C++ Stop while loop at the end of the line (enter Key)

Question

Task: Create program to read given text file and print into another text file all lines containing given substring. Reading from files should be carried out line per line.

My code:

#include <bits/stdc++.h>
#include <iostream>
#include <fstream>
using namespace std;

int main(){
    fstream file; // required for input file further processing
    ofstream outputFile; 
    string word1, word2, t, q, inputFileName;

    string keyWord = "morning";
    string enterKey = "\n";
  
    inputFileName = "inputFile.txt";
    file.open(inputFileName.c_str());  // opening the EXISTING INPUT file

    outputFile.open("outputFile.txt"); // CREATION of OUTPUT file

    // extracting words from the INPUT file
    while (file >> word1){
        if(word1 == keyWord) {
            while(file >> word2 && word2 != enterKey){
                // printing the extracted words to the OUTPUT file
                outputFile << word2 << " ";
            }
        }
        
    }

    outputFile.close();
  
    return 0;
}

1st problem: outputFile contains the whole text, in other words while loop is not stopping at the place whre enter is pressed.

2nd problem: Processing of string is not starting from the beginning of the text.

Try `std::getline` the `>>` operator discards all whitespace including newlines — Alan Birtles, Sep 11 '21 at 06:05
Quick suggestion - If you are using UNIX like systems (eg Linux, MacOS), you can use the command 'cat inputFile.txt | grep morning > outputFile.txt' to get the desired results. — Abdus Khazi, Sep 11 '21 at 06:32
Alan Birtles, Abdus Khazi, thank you for the suggestions, guys! — Robert Kovalauskis, Sep 11 '21 at 08:59

score 1 · Accepted Answer · edited Sep 11 '21 at 09:16

The issue is that you are reading word by word. A stream uses "\n" as a token seperater. Hence it is ignored during word reading. Use getline standard function to get a line.

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>

using namespace std;

int main(){
    string inputFileName = "inputFile.txt";
    string outputFileName = "outputFile.txt";

    fstream inputfile;
    ofstream outputFile; 

    inputfile.open(inputFileName.c_str());
    outputFile.open(outputFileName.c_str());

    string keyWord = "morning";
    string line;
    while (std::getline(file, line)) {
        // Processing from the beginning of each line.
        if(line.find(keyWord) != string::npos)
            outputFile << line << "\n";
    }
}

Got the idea from the answer in Read file line by line using ifstream in C++

C++ Stop while loop at the end of the line (enter Key)

1 Answers1