Question

Here is the code:

// pointers to structures
#include <iostream>
#include <string>
#include <sstream>
using namespace std;

struct movies_t {
  string title;
  int year;
};

int main ()
{
  string mystr;

  movies_t amovie;
  movies_t * pmovie;
  pmovie = &amovie;

  cout << "Enter title: ";
  getline (cin, pmovie->title);
  cout << "Enter year: ";
  getline (cin, mystr);
  (stringstream) mystr >> pmovie->year;

  cout << "\nYou have entered:\n";
  cout << pmovie->title;
  cout << " (" << pmovie->year << ")\n";

  return 0;
}

Taken from http://www.cplusplus.com/doc/tutorial/structures/. I was hoping I could get clarification on a few things.

1. What is getline and how does it work? I tried looking up the documentation, but I’m still having trouble understanding. Also, what exactly is cin and how is it being used with getline?

2. If I understand correctly, pmovie->title essentially says that pmovie points to the member title of the object amovie? If so, and it’s not already clear from the explanation to #1, how does getline (cin, pmovie->title) work?

3. Now this (stringstream) mystr >> pmovie->year is giving me the most trouble. What is a stringstream, and are we using it like we would cast a double as a int, for example?

Thank you all!

Answer 1

What is getline and how does it work? I tried looking up the documentation, but I’m still having trouble understanding. Also, what exactly is cin and how is it being used with getline?

The getline function reads a line from a istream. The cin stream refers to your standard input stream, the one you would normally get input from. It is being passed to getline to tell it which input stream to get a line from.

If I understand correctly, pmovie->title essentially says that pmovie points to the member title of the object amovie? If so, and it’s not already clear from the explanation to #1, how does getline (cin, pmovie->title) work?

The getline functions reads a line from cin and stores it in pmovie->title which is passed by reference.

Now this (stringstream) mystr >> pmovie->year is giving me the most trouble. What is a stringstream, and are we using it like we would cast a double as a int, for example?

A stringstream is a class that makes a string act like a stream. This is kind of confusing syntax (C-style cast) that makes it a bit harder to understand what it is happening. Basically, a temporary stringstream is created and initialized with the contents of mystr. A stringstream, when initialized with a string, gives you a stream from which you can read those contents. The >> operator reads from an output stream, in this case, into pmovie->year, which is again passed by reference.

By the way, it seems to me like you’re trying to understand unusually complex and confusing uses without yet understanding the more basic uses of these objects. That’s a very hard way to learn.