libstdc++: Fix default mode of new basic_stringstream constructor [PR 97719]

libstdc++-v3/ChangeLog:

	PR libstdc++/97719
	* include/std/sstream (basic_stringstream(string_type&&, openmode)):
	Fix default argument.
	* testsuite/27_io/basic_stringstream/cons/char/97719.cc: New test.

2 files changed, 41 insertions, 1 deletions

diff --git a/libstdc++-v3/include/std/sstream b/libstdc++-v3/include/std/sstream
index 33a00486606..8acf1eb259a 100644
--- a/libstdc++-v3/include/std/sstream
+++ b/libstdc++-v3/include/std/sstream
@@ -976,7 +976,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
 
       explicit
       basic_stringstream(__string_type&& __str,
-	                 ios_base::openmode __mode = ios_base::out
+	                 ios_base::openmode __mode = ios_base::in
 						     | ios_base::out)
       : __iostream_type(), _M_stringbuf(std::move(__str), __mode)
       { this->init(std::__addressof(_M_stringbuf)); }
diff --git a/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/char/97719.cc b/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/char/97719.cc
new file mode 100644
index 00000000000..fa523a803b6
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_stringstream/cons/char/97719.cc
@@ -0,0 +1,40 @@
+// Copyright (C) 2020 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-options "-std=gnu++2a" }
+// { dg-do run { target c++2a } }
+
+#include <sstream>
+#include <iterator>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  // PR libstdc++/97719
+  std::string str = "a";
+  std::stringstream s(std::move(str));
+  std::istreambuf_iterator<char> i(s);
+  VERIFY( i != std::istreambuf_iterator<char>() );
+  VERIFY( *i == 'a' );
+}
+
+int
+main()
+{
+  test01();
+}