What is datatype of cin

user_8957908 0
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I would like to know what cin exactly is. I mean a function or class....

I am sure it not a function as the way we use cin is very different from the a function is called.

That leaves options like class or object or something else.

What is it exactly?

cin c++
2 Answers

C++ Standard §27.4.1 [iostream.objects.overview]

#include <ios>
#include <streambuf>
#include <istream>
#include <ostream>

namespace std {
  extern istream cin;
  extern ostream cout;
  extern ostream cerr;
  extern ostream clog;
  extern wistream wcin;
  extern wostream wcout;
  extern wostream wcerr;
  extern wostream wclog;
}

p1 The header declares objects that associate objects with the standard C streams provided for by the functions declared in (27.9.2), and includes all the headers necessary to use these objects.

You may also take a look at gcc's implementation on github:

namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  // Standard stream objects.
  // NB: Iff <iostream> is included, these definitions become wonky.
  typedef char fake_istream[sizeof(istream)]
  __attribute__ ((aligned(__alignof__(istream))));
  typedef char fake_ostream[sizeof(ostream)]
  __attribute__ ((aligned(__alignof__(ostream))));
  fake_istream cin;
  fake_ostream cout;
  fake_ostream cerr;
  fake_ostream clog;

#ifdef _GLIBCXX_USE_WCHAR_T
  typedef char fake_wistream[sizeof(wistream)]
  __attribute__ ((aligned(__alignof__(wistream))));
  typedef char fake_wostream[sizeof(wostream)]
  __attribute__ ((aligned(__alignof__(wostream))));
  fake_wistream wcin;
  fake_wostream wcout;
  fake_wostream wcerr;
  fake_wostream wclog;
#endif

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
user_2752210

cin is an object of the istream class

user_71217420
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