How do I find the line number and line item number in a text file?

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I need to find the line number and position number in a line of a given character in a text file. I did, but I need to read the character not from the beginning, but from the end.
I have a task to find the first point "." in a text file, but in order to search from the end of the file, I have done a search from the beginning of the file, how to do it from the end?
Text file:
One One
....
Two
Three
Four
..

Now I get the following result:
Character position: 8
Line: 2

What I have tried:

Check out my code (I'm looking for the first . in the file):

C++

#include <iostream>
#include <iomanip>
#include <stdio.h>
#include <fstream>
#include <string>

using namespace std;

int Search_position(int& i)
{
    ifstream fin("t.txt"); // file name
    char line;
    int k = 0;
    while ((line = fin.get()) > 0) 
    {
        if (line == '.') 
        {
            k++;
            if (k == 1) 
            {
                return i;
            }
        }
        if (line != '\n')
            i++;
    }
    cout << "No";
    return 0;
}

int Search_line(int& n, int& i)
{
    char line;
    int l = 0;
    ifstream fin("t.txt");
    while ((line = fin.get()) > 0) 
    {
        if (line != '\n')
            l++;
        if (l <= i && line == '\n')
            n++, l++;
    }
    return n;
}
int main()
{
    ifstream fin("t.txt");
    char line[150];
    while (!fin.eof())
    {
        fin.getline(line, sizeof(line));
        cout << line << endl;
    }
    int i = 1;
    int n = 1;
    cout << "\nCharacter position : " << Search_position(i) << endl;
    cout << "\nLine : " << Search_line(n, i) << endl;
    return 0;
}

Posted 9-Apr-22 23:40pm

Jonson123 2022

Updated 10-Apr-22 4:35am

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2 solutions

Solution 1

Technically, you can't - text files are just a stream of characters, some of which are interpreted by software as an "end of line" character.

So finding any specific character position in a file doesn't help you to learn what line it was on, or even where the line it is on actually starts - because lines aren't a fixed length, and can be from zero up to millions of characters long.

The only way is to read the file as lines counting as you go, and then search each of the lines for your character, starting with the last line and working backwards.

Posted 10-Apr-22 0:34am

OriginalGriff

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This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

CPallini · Accepted Answer · 2022-04-10T04:35:00

So you need to report the distance from the end of the file of the last occurrence of the '.'.
Try

C++

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

int main()
{
    ifstream fin("t.txt");
    string line;

    int lines = 0;
    int characters = 0;

    int found_line = 0;
    size_t found_pos = string::npos;

    while (true)
    {
      if ( ! getline(fin, line) ) break;
      auto pos = line.find_last_of('.');
      if ( pos != string::npos)
      {
        found_line = lines;
        found_pos = (characters + pos);
      }
      ++lines;
      characters += line.length();
    }

    if ( found_pos != string::npos)
    {
      found_line = (lines - 1 - found_line); // line no, counting backwards from the bottom of the file
      found_pos = (characters - 1 - found_pos); // pos of the 'first' dot, counting backwards from the end of the file
      cout << "line " << found_line << "\n";
      cout << "pos " << found_pos << "\n";
    }

    return 0;
}

How do I find the line number and line item number in a text file?

2 solutions

Solution 2

Solution 1

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How do I find the line number and line item number in a text file?

2 solutions

Solution 2

Solution 1

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