Goto line number , and edit a string there in file using C++

Tag: c++,file,file-io

I am trying to make a function which gets two parameters one Line_number and 2nd a string. This function will open a File Pre-Populated and skip till Line "Line_number" is reached , get that line and post some other line instead.But it does not work. I have seen other solutions but cant find right solution. Kindly help me with it.

   fstream Inoutput_file;
   void BackPatch(int GotoLineNo, string LineNo)
   {

     for (int i = 1; i <= GotoLineNo; i++)
     {
        char* str = new char[20];
         Inoutput_file.getline(str, 20, '\n');
        if (i == LineNo-1)
        {
            Inoutput_file.seekp(Inoutput_file.tellg());
            Inoutput_file.getline(str, 20, '\n');
            cout << str << endl;                //prints the correct line
            Inoutput_file << "Goto " + str <<endl;  //donot work
            cout << "Goto " + str<<endl;      // Prints correct line
        }

  }
  Inoutput_file.seekp(0);
  Inoutput_file.seekg(0);
}

In main:

  Inoutput_file.open("example.txt");
  BackPatch(3,"Print this to Line 3 instead");
  Inoutput_file.close();

I would Also Like to Mention here that I have opened same File with different instance of "ifstream" to work for rest of my program.

Best How To :

fstream Inoutput_file; void BackPatch(int GotoLineNo, string LineNo) {

 for (int i = 1; i <= GotoLineNo; i++)
 {
    char* str = new char[20];
     Inoutput_file.getline(str, 20, '\n');
    if (i == LineNo-1)
    {
        Inoutput_file.seekp(Inoutput_file.tellg());
        Inoutput_file.getline(str, 20, '\n');
        cout << str << endl;                //prints the correct line
        Inoutput_file << "Goto " + str <<endl;  //Now it will work fine
        cout << "Goto " + str<<endl;      // Prints correct line
    }

}

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