std::getline read the last string twice

Question

Test file wrote like

   Sat Aug 10 22:03:09 2019
   Test completed

First i used in.eof(), but someone told me do never use thoes in.eof().

enter code here
#include <fstream>
#include <iostream>
#include <string>

int main() {
  //test.txt is a test file. 
  std::ifstream in("test.txt");

if (!in.is_open()) {
   std::cout << "file not found" << std::endl;
return 0;
}

std::string s;
while (in) {
getline(in, s);
std::cout << s << std::endl;
  }

  return 0;
}

I'd expect the result like

   Sat Aug 10 22:03:09 2019
   Test completed

But the result is

   Sat Aug 10 22:03:09 2019
   Test completed
   Test completed

Answer 1

The standard way to do what you want is

for (std::string s; std::getline(in, s);)

The issue may be related with the new line symbol (\n) at the end of the file.

Answer 2

The problem is with this part of the code, just after the last successful read:

while (in) {          // succeeds
    std::getline(in, s);   // fails (EOF), and s is unchanged

This is exactly equivalent to Why is iostream::eof inside a loop condition (i.e. while (!stream.eof())) considered wrong?.

The fix is to make the getline() result part of the condition:

while(std::getline(in, s)) {

Answer 3

Loop while getline is successfull and not while the istream is valid.

while (getline(in, s)) {
  std::cout << s << std::endl;
  }