cppFileIOAdvTellGSeekG

#include <iostream>
#include <fstream>

/*

std::ios::app -- append to file
std::ios::in - open file for input, reading
std::ios::out - open file for output, writeing
std::ios:binary - opens file in binary mode
std::ios::ate - opens file and moves file pointer to END, pr AT ehe End
std::ios::trunc - removes file if exist

*/

// iofile.seekg(iofile.tellg(), std::ios::beg)
int main()
{
    std::fstream iofile;
    iofile.open("test.txt", std::ios::in | std::ios::out); //| std::ios::ate

    //iofile.seekg(0, std::ios::end);

    //std::cout << "Current reading position: " << iofile.tellg() << '\n';

    //iofile.seekg(12, std::ios::beg);

    //std::cout << "First move Current reading position: " << iofile.tellg() << '\n';

    //iofile.seekg(-7, std::ios::cur);

    //std::cout << "Second move Current reading position: " << iofile.tellg() << '\n';
    char buf[100];
    char symbol{};

    while (iofile.get(symbol))
    {
        if (symbol == '#')
        {
            iofile.seekp(((int)iofile.tellg() - 1), std::ios::beg);
            iofile << 't';
            iofile.seekg(iofile.tellg(), std::ios::beg);
        }
    }

    //while (!iofile.eof())
    //{
    //  iofile.getline(buf, 100);
    //  std::cout << buf << '\n';
    //  std::cout << "Current reading position: " << iofile.tellg() << '\n';
    //}

    std::cout << "Current reading position: " << iofile.tellg() << '\n';

    iofile.close();

}