Why is the file read as empty?

Question

C++ / C#

I have main.cpp and input.txt.
Here is the code:

spoiler

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



using namespace std;

string getResult(vector<string> val) {
    bool flag = true;
    for (int i = 0; i < val.size(); i++) {
        // Iteration
        string current = val[i];

        for (int j = 0; j < current.size(); j++) {
            if (current[j] != ' ') {
                // If first word is uppercase
                if (flag && isupper(current[j]) == 0) {
                    current[j] = toupper(current[j]);
                    val[i] = current;
                }
                flag = false;
            }
        }
        flag = true;
    }

    string result;
    for (int i = 0; i < val.size(); i++)
        result += val[i] + ".";

    return result;
}



int main() {
    ifstream file("input.txt");
    string str;
    string file_contents;

    if (!file.is_open()) {
        cout << "Some problems with file...";
        return -1;
    }



    while (getline(file, str)) {
        file_contents += str;
        file_contents.push_back('\n');
    }

    vector<string> array;

    // split
    istringstream is(str);
    string s;
    while (std::getline(is, s, '.'))
        array.push_back(s);

    cout <<"Current input: "<< str << endl;

    string result = getResult(array);

    cout << "After: " << result << endl;
    return 0;
}

I run it:

$: g++ -o prog main.cpp
$: ./prog

I get:

Current input: 
After:

It feels like the file is empty, but it's not empty. The file is in the same folder as main.cpp. What is the problem?