
    Pool {1.0, 4.0, 3.0}, Pool {2.0, 2.0, 4.0}};

  const string filename {"D:\\Example_Data\\pools.txt"};
  std::ofstream out {filename};

  if (!out)
    throw std::ios::failure {string {"Failed to open output file "} +filename};

  for (auto& pool : pools)
    out << pool;                        // Write a Pool object
  out.close();                         // Close the input stream

  std::cout << pools.size() << " Pool objects written to the file." << std::endl;

  std::ifstream in {filename};         // Create a file input stream
  if (!in)                              // Make sure it's valid
    throw std::ios::failure {string("Failed to open input file ") + filename};

  std::cout << "Reading objects from the file.\n";
  std::vector<Pool> newPools;
  Pool newPool;
  while (true)
  {
    in >> newPool;
    if (!in) break;
    newPools.push_back(newPool);
  }
  in.close();                          // Close the input stream
  std::cout << newPools.size() << " objects read from the file:\n";
  for (auto& pool : newPools)
  std::cout << pool;
}
catch (std::exception& ex)
{
  std::cout << typeid(ex).name() << ": " << ex.what() << std::endl;
}

Result


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