libc++ iostream: Clean up standard I/O stream object creation in preparation for conditionalizing streams

[ed]

Summary

Interleave the code for narrow and wide character streams. This makes it more obvious that the two pieces of code are identical. Furthermore, it makes it easier to conditionally compile support for certain streams, as less #ifdef blocks are needed.

[jroelofs]

I'm going to have to defer to @mclow.lists on this one... I'm not sure whether the state_types have to be contiguous or not.

[ed]

In D8342#140948, @jroelofs wrote:

I'm going to have to defer to @mclow.lists on this one... I'm not sure whether the state_types have to be contiguous or not.

I just looked through include/__std_stream and it doesn't seem to be the case that they need to be contiguous.

The address of the mbstate_t is stored in the __st_ member. A reference to it gets passed on to codecvt objects. The codecvt code in src/locale.cpp passes on the addresses to wcrtomb_l() and friends. It looks like we never do any pointer arithmetic on them.

[mclow.lists]

How about we do this in two steps:

1. Move the code around w/o any functionality change.

[ i.e, Interleave the code for narrow and wide character streams. This makes it more obvious that the two pieces of code are identical. ]

2. Get rid (maybe) of the mbstates array - though I don't really see the motivation for that.

[ed]

In D8342#141422, @mclow.lists wrote:

2. Get rid (maybe) of the mbstates array - though I don't really see the motivation for that.

The reason why I removed the array and replaced it by separate mbstates is that once the change for making std::cin and std::cout optional hits the tree, the array will only be used partially. You could add some #ifdefs to reduce the size of the array and use different indexing based on whether std::cin/std::cout should be present, but that makes things even worse.

Let me split this change up even further.

[ed]

In D8342#141435, @ed wrote:

Let me split this change up even further.

Done!

libcxx/trunk/src/iostream.cpp

 #include "__std_stream"
 #include "string"
 #include "new"
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 static mbstate_t state_types[6] = {};
 
+_ALIGNAS_TYPE (istream)  _LIBCPP_FUNC_VIS char cin [sizeof(istream)];
 _ALIGNAS_TYPE (__stdinbuf<char> ) static char __cin [sizeof(__stdinbuf <char>)];
-_ALIGNAS_TYPE (__stdoutbuf<char>) static char __cout[sizeof(__stdoutbuf<char>)];
-_ALIGNAS_TYPE (__stdoutbuf<char>) static char __cerr[sizeof(__stdoutbuf<char>)];
+_ALIGNAS_TYPE (wistream) _LIBCPP_FUNC_VIS char wcin [sizeof(wistream)];
 _ALIGNAS_TYPE (__stdinbuf<wchar_t> ) static char __wcin [sizeof(__stdinbuf <wchar_t>)];
-_ALIGNAS_TYPE (__stdoutbuf<wchar_t>) static char __wcout[sizeof(__stdoutbuf<wchar_t>)];
-_ALIGNAS_TYPE (__stdoutbuf<wchar_t>) static char __wcerr[sizeof(__stdoutbuf<wchar_t>)];
 
-_ALIGNAS_TYPE (istream)  _LIBCPP_FUNC_VIS char cin [sizeof(istream)];
 _ALIGNAS_TYPE (ostream)  _LIBCPP_FUNC_VIS char cout[sizeof(ostream)];
-_ALIGNAS_TYPE (ostream)  _LIBCPP_FUNC_VIS char cerr[sizeof(ostream)];
-_ALIGNAS_TYPE (ostream)  _LIBCPP_FUNC_VIS char clog[sizeof(ostream)];
-_ALIGNAS_TYPE (wistream) _LIBCPP_FUNC_VIS char wcin [sizeof(wistream)];
+_ALIGNAS_TYPE (__stdoutbuf<char>) static char __cout[sizeof(__stdoutbuf<char>)];
 _ALIGNAS_TYPE (wostream) _LIBCPP_FUNC_VIS char wcout[sizeof(wostream)];
+_ALIGNAS_TYPE (__stdoutbuf<wchar_t>) static char __wcout[sizeof(__stdoutbuf<wchar_t>)];
+
+_ALIGNAS_TYPE (ostream)  _LIBCPP_FUNC_VIS char cerr[sizeof(ostream)];
+_ALIGNAS_TYPE (__stdoutbuf<char>) static char __cerr[sizeof(__stdoutbuf<char>)];
 _ALIGNAS_TYPE (wostream) _LIBCPP_FUNC_VIS char wcerr[sizeof(wostream)];
+_ALIGNAS_TYPE (__stdoutbuf<wchar_t>) static char __wcerr[sizeof(__stdoutbuf<wchar_t>)];
+
+_ALIGNAS_TYPE (ostream)  _LIBCPP_FUNC_VIS char clog[sizeof(ostream)];
 _ALIGNAS_TYPE (wostream) _LIBCPP_FUNC_VIS char wclog[sizeof(wostream)];
 
 ios_base::Init __start_std_streams;
 
 ios_base::Init::Init()
 {
     istream* cin_ptr  = ::new(cin)  istream(::new(__cin)  __stdinbuf <char>(stdin, state_types+0) );
+    wistream* wcin_ptr  = ::new(wcin)  wistream(::new(__wcin)  __stdinbuf <wchar_t>(stdin, state_types+3) );
     ostream* cout_ptr = ::new(cout) ostream(::new(__cout) __stdoutbuf<char>(stdout, state_types+1));
+    wostream* wcout_ptr = ::new(wcout) wostream(::new(__wcout) __stdoutbuf<wchar_t>(stdout, state_types+4));
     ostream* cerr_ptr = ::new(cerr) ostream(::new(__cerr) __stdoutbuf<char>(stderr, state_types+2));
                         ::new(clog) ostream(cerr_ptr->rdbuf());
-    cin_ptr->tie(cout_ptr);
-    _VSTD::unitbuf(*cerr_ptr);
-    cerr_ptr->tie(cout_ptr);
-
-    wistream* wcin_ptr  = ::new(wcin)  wistream(::new(__wcin)  __stdinbuf <wchar_t>(stdin, state_types+3) );
-    wostream* wcout_ptr = ::new(wcout) wostream(::new(__wcout) __stdoutbuf<wchar_t>(stdout, state_types+4));
     wostream* wcerr_ptr = ::new(wcerr) wostream(::new(__wcerr) __stdoutbuf<wchar_t>(stderr, state_types+5));
                           ::new(wclog) wostream(wcerr_ptr->rdbuf());
+
+    cin_ptr->tie(cout_ptr);
     wcin_ptr->tie(wcout_ptr);
+    _VSTD::unitbuf(*cerr_ptr);
     _VSTD::unitbuf(*wcerr_ptr);
+    cerr_ptr->tie(cout_ptr);
     wcerr_ptr->tie(wcout_ptr);
 }
 
 ios_base::Init::~Init()
 {
     ostream* cout_ptr = reinterpret_cast<ostream*>(cout);
-    ostream* clog_ptr = reinterpret_cast<ostream*>(clog);
+    wostream* wcout_ptr = reinterpret_cast<wostream*>(wcout);
     cout_ptr->flush();
-    clog_ptr->flush();
+    wcout_ptr->flush();
 
-    wostream* wcout_ptr = reinterpret_cast<wostream*>(wcout);
+    ostream* clog_ptr = reinterpret_cast<ostream*>(clog);
     wostream* wclog_ptr = reinterpret_cast<wostream*>(wclog);
-    wcout_ptr->flush();
+    clog_ptr->flush();
     wclog_ptr->flush();
 }
 
 _LIBCPP_END_NAMESPACE_STD