TELLG()

This is used with input file streams, such as ifstream, to determine the current position of the get pointer (read pointer) within a file. The position returned by tellg() is measured in bytes from the beginning of the file, with counting starting at 0, not 1. This means the very first byte in the file corresponds to position 0. tellg() is useful for tracking how much of the file has been read, calculating remaining data, or determining the file size when combined with seekg(). By providing precise information about the read pointer’s location, it enables accurate control for reading and navigating through files.

// Returns the current position of the get (read) pointer
istream::pos_type tellg();

 * istream::pos_type is a type representing positions within a file stream.
 * tellg() is typically used with ifstream (input file stream) or any istream-derived object.

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

int main() {
    ifstream file("example.txt");

    if (!file) {
        cout << "Could not open the file.\n";
        return 0;
    }

    //0 is the beginning of the file
    file.seekg(0, ios::end); // This means pointer is now pointing at the last character of the file

    // Get the current position (which is the size of the file in bytes)
    int size = file.tellg();

    cout << "The file size is: " << size << " bytes\n";

    file.close();
    return 0;
}

FINDING A CHARACTER POSITION

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

int main() {
  ifstream file("sample.txt");
  
  if (!file) {
      cout << "Unable to open file.\n";
  }
  else{
      string line;
      getline(file, line);
      cout << "First line: " << line << "\n";

      int pos = file.tellg();
      cout << "Current read position after reading first line: " << pos << "\n";

      getline(file, line);
      cout << "Second line: " << line << "\n";
      pos = file.tellg();
      cout << "Current read position after reading second line: " << pos << "\n";

      file.close();
  }

  return 0;
}

 * INPUT FILE: sample.txt
    Hello, world!
    This is a test file.
 * OUTPUT:
    First line: Hello, world!
    Current read position after reading first line: 14
    Second line: This is a test file.
    Current read position after reading second line: -1
    
 * This example demonstrates the usage of tellg() in C++, which tells the current 
   position of the get pointer in an input stream.

FINDING CHARACTER POSITION: EXAMPLE 2

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

using namespace std;

int main() {
    // Open the file "log.txt" for reading
    ifstream readFile("log.txt");

    // Check if the file was opened successfully
    if (!readFile.is_open()) {
        // If the file can't be opened, print an error message
        cout << "Failed to open log.txt\n";
    }
    else{
        // Declare a string to hold each line of the file
        string lineContents;


        // Read the file line by line
        while (getline(readFile, lineContents)) {
            // Print the current line read from the file
            cout << "Line: " << lineContents << "\n";

            // Get the current read position in the file
            int pos = readFile.tellg();
            
            // If the position is valid, print it
            if (pos != -1) {
                cout << "Position after read: " << pos << "\n";
            } else {
                // If position is -1, it means the end of the file was reached
                cout << "End of file reached\n";
            }
        }

        // Close the file after reading
        readFile.close();
    }
    
    return 0; // Return 0 to indicate successful execution
}

 * INPUT FILE: log.txt
    Start Process
    Loading Modules
    Initialization Complete
    
 * OUTPUT:
    Line: Start Process
    Position after read: 14
    Line: Loading Modules
    Position after read: 30
    Line: Initialization Complete
    End of file reached