Question

I want to save the content of different files to a vector:
Vector(0) = Content File1
Vector(1) = Content File2
…

Later on I need to read out from each index of this vector line by line (getline):

getline(Vector(0), string myString)

As I read on different sites, I can’t use vector<istream> myVector.

So how can I solve?

Answer 1

It depends on the size of the data you want to manipulate. My two samples has been tested.

You can use a class which handles some raw pointers

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

class file_vector 
{
public:
  file_vector()
  {}

  virtual ~file_vector()
  {
    for( std::vector< std::ifstream* >::iterator it = m_file_streams.begin(); it != m_file_streams.begin(); it++)
    {
      std::ifstream * p_stream = *it;
      delete p_stream;
    }
  }

  void append_file(const std::string& file_name)
  {
    std::ifstream * p_stream = new std::ifstream( file_name.c_str() );
    if(p_stream->is_open())
      m_file_streams.push_back(p_stream);
    else
      delete p_stream;
  }

  void reset()
  {
    for( std::vector< std::ifstream* >::iterator it = m_file_streams.begin(); it != m_file_streams.end(); it++)
    {
      std::ifstream * p_stream = *it;
      p_stream->seekg(0,p_stream->beg);
    }
  }

  size_t size()
  {
    return m_file_streams.size();
  }

  std::ifstream & get(size_t index)
  {
    return * m_file_streams.at(index); // Using at because of index check
  }

  std::ifstream & operator [] (size_t index)
  {
    return get(index);
  }

private:
  std::vector< std::ifstream* > m_file_streams;
};


int main()
{
  file_vector files_content;
  files_content.append_file("file1.txt");
  files_content.append_file("file2.txt");
  files_content.append_file("file3.txt");

  for(size_t i = 0; i < files_content.size(); i++)
  {
    std::string current_line;
    while(std::getline(files_content[i],current_line))
      std::cout << current_line << std::endl;
  }

  files_content.reset(); // To make getline usable again


  return 0;
}

Or a std::vector< std::vector< std::string > >. That’s a basic solution for small files but it works.

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

typedef std::vector< std::string > string_vec;
typedef std::vector< std::string >::iterator string_it;

typedef std::vector< string_vec> file_vec;
typedef std::vector< string_vec >::iterator file_it;

int main()
{
  string_vec file_names;
  file_names.push_back("file1.txt");
  file_names.push_back("file2.txt");
  file_names.push_back("file3.txt");

  file_vec files_content;
  string_vec empty_file_content;

  for(string_it file_name = file_names.begin(); file_name != file_names.end(); file_name++)
  {
    std::ifstream input_stream( file_name->c_str() );
    files_content.push_back(empty_file_content);

    if(input_stream.is_open())
    {
      string_vec & current_file_content = files_content[ files_content.size() - 1 ];
      std::string current_line;
      while(std::getline(input_stream, current_line))
        current_file_content.push_back(current_line);
    }
  }

  // Some stuff

    // Reading the content later on
  for(file_it file = files_content.begin(); file != files_content.end(); file++)
  {
    for(string_it line = file->begin(); line != file->end(); line++)
    {
      std::cout << *line << std::endl;
    }
  }

  return 0;
}