PR libstdc++/81338 correctly manage string capacity

Backport from mainline
2017-07-10  Jonathan Wakely  <jwakely@redhat.com>

	PR libstdc++/81338
	* include/bits/basic_string.h [_GLIBCXX_USE_CXX11_ABI] (basic_string):
	Declare basic_stringbuf to be a friend.
	* include/bits/sstream.tcc (basic_stringbuf::overflow)
	[_GLIBCXX_USE_CXX11_ABI]: Use unused capacity before reallocating.
	* include/std/sstream (basic_stringbuf::__xfer_bufptrs): Update string
	length to buffer length.
	* testsuite/27_io/basic_stringstream/assign/81338.cc: New.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-7-branch@251652 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 40 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/27_io/basic_stringstream/assign/81338.cc b/libstdc++-v3/testsuite/27_io/basic_stringstream/assign/81338.cc
new file mode 100644
index 000000000000..30370c0dd42b
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/basic_stringstream/assign/81338.cc
@@ -0,0 +1,40 @@
+// Copyright (C) 2017 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 <sstream>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::stringstream ss;
+  for (int i = 0; i < 100; ++i)
+  {
+    ss << 'a';
+    VERIFY( static_cast<bool>(ss) );
+    VERIFY( ss.str() == "a" );
+    ss = std::stringstream();
+  }
+}
+
+int
+main()
+{
+  test01();
+}