How do I move the pointer to line k of a text file?

[main pendant]

Yeah thats it.

[red pewter]

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[idle bloom]

Do you want to modify the text in the k line or just read the k line from the text file ?

[idle bloom]

If you wanna just ready the k line:

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

int main() {
    std::ifstream file("cos.txt"); 
    if (!file.is_open()) {
        std::cerr << "Error opening file!" << std::endl;
        return 1;
    }

    int k = 5; 
    std::string line;
    int currentLine = 0;

    while (std::getline(file, line)) {
        currentLine++;
        if (currentLine == k) {
            break;
        }
    }
    std::cout<<line;
    file.close();
}

If you wanna modify the k line than you need to rewrite the entire file

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

void writeToLine(const std::string& filename, int lineNumber, const std::string& newContent) {
    std::ifstream fileIn(filename); 
    if (!fileIn.is_open()) {
        std::cerr << "Error opening the file" << std::endl;
        return;
    }

    std::vector<std::string> lines;
    std::string line;
    int currentLine = 0;

    
    while (std::getline(fileIn, line)) {
        currentLine++;
        if (currentLine == lineNumber) {
            lines.push_back(newContent); // Replace the content of the k line
        } else {
            lines.push_back(line); // Keep other lines without change
        }
    }

    fileIn.close();

    std::ofstream fileOut(filename); 
    if (!fileOut.is_open()) {
        std::cerr << "Error opening the file" << std::endl;
        return;
    }

    for (const std::string& l : lines) {
        fileOut << l << '\n';
    }

    fileOut.close();
}

int main() {
    std::string filename = "cos.txt";
    int k= 5; 
    std::string newContent = "Changed text";

    writeToLine(filename, k, newContent);

    return 0;
}

[main pendant]

Okay, I didn't know about the std::getline(file, line) function

I just need to move the pointer to the beginning of any specified line, that is all.

[idle bloom]

Yeah it move you a line that will get you to the start of the line (maybe I'm not understanding you if so feel free to correct me). You wanna write to this line or you wanna open a file and move the pointer to it? Moving just cursor will be done with seekg :

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

int main() {
    
    std::ifstream file("example.txt");
    if (!file) {
        std::cerr << "Unable to open the file.\n";
        return 1;
    }

    
    std::vector<std::streampos> linePositions;

    
    std::streampos position = file.tellg(); 
    std::string line;
    while (std::getline(file, line)) {
        linePositions.push_back(position);
        position = file.tellg(); 
    }

    
    file.close();
    file.open("example.txt");

    
    int lineNumber = 5; 
    if (lineNumber > 0 && lineNumber <= linePositions.size()) {
        file.seekg(linePositions[lineNumber - 1]); // Move to the start of the desired line

        
        std::getline(file, line);
        std::cout << "Line " << lineNumber << ": " << line << "\n";
    } else {
        std::cerr << "Invalid line number.\n";
    }

    file.close();
    return 0;
}

[main pendant]

No like: the pointer will have some location (obviously), but the only way to move it was to move it relative to either itself, the beginning of the document or the end of the document. But I am asking is whether it is possible to move the pointer to the beginning of the k-th line, without reading anything (yet, I can make that myself).

and also using getline(file, line) gives me an error

[idle bloom]

what kind of error ?

[main pendant]

this is all the info you need

[idle bloom]

std::ifstream readEngFin("example.txt");

[main pendant]

should i replace the condition of the while with that?

[idle bloom]

do you have this line with your file?

[main pendant]

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

std::ifstream readEngFin("wordsEngFin.txt");

void pointerMover(int line);

int main() {

  std::string wordEng;
  getline(readEngFin, wordEng, '|');

  std::string wordFin;
  getline(readEngFin, wordFin, '|');

  std::string wordFinInput;
  std::cout << "What is the Finnish word for " << wordEng << "? ";
  std::cin >> wordFinInput;

  if (wordFinInput == wordFin) {
    std::cout << "Good Job!" << std::endl;
  } else {
    std::cout << "No :(" << std::endl;
  };

  return 0; 
}

void pointerMover(int k) {

  int currentLine = 0;

  std::string line; 

  while (std::getline(readEngFin, line)) {
    currentLine++;
    if (currentLine == k) {
      break;
    }
  }
}

[idle bloom]

while (std::getline(readEngFin, line, '\n')) {

try like this

[main pendant]

oke

same error

and i have to go now

[idle bloom]

;compile

[grim verge]

Program Output

What is the Finnish word for ? Good Job!

menium | 40ms | c++ | x86-64 gcc 14.2 | godbolt.org

[idle bloom]

the code compiles like you can see the bot. So I also run it on my own PC and it works, so the problem looks like something with the compiler on your machine.

[main pendant]

visual studio code is at it again

[idle bloom]

ok i see

the error is saying that getline got as params (std::ifstram&, int&) ok it thinks the line arg is int (we can see it isn't)

restart of VS sometimes helps also

[idle bloom]

have a good day and let me know if error went away after the restart

[main pendant]

Im back

[idle bloom]

Do you still have the error ?

[main pendant]

NO

oops

no\

[idle bloom]

ok nice

[idle bloom]

had some time off today would suggest to make few changes

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


void pointerMover(std::ifstream& file, int line);

int main() {
   
    std::ifstream readEngFin("wordsEngFin.txt");
    if (!readEngFin.is_open()) {
        std::cerr << "Error: Could not open the file!" << std::endl;
        return 1;
    }

    
    pointerMover(readEngFin, 1);

    
    std::string wordEng;
    std::getline(readEngFin, wordEng, '|');

    
    std::string wordFin;
    std::getline(readEngFin, wordFin);

    
    std::string wordFinInput;
    std::cout << "What is the Finnish word for " << wordEng << "? ";
    std::cin >> wordFinInput;

    
    if (wordFinInput == wordFin) {
        std::cout << "Good Job!" << std::endl;
    } else {
        std::cout << "No :(" << std::endl;
    }

    readEngFin.close(); 
    return 0;
}

void pointerMover(std::ifstream& file, int k) {
    
    file.clear(); 
    file.seekg(0, std::ios::beg); 

    
    std::string line;
    for (int currentLine = 1; currentLine < k; ++currentLine) {
        if (!std::getline(file, line)) {
            std::cerr << "Error: Line " << k << " does not exist!" << std::endl;
            return;
        }
    }
}

I assumed that the input is
apple|omena
banana|banaani
orange|appelsiini

[main pendant]

!solved