Reading words from a text file: weird behaviour

Question

I'm running the following program

#include <iostream>
#include <fstream>
#include <string>
#include <vector>

using namespace std;

int main(int argc, char *argv[])
{
    ifstream input_file(argv[1]);
    vector<string> words;
    string line;

    while(getline(input_file, line))
    {
        cout << line << endl;
        words.push_back(line);
    }
    input_file.close();

    cout << "First and last word: " << words[0] << " " << words.back() << endl;

    return 0;
}

using the following text file as an input

permission
copper
operation
cop
rationale
rest

and I get the following output in terminal

permission
copper
operation
cop
rationale
rest

 rest and last word: permission

Why is the last word words.back() printed at the beginning of the line while erasing some of the text?

https://stackoverflow.com/questions/45956271/stdgetline-reads-carriage-return-r-into-the-string-how-to-avoid-that — Renat, Aug 04 '20 at 14:05
`ifstream input_file(argv[1]);` -- Basically, you told a fib to the file I/O library and stated the file is a text file, when it isn't a text file. Once you did that, expect all sorts of weird things to happen. — PaulMcKenzie, Aug 04 '20 at 14:07
@PaulMcKenzie It _is_ a text file, and telling the lib that it's a binary file won't fix this issue. — Asteroids With Wings, Aug 04 '20 at 14:45
What I am saying is that as far as the I/O library is concerned, the file is not what would be considered a text file due to the line endings. It essentially is a "binary" file. — PaulMcKenzie, Aug 04 '20 at 14:50

Asteroids With Wings · Accepted Answer · 2020-08-04T14:37:33.440

Because your file has Windows line-endings ("\r\n") and you're on Linux or Mac (which doesn't translate these into "\n").

std::getline is only trimming the '\n's for you. So, \r is left at the end of each of your strings; in many consoles, '\r' moves the write cursor to the start of the line. Then, the " " << words.back() part overwrites the already-written "First and last word: " << words[0] part.

Example:

First word is permission␍
Last word is rest␍

(Note the ␍ control character at the end of each word!)

┌───────────────────┬──────────────────────────────────────┐
│                   │  ⭭⭭⭭⭭⭭                               │
│ Write "First"     │  First                               │
│                   │       ꕯ                              │
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┤
│                   │       ⭭⭭⭭⭭                           │
│ Write " and"      │  First·and                           │
│                   │           ꕯ                          │
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┤
│                   │           ⭭⭭⭭⭭⭭                      │
│ Write " last"     │  First·and·last                      │
│                   │                ꕯ                     │
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┤
│                   │                ⭭⭭⭭⭭⭭⭭                │
│ Write " word:"    │  First·and·last·word:                │
│                   │                      ꕯ               │
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┤
│                   │                      ⭭⭭⭭⭭⭭⭭⭭⭭⭭⭭⭭␍    │
│ Write first word  │  First·and·last·word:·permission     │
│                   │  ꕯ                                   │
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┤
│                   │  ⭭                                   │
│ Write " "         │  ·irst·and·last·word:·permission     │
│                   │   ꕯ                                  │
├┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┼┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┤
│                   │   ⭭⭭⭭⭭␍                              │
│ Write last word   │  ·rest·and·last·word:·permission     │
│                   │  ꕯ                                   │
└───────────────────┴──────────────────────────────────────┘

Solution

You can strip this from the end of each line yourself, or preprocess the file externally.

Reading words from a text file: weird behaviour

1 Answers1

Example:

Solution