How can I find and replace a line of data in a text file c++

Question

I am trying to find and replace a line of data in a text file in c++. But I honestly have no idea where to start.

I was thinking of using replaceNumber.open(\"

Answer 1

You can use std::stringstream to convert the string read from the file to an integer and use std::ofstream with std::ofstream::trunc to overwrite the file.

#include 
#include 
#include 
#include 
#include 
#include 

int main()
{

    std::ifstream ifs("test.txt");
    std::string line;
    int num, other_num;
    if(std::getline(ifs,line))
    {
            std::stringstream ss;
            ss << line;
            ss >> num;
    }
    else
    {
            std::cerr << "Error reading line from file" << std::endl;
            return 1;
    }

    std::cout << "Enter a number to subtract from " << num << std::endl;
    std::cin >> other_num;

    int diff = num-other_num;
    ifs.close();

    //std::ofstream::trunc tells the OS to overwrite the file
    std::ofstream ofs("test.txt",std::ofstream::trunc); 

    ofs << diff << std::endl;
    ofs.close();

    return 0;
}