C++ numbers in a file to a array

Question

Im working on a program to take a input file, sort it and print the output. These input files will have 10 , 100, 1000 or 100000 lines which each have a number per line.

Right now, my code only works for the first 10 lines.

the main part is

int array[10];
int size;
size = sizeof array/sizeof(int);

and

if(file.is_open())
    {

        for(int i = 0; i < size ; ++i)
        {
            file >> array[i];
        }
    }

to read the lines of the file into the array.

How can i change this to take variable lengths of file line sizes and read it into a array.

#include<iostream>

#include<string>
#include<fstream>
#include<vector>
#include<ctime>
using namespace std;


void insertion_sort(int x[],int length)
{
  int key,i;
  for(int j=1;j<length;j++)
  {
     key=x[j];
     i=j-1;
     while(x[i]>key && i>=0)
     {
               x[i+1]=x[i];
         i--;
     }
     x[i+1]=key;
  }
}


int main()
{

int array[10];
int size;
size = sizeof array/sizeof(int);
int x;


char name[256];

string sort, order, dup;


cout << "enter a file\n";
cin >> name;

ofstream ofile;
ifstream file(name);


if(file.is_open())
    {

        for(int i = 0; i < size ; ++i)
        {
            file >> array[i];
        }
    }
else{
            cout << "file doesnt exist";
            return 1;
        }
size = sizeof array/sizeof(int);
cout << "enter a sort method - type insertion_sort or merge_sort or quick_sort or counting_sort\n";
cin >> sort;

cout << "Type 'dec' for non decreasing or 'inc' for increasing order\n";
cin >> order;

cout << "Type yes or no to remove duplicates\n";
cin >> dup;


if (sort ==  "insertion_sort")

{

insertion_sort(array,size);
cout << "\ninsertion sort";
}


if (order == "dec"  )
    for(int i=0;i<size/2;i++)
                swap(array[i],array[size-i-1]);

if(dup == "yes")
    {


    int i, j;


    int NewLength = 1;

    for(i=1; i< size; i++){

       for(j=0; j< NewLength ; j++)
       {

          if(array[i] == array[j])
          break;
       }



      if (j==NewLength )
          array[NewLength++] = array[i];
    }

    }




cout<<endl<<"sorted "<<endl;
      for(x=0;x<size;x++)
      {
           cout<<array[x]<<endl;
      }




    return 0;
    }

you must have considered std::vector, right?

Zac Wrangler
– Zac Wrangler

2013-10-13 04:57:44 +00:00
Commented Oct 13, 2013 at 4:57 — Zac Wrangler
– Zac Wrangler, Commented Oct 13, 2013 at 4:57

Zac Howland · Accepted Answer · 2013-10-13 05:00:17Z

2

For starters, you should be using std::vector and std::string instead of static arrays. Once you switch your code to use a vector, pulling in a file of integer data is as simple as:

std::ifstream fin("myfile.dat");
std::vector<int> myVec;
std::copy(std::istream_iterator<int>(fin), std::istream_iterator<int>(), std::back_inserter(myVec));

Which also makes the output fairly simple:

std::ofstream fout("myNewFile.dat");
std::copy(myVec.begin(), myVec.end(), std::ostream_iterator<int>(fout, " "));

answered Oct 13, 2013 at 5:00

Zac Howland

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5 Comments

Jerry Coffin Over a year ago

...or even simpler, like: std::vector<int> myVec{std::istream_iterator<int>(fin), std::istream_iterator<int>()};

johnsyweb Over a year ago

Or... std::multiset<int> container{ std::istream_iterator<int>(fin), std::istream_iterator<int>() }; Sorting: sorted!

Zac Howland Over a year ago

@Johnsyweb Given that this appears to be a homework assignment, I doubt it would be acceptable for him to use a set to sort it automatically. But outside of academia, yes.

johnsyweb Over a year ago

@ZacHowland: True enough :-)

Jerry Coffin Over a year ago

@Johnsyweb: Just keep in mind that using an std::multiset will generally trade off quite a bit of performance for the sake of a minor improvement in simplicity. For only 100000 items, it's probably fine, but if you have to deal with a lot of input, it may not be such a good idea.

Simon · Accepted Answer · 2013-10-13 05:01:26Z

1

Something like

std::vector<int> vec;
int x;
while (file >> x)
{
    vec.push_back(x);
}

might simplify your life.

answered Oct 13, 2013 at 5:01

Simon

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4 Comments

Zac Howland Over a year ago

Why write your own custom loop when you have one already made for you?

Simon Over a year ago

@ZacHowland I upvoted your answer! I left this one because the op is a beginner and that might be easier to grasp.

Carey Gregory Over a year ago

@ZacHowland Which was really a better answer than giving him the solution outright.

Zac Howland Over a year ago

@CareyGregory His assignment appears to deal with an insertion sort, which none of us has addressed, so it appears safe to say that we haven't "given him the solution".

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