getline() infinite loop while reading from file

Question

I'm trying to take text from file 1 and justify the content to file 2 by filling spaces with a random seed.

Everything seems to be working but I can't reach the end of the input file. The program get stuck in the loop when reading a certain line.

File 1 for reading

https://pastebin.com/raw/rRhcz3Tw

File 2 after pasting file 1

https://pastebin.com/raw/uRrJVdy3

I've read about flags problem and i'm wondering if that may be the case?

My code:

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

using namespace std;

unsigned int plusLongueChaine(ifstream& file);
void ajoutEspace(string& ligne, const unsigned int maxChaine);

int main()
{
    srand(time(0));

    // Création des instances de lecture et écriture
    ifstream fin("ip.txt", ios::in);
    ofstream fout("ip2.txt", ios::out);

    // Si le fichier n'est pas trouvé
    if (!fin.is_open()) {
        cerr << "Ouverture du fichier impossible." << endl;
        return 1; // Prototype dans cstdlib
    }

    // 1 - Trouver la plus longue ligne dans le fichier
    const unsigned int maxChaine = plusLongueChaine(fin);
    string ligneAEcrire;

    fin.clear();
    fin.seekg(0, ios::beg);
    

    // 2 - Boucle principale
    while (getline(fin, ligneAEcrire)) {
        if (ligneAEcrire.empty()) {
            fout << "\n" << endl;
            continue;
        }

        if (ligneAEcrire.size() < maxChaine)
            ajoutEspace(ligneAEcrire, maxChaine);


        fout << ligneAEcrire << endl;
    }

    cout << maxChaine; // 84


    return 0;
}

void ajoutEspace(string& ligne, const unsigned int maxChaine) {
    unsigned int position = 0;

    while (ligne.size() < maxChaine) {
        position = ligne.find(' ', position);

        if (position < ligne.size() && position != string::npos) {
            if (rand() & 1)
                ligne.insert(position, "_");

            position = ligne.find_first_not_of(' ', position);
            cout << position << endl; 
        }
        else {
            position = 0;
        }
    }

}

unsigned int plusLongueChaine(ifstream& file) {
    string ligne;
    unsigned int longueurChaine = 0;

    while (getline(file, ligne)) {
        if (ligne.size() > longueurChaine)
            longueurChaine = ligne.size();
    }

    return longueurChaine;
}

Answer 1

Your problem is in void ajoutEspace(string& ligne) which enters an infinite loop. You do not need to pass maxChaine as a parameter. You are passing a reference to a std::string line. All you want to do is find the ' ' in the line and convert to '_' in a varying manner. Simply use position = ligne.find(' ', position) and then update position += 1; (and another +1 if the space is randomly replaced with '_' ) before the next call, eg

void ajoutEspace(string& ligne)
{
    size_t position = 0;

    while ((position = ligne.find(' ', position)) != std::string::npos) {
            if (rand() & 1) {
                ligne.insert(position, "_");
                position += 1;
            }
            position += 1;
    }
}

( note: the change to size_t from unsigned int . You should be receiving warnings about your tests always being true when you compare, eg position:= string::npos due to the limitation of the range of unsigned int compared to size_t )

You are using find , so control your loop based on the return from find() , eg

    while ((position = ligne.find(' ', position)) != std::string::npos) {

That way you ensure you break the loop the first time a space is not found.

Example Output File

First ten lines of the modified file:

$ head ip2.txt
1. Introduction


1.1. Motivation


Le Protocole_ Internet est conçu pour_ supporter l'intercommunication_ de systèmes_
informatiques sur une base_ de_ réseau_ par_ commutation de paquets. Un_ tel_ système_ est
appelé "catenet"_ [1]. Le rôle du protocole_ Internet est_ la_ transmission de blocs de
données,_ appelés_ datagrammes,_ d'une_ source_ vers une destination, la_ source_ et la

( note: your line fout << "\n" << endl; inserts two newlines for every empty line in the original file)

Make the changes and let me know if you have further questions.