Injecting string to 'cin'

Question

I have a function that reads user input from std::cin, and I want to write a unittest that inserts some strings into std::cin, such that later extraction from std::cin will

Answer 1

cin.putback() is guaranteed to work with at most one character, so you can't putback a whole string. Use a stream that wraps cin and allows arbitrary putback() sequence length. I think Boost.Iostream have something similar, and if it doesn't then it might be helpful to implement such a wrapper.

Answer 2

Instead of screwing around with cin, you can have your program accept a general std::istream&. When running normally, just pass it cin. During a unit test, pass it an I/O stream of your own creation.

Answer 3

If you really, really want to use std::cin, try this:

int main() {
  using namespace std;
  streambuf *backup;
  istringstream oss("testdata");
  backup = cin.rdbuf();
  cin.rdbuf(oss.rdbuf());
  string str;
  cin >> str;
  cout << "read " << str;    
}

You can restore std::cin's streambuf when you are done from backup. I don't guarantee the portability of this ;P