Read integers from file - line by line

Question

How can I read integers from a file to the array of integers in c++? So that, for example, this file\'s content:

23
31
41
23

would become:<

Answer 1

std::ifstream file_handler(file_name);

// use a std::vector to store your items.  It handles memory allocation automatically.
std::vector<int> arr;
int number;

while (file_handler>>number) {
  arr.push_back(number);

  // ignore anything else on the line
  file_handler.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}

Answer 2

You can just use file >> number for this. It just knows what to do with spaces and linebreaks.

For variable-length array, consider using std::vector.

This code will populate a vector with all numbers from a file.

int number;
vector<int> numbers;
while (file >> number)
    numbers.push_back(number);

Answer 3

Here's one way to do it:

#include <fstream>
#include <iostream>
#include <iterator>

int main()
{
    std::ifstream file("c:\\temp\\testinput.txt");
    std::vector<int> list;

    std::istream_iterator<int> eos, it(file);

    std::copy(it, eos, std::back_inserter(list));

    std::for_each(std::begin(list), std::end(list), [](int i)
    {
        std::cout << "val: " << i << "\n";
    });
    system("PAUSE");
    return 0;
}

Answer 4

don't use array use vector.

#include <vector>
#include <iterator>
#include <fstream>

int main()
{
    std::ifstream      file("FileName");
    std::vector<int>   arr(std::istream_iterator<int>(file), 
                           (std::istream_iterator<int>()));
                       // ^^^ Note extra paren needed here.
}