C++ Reading from text file data type as struct and store data in vectors of lists

Question

I have a large data in text file in form:

1 0.933 2 0.865 3 0.919 4 0.726 
2 0.854 3 0.906 4 0.726 
2 0.882 5 0.853 4 0.897
.
. etc

every integer number follows with its float value. I want to read this file line by line, and store each line in list. I know how to do that using array of linked lists, but, I couldn't fix the memory leak. I read that it is better to use STL instead. Example:

    list 1=  1 0.933 2 0.865 3 0.919 4 0.726 
    list 2=  2 0.854 3 0.906 4 0.726 
    list 3=  2 0.882 5 0.853 4 0.897
.
.

I'm not sure if the (vectors of lists) is similar to the (array of linked lists). I have tried different ways but all my attempts failed.

#include "stdafx.h"
#include <vector>
#include <list>
#include <iostream>
#include <map>
#include <sstream>
#include <iterator>
#include <fstream>

struct MyData{
    int Item;
    float Prob;
};
std::istream& operator>>(std::istream &is, MyData&d)
{
    return is >> d.Item >> d.Prob;
}


int main()
{

    std::ifstream in("DataF.txt");
    std::string line;
    int i = 0;
    while (std::getline(in, line)) {
            typedef std::istream_iterator<MyData> MyDataIstrIt;
            std::stringstream ss(line);             
        std::vector< std::list< MyData> >  data3{ MyDataIstrIt(ss), MyDataIstrIt() }; //  here I couldn't fix the  extractor definition for the vectors of lists

// another attempt
/*std::vector<MyData> data{ MyDataIstrIt(ss), MyDataIstrIt() };
  std::vector< std::list< MyData> > data2;
  data2.push_back(std::vector<MyData>()); // I read this is important for memory leak
  data2.push_back(data);*/
 // data2[i].push_back(data);
 // ++i;



    }
    system("PAUSE");
    return 0;
}

I would use std::vector<std::unordered_map<int, float>> for this if the order of each line's items isn't mandatory. If it is required to be sorted I would use std::vector<std::map<int, float>>. If the original exact order is required, then use std::vector<std::vector<MyData>>> or a similar construct. The first two maintains the int as an index, which has its benefits. — WhozCraig
– WhozCraig, Commented Feb 22, 2014 at 3:40

Brandon · Accepted Answer · 2014-02-22 03:48:55Z

3

There are better ways to do it of course but for the sake of showing you how to use a list or read into one and then place that into a vector..

#include <vector>
#include <list>
#include <iostream>
#include <map>
#include <sstream>
#include <iterator>
#include <fstream>

struct MyData
{
    int Item;
    float Prob;
};

std::istream& operator>>(std::istream &is, MyData&d)
{
    return is >> d.Item >> d.Prob;
}

int main()
{
    std::string line;
    std::vector<std::list<MyData>> data;

    std::ifstream in("DataF.txt"); //don't forget to check `if (in.is_open())`

    while(std::getline(in, line))
    {
        std::stringstream ss(line);
        std::list<MyData> inner;
        MyData info;

        while(ss >> info)
        {
            inner.push_back(info);
        }

        data.push_back(inner);
    }

    for (auto &list : data)
    {
        for (auto &mdata : list)
        {
            std::cout<<mdata.Item<<"   "<<mdata.Prob<<"\n";
        }
    }
}

edited Feb 22, 2014 at 3:48

answered Feb 22, 2014 at 3:39

Brandon

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1 Comment

Sandy Over a year ago

Thank you, when you said "There are better ways to do it" do you mean more efficient? if it's yes can you tell what the best way since I have very large file, and before processing i want to save the data file in the format (store each line inside container, ex. the first line in list, the second line in second list and so on)

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