Add std::copy_n overload for istreambuf_iterator

["François Dumont" <frs.dumont@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 813 bytes --]

It sounds reasonable to overload std::copy_n for istreambuf_iterator.

     * include/bits/stl_algo.h (copy_n(istreambuf_iterator<>, _Size, 
_OIte)):
     New declaration.
     * include/bits/streambuf_iterator.h (istreambuf_iterator<>): Declare
     std::copy_n for istreambuf_iterator of char types to be friend.
     (std::copy_n(istreambuf_iterator<>, _Size, _OIte)): New overload.
     * include/std/streambuf(basic_streambuf<>): Declare std::copy_n for
     istreambuf_iterator of char types to be friend.
     * testsuite/25_algorithms/copy_n/istreambuf_iterator.cc: New.
     * testsuite/25_algorithms/copy_n/istreambuf_iterator_neg.cc: New.

Tested under Linux x86_64, normal and debug modes.

Ok to commit ?

François


[-- Attachment #2: istreambuf_copy_n.patch --]
[-- Type: text/x-patch, Size: 7290 bytes --]

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 478f012def8..ec651e2cc45 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -771,6 +771,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	     _OutputIterator __result, random_access_iterator_tag)
     { return std::copy(__first, __first + __n, __result); }
 
+  template<typename _CharT, typename _Size, typename _OutputIterator>
+    typename enable_if<__is_char<_CharT>::__value,
+		       _OutputIterator>::type
+    copy_n(istreambuf_iterator<_CharT, char_traits<_CharT> >,
+	   _Size __n, _OutputIterator __result);
+
   /**
    *  @brief Copies the range [first,first+n) into [result,result+n).
    *  @ingroup mutating_algorithms
diff --git a/libstdc++-v3/include/bits/streambuf_iterator.h b/libstdc++-v3/include/bits/streambuf_iterator.h
index 2f4ff494a3a..c682fa91bde 100644
--- a/libstdc++-v3/include/bits/streambuf_iterator.h
+++ b/libstdc++-v3/include/bits/streambuf_iterator.h
@@ -80,6 +80,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	__copy_move_a2(istreambuf_iterator<_CharT2>,
 		       istreambuf_iterator<_CharT2>, _CharT2*);
 
+#if __cplusplus >= 201103L
+      template<typename _CharT2, typename _Size, typename _OutputIterator>
+	friend typename enable_if<__is_char<_CharT2>::__value,
+				  _OutputIterator>::type
+	copy_n(istreambuf_iterator<_CharT2>, _Size, _OutputIterator);
+#endif
+
       template<typename _CharT2>
 	friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
 				    istreambuf_iterator<_CharT2> >::__type
@@ -367,6 +374,50 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return __result;
     }
 
+#if __cplusplus >= 201103L
+  template<typename _CharT, typename _Size, typename _OutputIterator>
+    typename enable_if<__is_char<_CharT>::__value, _OutputIterator>::type
+    copy_n(istreambuf_iterator<_CharT> __it, _Size __n,
+	   _OutputIterator __result)
+    {
+      if (__n == 0)
+	return __result;
+
+      __glibcxx_assert(__n > 0);
+      __glibcxx_requires_cond(!__it._M_at_eof(),
+			      _M_message(__gnu_debug::__msg_inc_istreambuf)
+			      ._M_iterator(__it));
+
+      using traits_type = typename istreambuf_iterator<_CharT>::traits_type;
+      const auto __eof = traits_type::eof();
+
+      auto __sb = __it._M_sbuf;
+      while (__n > 0)
+	{
+	  streamsize __size = __sb->egptr() - __sb->gptr();
+	  if (__size == 0)
+	    {
+	      if (traits_type::eq_int_type(__sb->underflow(), __eof))
+		{
+		  __glibcxx_requires_cond(__n == 0,
+		    _M_message(__gnu_debug::__msg_inc_istreambuf)
+					  ._M_iterator(__it));
+		  break;
+		}
+
+	      __size =  __sb->egptr() - __sb->gptr();
+	    }
+
+	  streamsize __xsize = std::min<streamsize>(__size, __n);
+	  __result = std::copy(__sb->gptr(), __sb->gptr() + __xsize, __result);
+	  __sb->__safe_gbump(__xsize);
+	  __n -= __xsize;
+	}
+
+      return __result;
+    }
+#endif
+
   template<typename _CharT>
     typename __gnu_cxx::__enable_if<__is_char<_CharT>::__value,
 		  		    istreambuf_iterator<_CharT> >::__type
diff --git a/libstdc++-v3/include/std/streambuf b/libstdc++-v3/include/std/streambuf
index d9ca981d704..4f62ebf4d95 100644
--- a/libstdc++-v3/include/std/streambuf
+++ b/libstdc++-v3/include/std/streambuf
@@ -155,6 +155,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
         __copy_move_a2(istreambuf_iterator<_CharT2>,
 		       istreambuf_iterator<_CharT2>, _CharT2*);
 
