cin的数据类型是什么

C++标准 §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标头声明将对象与关联的对象 中声明的函数提供的标准C流 (27.9.2),并包括使用这些 物体。

您还可以查看gcc 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

cin 是一个 对象 的 istream 班