How to read a file into vector in C++?

Question

I need to read from a .data or .txt file containing a new float number on each line into a vector.

I have searched far and wide and applied numerous different methods but every time I get the same result, of a Main.size() of 0 and an error saying "Vector Subscript out of Range", so evidently the vector is just not reading anything into the file.

Note: the file is both in the folder and also included in the VS project.

Anyway, here's my code:

#include <iostream> #include <fstream> #include <sstream> #include <vector> #include <string>  using namespace std;  int main() {      vector<double> Main;     int count;     string lineData;     double tmp;      ifstream myfile ("test.data", ios::in);      double number;        myfile >> count;     for(int i = 0; i < count; i++) {         myfile >> tmp;         Main.push_back(tmp);         cout << count;     }      cout << "Numbers:\n";     cout << Main.size();     for (int i=0; i=((Main.size())-1); i++) {         cout << Main[i] << '\n';     }      cin.get();      return 0; } 

The result I get is always simply:

Numbers: 0 

Answer 1

Your loop is wrong:

for (int i=0; i=((Main.size())-1); i++) { 

Try this:

for (int i=0; i < Main.size(); i++) { 

Also, a more idiomatic way of reading numbers into a vector and writing them to stdout is something along these lines:

#include <iostream> #include <iterator> #include <fstream> #include <vector> #include <algorithm> // for std::copy  int main() {   std::ifstream is("numbers.txt");   std::istream_iterator<double> start(is), end;   std::vector<double> numbers(start, end);   std::cout << "Read " << numbers.size() << " numbers" << std::endl;    // print the numbers to stdout   std::cout << "numbers read in:\n";   std::copy(numbers.begin(), numbers.end(),              std::ostream_iterator<double>(std::cout, " "));   std::cout << std::endl;  } 

although you should check the status of the ifstream for read errors.