+#if __cplusplus >= 201103L
+      template<typename _CharT2, typename _Size, typename _OutputIterator>
+	friend typename enable_if<__is_char<_CharT2>::__value,
+				  _OutputIterator>::type
+	copy_n(istreambuf_iterator<_CharT2>, _Size, _OutputIterator);
+#endif
+
       template<typename _CharT2>
         friend typename __gnu_cxx::__enable_if<__is_char<_CharT2>::__value,
 				  istreambuf_iterator<_CharT2> >::__type
diff --git a/libstdc++-v3/testsuite/25_algorithms/copy_n/istreambuf_iterator.cc b/libstdc++-v3/testsuite/25_algorithms/copy_n/istreambuf_iterator.cc
new file mode 100644
index 00000000000..ebd769cf7c0
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/copy_n/istreambuf_iterator.cc
@@ -0,0 +1,59 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run { target c++11 } }
+
+#include <algorithm>
+#include <sstream>
+#include <iterator>
+
+#include <testsuite_hooks.h>
+
+void test01()
+{
+  std::stringstream ss("12345");
+
+  std::string ostr(5, '0');
+  typedef std::istreambuf_iterator<char> istrb_ite;
+  std::copy_n(istrb_ite(ss), 0, ostr.begin());
+  VERIFY( ostr.front() == '0' );
+
+  std::copy_n(istrb_ite(ss), 2, ostr.begin());
+  VERIFY( ostr == "12000" );
+
+  std::copy_n(istrb_ite(ss), 3, ostr.begin() + 2);
+  VERIFY( ostr == "12345" );
+}
+
+void test02()
+{
+  std::stringstream ss("12345");
+
+  std::string ostr(5, '0');
+  typedef std::istreambuf_iterator<char> istrb_ite;
+
+  istrb_ite ibfit(ss);
+  std::copy_n(ibfit, 3, std::copy_n(ibfit, 2, ostr.begin()));
+  VERIFY( ostr == "12345" );
+}
+
+int main()
+{
+  test01();
+  test02();
+  return 0;
+}
diff --git a/libstdc++-v3/testsuite/25_algorithms/copy_n/istreambuf_iterator_neg.cc b/libstdc++-v3/testsuite/25_algorithms/copy_n/istreambuf_iterator_neg.cc
new file mode 100644
index 00000000000..42bc5b64306
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/copy_n/istreambuf_iterator_neg.cc
@@ -0,0 +1,40 @@
+// Copyright (C) 2019 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-do run { target c++11 xfail *-*-* } }
+// { dg-require-debug-mode { } }
+
+#include <algorithm>
+#include <sstream>
+#include <iterator>
+
+#include <testsuite_hooks.h>
+
+void test01()
+{
+  std::stringstream ss("12345");
+
+  std::string ostr(10, '0');
+  typedef std::istreambuf_iterator<char> istrb_ite;
+  std::copy_n(istrb_ite(ss), 10, ostr.begin());
+}
+
+int main()
+{
+  test01();
+  return 0;
+}