CODEWITHSUNDEEP
c++
R3troRice
R3troRice

Reputation: 29

How to read data from a file then convert the data to an int and store them in a vector

I am trying to read in data from a text file, convert its contents into an integer, and finally store the integer values into a vector. However, I'm having an issue where the conversion skips the last number in the .txt file and seems to add a random value at the beginning of the vector when it goes to print it out.

For example, my test.txt file has the following values (Note: All of the values are put on its own line):

23
57
81
19 
26
45
38
63
99
4

Here is my main.cpp:

#include <iostream>
#include <fstream>
#include <vector>
using namespace std;

int main() 
{ 
    vector<int> myIntArray;
    string line;
    ifstream fileName("test.txt");

    for(int number; getline(fileName, line, '\n'); number = stoi(line))
    {
        myIntArray.push_back(number);
        cout << "Reading in number from the file: " << number << endl;
    }
}

Once I run the program this is the output that I get:

Reading in number from the file: 28156
Reading in number from the file: 23
Reading in number from the file: 57
Reading in number from the file: 81
Reading in number from the file: 19
Reading in number from the file: 26
Reading in number from the file: 45
Reading in number from the file: 38
Reading in number from the file: 63
Reading in number from the file: 99

I'm not sure where that first number (28156) came from or why it skips the last number (4) in my test.txt file but this is the problem that I am having with my code.

Upvotes: 1

Views: 733

Answers (3)

user4640261
user4640261

Reputation:

You can also construct the vector using an input iterator:

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

int main() {
  using namespace std;

  ifstream f("test.txt");
  vector<int> myIntArray(istream_iterator<int>(f), {});

  for(auto i: myIntArray) {
    cout << "Reading in number from the file: " << i << endl;
  }
}

Upvotes: 3

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

You can simplify your loop like this:

for(int number; filename >> number;)
{
    myIntArray.push_back(number);
    cout << "Reading in number from the file: " << number << endl;
}

Upvotes: 3

MikeCAT
MikeCAT

Reputation: 75062

The 3rd part of for loop (number = stoi(line) in this case) is executed after executing the loop body.

Therefore, the 28156 is an indeterminate value of uninitialized non-static local variable and the last 4 is converted and discarded.

You have to do conversion before using number like this:

    for(int number; getline(fileName, line, '\n'); )
    {
        number = stoi(line);
        myIntArray.push_back(number);
        cout << "Reading in number from the file: " << number << endl;
    }

Upvotes: 3

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