Getting first word of each line in file

Question

I have problem while getting first word of each line in my file. My txt file is:

GB LONDON 1 9 3 0 4 5
D BERLIN 2 5 6 1 4 
E MADRYT 1 2 3 4 5

And I want only to put first word each line of file to array like [GB,D,E]; I tried this:

ifstream plik("galerie.txt");
    
    if(!plik){
        
        
        cout<<"not working";
    }

    
    string city[50];
    int n=0;
    while(plik.eof()){
        plik>>city[n];
    
        n++;
    
    }
    plik.close();

But it gets me every string in line like: GB,LONDON,1,9...

try [`std::getline`](https://en.cppreference.com/w/cpp/string/basic_string/getline) — Alan Birtles, Mar 12 '21 at 15:46
Yes, I tried, but how can I use getline till whitespace because I tried this: getline(plik,city[n],' '); and stillnot working — PolakRobak, Mar 12 '21 at 15:51
`while(plik.eof())` is certainly a typo, but see why the intended `while(!plik.eof())` [is also wrong](https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-i-e-while-stream-eof-cons). — Lukas-T, Mar 12 '21 at 15:55
BTW, your program is ignoring the `if` statement. The file will be read if the input open fails. Maybe you want to `return` an error code instead of continuing. — Thomas Matthews, Mar 12 '21 at 16:53

score 1 · Answer 1 · answered Mar 12 '21 at 16:14

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

int main() {
  std::ifstream plik("galerie.txt");

  if (!plik) {
    std::cerr << "not working";
    return 1;
  }

  std::vector<std::string> city;
  std::string tmp;
  while (std::getline(plik, tmp)) {
    city.push_back(tmp.substr(0, tmp.find_first_of(" ")));
  }
  plik.close();

  for (auto i : city) {
    std::cout << i << '\n';
  }
}

Output:

GB
D
E

Optionally, if you don't want tmp staying in scope longer than it's needed:

  for (std::string tmp; std::getline(plik, tmp);) {
    city.push_back(tmp.substr(0, tmp.find_first_of(" ")));
  }

Lukas-T · Answer 2 · 2021-03-12T16:23:09.633

1

If you only want to keep the first word you have read a single word and ignore the rest of the line. You can use std::istream::ignore to do so.

// read first word of a line
while(plik >> city[n]) 
{
    // skip rest of the line, including the line break
    plik.ignore(std::numeric_limits<std::streamsize>::max(), '\n');

    n++;    
}

edited Mar 12 '21 at 16:23

answered Mar 12 '21 at 16:17

Lukas-T

11,133
3
20
30

Johannes · Answer 3 · 2021-03-14T12:25:48.187

0

! After reading again the question, code is changed and explanation is changed twice!

You are reading word by word without throwing away the words after the first one on each line, and appending it to the string. I guess the best is to read a line and evaluate that, smiliar to Syed has proposed.

ifstream plik("galerie.txt");

if(!plik){
    
    
    cout<<"not working";
}


std::string city;
std:: istringstream streamCity;
std::string line;

streamCity << '[';

while (std::getline(plik, line)) {
    std::string cCode;
    std::istringstream iss(line);        
    iss>>cCode;
    streamCity << cCode << ',';

     n++;

}

streamCity << ']';
plik.close();

edited Mar 14 '21 at 12:25

answered Mar 12 '21 at 16:16

Johannes

11
4

They are not reading character-by-character. – sweenish Mar 12 '21 at 16:19
According to "http://www.cplusplus.com/reference/istream/istream/operator-free/" the line "plik>>city[n];" reads one character and stores it in city[n]. – Johannes Mar 12 '21 at 17:21
1

Of course `std::cin` **can** read into a single character. This code doesn't do that. – sweenish Mar 12 '21 at 17:33
`city[n]` is a `std::string` not a `char`. city is an array of std::string – drescherjm Mar 12 '21 at 20:58
Ok, OMG, you are right! Completely overseen... Sorry. – Johannes Mar 14 '21 at 07:50

Syed Mohib Uddin · Accepted Answer · 2021-03-12T17:49:59.987

-2

You can try this code works fine for me can check on your side. You just need to push in vector instead of output in another file.

#include<iostream>
#include<fstream>
#include <sstream>
#include<string>
using namespace std;

int main()
{
    ifstream fin("input.txt");
    vector<std::string> v;
    string line;
    string word;

    int i;
    int count=0;

    while(!fin.eof())
    {
        getline(fin,line);
        for(i=0;i<line.length();i++)
        {
            if(line[i]==' ')
            {
                break;
            }
            word = word + line[i]
        }
        v.push_back(word);
        word = "";
    }
    for(std::size_t i = 0; i < v.size(); ++i) {
        std::cout << v[i] << "\n";
    }
    return 0;
}

edited Mar 12 '21 at 17:49

answered Mar 12 '21 at 16:09

Syed Mohib Uddin

718
7
16

1

https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-i-e-while-stream-eof-cons – sweenish Mar 12 '21 at 16:17
2

I agree with the above comments, I am unsure why this broken code was accepted as the correct answer. – drescherjm Mar 12 '21 at 16:21
A word in english language is until there is white space so we are checking for it in for loop within while loop if there is a condition satisfied for white space we will break for loop and go to next line. – Syed Mohib Uddin Mar 12 '21 at 16:22
We understand that however the code is broken in the way the two comments above mine point out. – drescherjm Mar 12 '21 at 16:23
Have you ran at your side? – Syed Mohib Uddin Mar 12 '21 at 16:25
1

`cout< – drescherjm Mar 12 '21 at 16:27
Yeah but please try with int once its just a concept no need to copy paste – Syed Mohib Uddin Mar 12 '21 at 16:27
It's an answer to a question, and it doesn't compile. You should not be answering questions with broken code. – sweenish Mar 12 '21 at 16:28
Yeah got it bro @churill thanks for pointing it out fixing it – Syed Mohib Uddin Mar 12 '21 at 16:30
1

Also that sentence _"You just need to push in vector instead of output in another file."_ - OP doesn't have any vector (but maybe should). So it would be nice if you could actually show how to solve this with a vector. If you need some time to fix the answer you can always delete it, [edit], then undelete again. – Lukas-T Mar 12 '21 at 16:32
@churill try now might fix your issue (y) – Syed Mohib Uddin Mar 12 '21 at 16:37
Yeah but I liked your answer also less code more work done (y) – Syed Mohib Uddin Mar 12 '21 at 16:45
2

Now you removed the `getline` and broke the code again. I suggest you test the code before uploading it. You might want to fix the [`while(!fin.eof())`](https://stackoverflow.com/questions/5605125/why-is-iostreameof-inside-a-loop-condition-i-e-while-stream-eof-cons) also. – Lukas-T Mar 12 '21 at 16:45
Specifically, `word` is never used, and `line` is never given a value. – sweenish Mar 12 '21 at 16:55
@churill it should be fine now. – Syed Mohib Uddin Mar 12 '21 at 17:51

Getting first word of each line in file

4 Answers4