How to write an algorithm that finds out in which lines specific word appear (I am using std::map)

I am writing code which calculate how many times each word appears in text ( I DID THIS TASK), but I can't find a way to calculate in which lines these words appeared.

I don't know where to start.

#include "header.h"
int main()
{
     //read the input, keeping track of each word and how often we see it
     std::ifstream in("tekstas.txt"); // input file

    std::string input;
    std::map<std::string, int> counters; // store each word and an associated counter
    std::vector<char>CharVect; // vector that stores symbols i want to replace
    formuojuChar(CharVect); // pushbacking that vector with symbols
     for (unsigned int i = 0; !in.eof(); i++)
    {
        std::getline(in, input);
        std::transform(input.begin(), input.end(), input.begin(), ::tolower); // lowering letters so for example "Mom"= "mom"
        Replace(input,CharVect, ' '); // replace symbols with space
        std::stringstream read(input);
        std::string word;
        while (read >> word)
        {
            ++counters[word];
        }
     }
     std::ofstream out("isvestis.txt");
    std::cout<<"Words that appear more than once in the text: "<<std::endl;
    std::cout<<std::endl;
     for (std::map<std::string, int>::const_iterator it = counters.begin();it != counters.end(); ++it)
        {
            if((it->second)>1)
            {

                std::cout<<"'" <<it->first<<"' " <<"appears "<<it->second <<" times in lines: " ;
                /*
                 ANY IDEAS ?
                 */
                std::cout<<std::endl;

            }
        }
        return 0;

}

I expect output to show me in which .txt file lines that word appears. TY