PR libstdc++/83511 add default argument to basic_string_view::substr

	PR libstdc++/83511
	* include/std/string_view (basic_string_view::substr): Add default
	argument to first parameter.
	* include/experimental/string_view (basic_string_view::substr):
	Likewise.
	* testsuite/21_strings/basic_string_view/operations/substr/char/
	83511.cc: New test.
	* testsuite/21_strings/basic_string_view/operations/substr/wchar_t/
	83511.cc: New test.
	* testsuite/experimental/string_view/operations/substr/char/83511.cc:
	New test.
	* testsuite/experimental/string_view/operations/substr/wchar_t/83511.cc:
	New test.

From-SVN: r266568

7 files changed, 168 insertions, 2 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index dc989bc744f..6d781b5593b 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,19 @@
+2018-11-28  Jonathan Wakely  <jwakely@redhat.com>
+
+	PR libstdc++/83511
+	* include/std/string_view (basic_string_view::substr): Add default
+	argument to first parameter.
+	* include/experimental/string_view (basic_string_view::substr):
+	Likewise.
+	* testsuite/21_strings/basic_string_view/operations/substr/char/
+	83511.cc: New test.
+	* testsuite/21_strings/basic_string_view/operations/substr/wchar_t/
+	83511.cc: New test.
+	* testsuite/experimental/string_view/operations/substr/char/83511.cc:
+	New test.
+	* testsuite/experimental/string_view/operations/substr/wchar_t/83511.cc:
+	New test.
+
 2018-11-28  Edward Smith-Rowland  <3dw4rd@verizon.net>
 
 	Implement uniform container erasure for C++20.
diff --git a/libstdc++-v3/include/experimental/string_view b/libstdc++-v3/include/experimental/string_view
index b3bc1a9fb4f..b45463f89a3 100644
--- a/libstdc++-v3/include/experimental/string_view
+++ b/libstdc++-v3/include/experimental/string_view
@@ -273,7 +273,7 @@ inline namespace fundamentals_v1
       // [string.view.ops], string operations:
 
       constexpr basic_string_view
-      substr(size_type __pos, size_type __n=npos) const
+      substr(size_type __pos = 0, size_type __n = npos) const
       {
 	return __pos <= this->_M_len
 	     ? basic_string_view{this->_M_str + __pos,
diff --git a/libstdc++-v3/include/std/string_view b/libstdc++-v3/include/std/string_view
index dc2478d8d0e..b4d9cf56a9d 100644
--- a/libstdc++-v3/include/std/string_view
+++ b/libstdc++-v3/include/std/string_view
@@ -243,7 +243,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 
       constexpr basic_string_view
-      substr(size_type __pos, size_type __n = npos) const noexcept(false)
+      substr(size_type __pos = 0, size_type __n = npos) const noexcept(false)
       {
 	__pos = _M_check(__pos, "basic_string_view::substr");
 	const size_type __rlen = std::min(__n, _M_len - __pos);
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/substr/char/83511.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/substr/char/83511.cc
new file mode 100644
index 00000000000..60899130b83
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/substr/char/83511.cc
@@ -0,0 +1,38 @@
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++17 } }
+
+// Copyright (C) 2018 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/>.
+
+// basic_string_view::substr
+
+#include <string_view>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  const std::string_view s = "abcdef";
+  VERIFY( s.substr() == s );
+  VERIFY( std::string_view{}.substr().empty() );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/substr/wchar_t/83511.cc b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/substr/wchar_t/83511.cc
new file mode 100644
index 00000000000..478194d138f
--- /dev/null
+++ b/libstdc++-v3/testsuite/21_strings/basic_string_view/operations/substr/wchar_t/83511.cc
@@ -0,0 +1,38 @@
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++17 } }
+
+// Copyright (C) 2018 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/>.
+
+// basic_string_view::substr
+
+#include <string_view>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  const std::wstring_view s = L"abcdef";
+  VERIFY( s.substr() == s );
+  VERIFY( std::wstring_view{}.substr().empty() );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/experimental/string_view/operations/substr/char/83511.cc b/libstdc++-v3/testsuite/experimental/string_view/operations/substr/char/83511.cc
new file mode 100644
index 00000000000..84acc2cd8a2
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/string_view/operations/substr/char/83511.cc
@@ -0,0 +1,37 @@
+// { dg-do run { target c++14 } }
+
+// Copyright (C) 2018 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/>.
+
+// experimental::basic_string_view::substr
+
+#include <experimental/string_view>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  const std::experimental::string_view s = "abcdef";
+  VERIFY( s.substr() == s );
+  VERIFY( std::experimental::string_view{}.substr().empty() );
+}
+
+int
+main()
+{
+  test01();
+}
diff --git a/libstdc++-v3/testsuite/experimental/string_view/operations/substr/wchar_t/83511.cc b/libstdc++-v3/testsuite/experimental/string_view/operations/substr/wchar_t/83511.cc
new file mode 100644
index 00000000000..d52addf5ead
--- /dev/null
+++ b/libstdc++-v3/testsuite/experimental/string_view/operations/substr/wchar_t/83511.cc
@@ -0,0 +1,37 @@
+// { dg-do run { target c++14 } }
+
+// Copyright (C) 2018 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/>.
+
+// experimental::basic_string_view::substr
+
+#include <experimental/string_view>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  const std::experimental::wstring_view s = L"abcdef";
+  VERIFY( s.substr() == s );
+  VERIFY( std::experimental::wstring_view{}.substr().empty() );
+}
+
+int
+main()
+{
+  test01();
+}