replace line in a file C++ -

i'm trying find way replace line, containing string, in file new line.

if string not present in file, append file.

can give sample code?

edit : there anyway if line need replace @ end of file?

although recognize not smartest way it, following code reads demo.txt line line , searches word cactus replace oranges while writing output secondary file named result.txt.

don't worry, saved work you. read comment:

#include <iostream> #include <fstream> #include <string> #include <algorithm>  using namespace std;   int main() {   string search_string = "cactus";   string replace_string = "oranges";   string inbuf;   fstream input_file("demo.txt", ios::in);   ofstream output_file("result.txt");    while (!input_file.eof())   {       getline(input_file, inbuf);        int spot = inbuf.find(search_string);       if(spot >= 0)       {          string tmpstring = inbuf.substr(0,spot);          tmpstring += replace_string;          tmpstring += inbuf.substr(spot+search_string.length(), inbuf.length());          inbuf = tmpstring;       }        output_file << inbuf << endl;   }    //todo: delete demo.txt , rename result.txt demo.txt   // achieve replace effect. }