Directly capturing cin without a variable - C++ [closed]

Question

More of a curiosity question than anything else, but is it actually possible to pass whatever goes through cin to a function without having to waste a variable?

Answer 1

You can easily define a wrapper function to do this.

template<class T>
T get(std::istream& is){
  T result;
  is >> result;
  return result;
}

Any decent compiler will use NRVO to eliminate the copy.

You can use it like this

f(get<int>(std::cin));

Make sure not to use it multiple times in one statement though. The order of the stream operations is unspecified if you do something like this.

f(get<int>(std::cin),get<int>(std::cin));

You could get the two ints in either order.

Answer 2

cin is just a stream, it doesn't have any magic. You can use the other stream methods to do whatever you want.

Check out http://www.cplusplus.com/reference/iostream/

Answer 3

The answer to your question is negative. In order to input something through a stream, you will have to "waste" a variable. You cannot pass the input data directly to a function without an intermediate variable.

Answer 4

Sure:

f(*std::istream_iterator<T>(std::cin));

That’s probably not simpler than using a variable, though, and is undefined behavior if the stream fails to provide a T.