Reading input from file and populating array to store data for later use

Question

I'm trying to make multiple arrays of maximum size 10 that hold the contents of an input file. Suppose the file is formatted like:

1 3 2 4 0 5 8 -3
3 1 4 6 0 3
4 83 2 12 1 3
4 30 4 -2

Where each line cannot exceed more than 10 integers.

void read_input(ifstream &file)
{
    vector<array<int, 10> > main_array;

    while(!(file.eof()))
    {
        int idx = 0;
        string values;
        array<int, 10> part_array;

        getline(file, values);
        istringstream inStream;
        inStream.str(values);

        while((inStream >> part_array[idx++]).good() == true);
        main_array.push_back(part_array);

        file.ignore();
    }

    for(auto it = main_array.begin(); it != main_array.end(); it++)
    {
        for(auto& s: *it)
        {
            cout << s <<  " ";
        }
        cout << "\n";
    }
}

This gives me the output:

1 3 2 4 0 5 8 -3 0 6164240
1 4 6 0 3 5 8 -3 0 6164240
83 2 12 1 3 5 8 -3 0 6164240
30 4 -2 1 3 5 8 -3 0 6164240

Which is clearly wrong. I know this may have to do with me iterating over array elements that aren't initialized, but how can I avoid this error? Just as a note, it is essentially that I use arrays to hold the values at each line in the file. That is, one array must handle the integers in the first line; another in the second line...

while(!(file.eof())) is broken - move string values; before and change to while (getline(file, values)).... — Tony Delroy
– Tony Delroy, Commented Dec 5, 2013 at 9:41
I'm still missing the first value of each row after the first row. Any ideas why this is? — user3064097
– user3064097, Commented Dec 5, 2013 at 9:46

Daniel · Accepted Answer · 2013-12-05 09:52:54Z

2

Use this if you find it useful,

void readData(ifstream &inf)
{
    string str;
    vector<vector<int>> intArr;

    while (getline(inf, str))
    {
        stringstream ss(str);
        int i;
        vector<int> a;
        while (ss >> i)
        {
            a.push_back(i);
        }
        intArr.push_back(a);
    }
}

You shouldn't use eof() to check end of file.

answered Dec 5, 2013 at 9:52

Daniel

2,1831 gold badge14 silver badges14 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

kamilm · Accepted Answer · 2013-12-05 10:23:12Z

2

You can use

 vector<vector<int> > main_array;

instead of an array - then just read items from input and push them (push_back) into the "inner" vector - this way you won't have uninitialized array elements at the end in case when data row is shorter than 10 elements.

Full solution may look like this (I've kept some parts of your original code for consistency):

using namespace std;

void read_input(ifstream &file)
{
    vector<vector<int> > main_array;

    string line;    //buffer for single line read from file 
    // reading part
    while(getline(file, line))
    {       
        stringstream inStream(line);
        vector<int> row;    //single row buffer
        int val = 0;
        while(inStream >> val)
        {
            row.push_back(val);
        }       
        main_array.push_back(row);
    }   

    //display part
    for(auto it = main_array.begin(), end = main_array.end(); it != end; ++it)
    {
        for(auto& s: *it)
        {
            cout << s <<  " ";
        }
        cout << "\n";
    }
}

edited Dec 5, 2013 at 10:23

answered Dec 5, 2013 at 9:38

kamilm

1401 silver badge9 bronze badges

1 Comment

Fszczemton Over a year ago

If you're using a non C++11 standard compiler don't forget about that space between brackets (just like kamilm put it there). If you're C++11 you can drop it.

UmNyobe · Accepted Answer · 2013-12-05 09:47:31Z

1

std::array is a container that encapsulates constant size arrays., so by declaring with array<int, 10> there are already 10 integers in the array. You need to use vector instead, and change your loop

 while((inStream >> part_array[idx++]).good() == true);

to

 bool good = true;
 while(idx <10 ) {
     int v;
     if(!(inStream >> v).good() ) break;
     idx++;
     part_array.push_back(v); //now a vector
 }

edited Dec 5, 2013 at 9:47

answered Dec 5, 2013 at 9:41

UmNyobe

23.1k10 gold badges64 silver badges90 bronze badges

Comments

doctorlove · Accepted Answer · 2013-12-05 10:00:08Z

0

You have used an array with 10 elements but you know there may be fewer than ten items. It would be better to use a vector, and push_back what you have.

Aside from that, there are a variety of potential problems with the code. If you send it a bad ifstream it gets stuck in a loop.

while(!(file.eof())) is asking for trouble.

Next, file.ignore(); then ignores the first items of each line. If you change to use a vector of vectors as people have said, use while(getline(file, values)) instead of using the eof check and remove the ignore it should work.

edited Dec 5, 2013 at 10:00

answered Dec 5, 2013 at 9:39

doctorlove

19.4k3 gold badges49 silver badges65 bronze badges

Comments

Vlad from Moscow · Accepted Answer · 2013-12-05 09:41:47Z

-1

Change this line

array<int, 10> part_array;

to

array<int, 10> part_array = {};

answered Dec 5, 2013 at 9:41

Vlad from Moscow

313k27 gold badges204 silver badges358 bronze badges

1 Comment

user3064097 Over a year ago

I seem to be missing the first value of each row after the first row. Can you spot why that is?

Collectives™ on Stack Overflow

Reading input from file and populating array to store data for later use

5 Answers 5

Comments

1 Comment

Comments

Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

1 Comment

Comments

Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related