c++11 - c++ pass string as refrence in header and cpp -

how pass string reference in constructor in header , cpp using cin line in text file. execute command prompt: program < test.txt

text.txt

aaa bbb ccc 

main.cpp

include "read.h" include <iostream> include <string>  using namespace std;  int main() {  string output;  read read(line);  while (getline(cin, line)) {     read.run();     ...     ... } 

read.cpp

include "read.h" include <iostream>  using namespace std;  read::read(string& input) : currentline(input) {    }  void read::run() {     cout << "currentline:" << currentline << "\r\n";         } 

read.h

class read{ public:     std::string currentline;      parser(std::string& s);      void advance(); } 

when execute program in cmd: program < test.txt currentline not have value

string output;  read read(line);  while (getline(cin, line)) {     read.run();     ...     ... } 

you set read.currentline input (in constructor) currentline isn't reference, copied, resulting in empty string. make currentline reference too. beware of dangling references though.