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libstdc++: make negative count safe with std::for_each_n

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The Library Working Group have approved a change to std::for_each_n that
requires it to handle negative N gracefully, which we were not doing for
random access iterators.

	* include/bits/stl_algo.h (for_each_n): Handle negative count.
	* testsuite/25_algorithms/for_each/for_each_n_debug.cc: New test.

From-SVN: r277932
This commit is contained in:
Jonathan Wakely 2019-11-07 23:10:45 +00:00 • committed by Jonathan Wakely
parent b77cc8aa09
commit 3a99fd4dbb
3 changed files with 51 additions and 0 deletions
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5
libstdc++-v3/ChangeLog
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@ -1,3 +1,8 @@
2019-11-07 Jonathan Wakely <jwakely@redhat.com>
* include/bits/stl_algo.h (for_each_n): Handle negative count.
* testsuite/25_algorithms/for_each/for_each_n_debug.cc: New test.
2019-11-07 Jason Merrill <jason@redhat.com>
* libsupc++/compare: Remove strong_equality and weak_equality.

2
libstdc++-v3/include/bits/stl_algo.h
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@ -4011,6 +4011,8 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
using _Cat = typename iterator_traits<_InputIterator>::iterator_category;
if constexpr (is_base_of_v<random_access_iterator_tag, _Cat>)
{
if (__n2 <= 0)
return __first;
auto __last = __first + __n2;
std::for_each(__first, __last, std::move(__f));
return __last;

44
libstdc++-v3/testsuite/25_algorithms/for_each/for_each_n_debug.cc Normal file
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@ -0,0 +1,44 @@
// 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-options "-std=gnu++17" }
// { dg-do run { target c++17 } }
#include <algorithm>
#include <debug/vector>
#include <debug/list>
void
test01()
{
__gnu_debug::vector<int> v{1, 2, 3};
std::for_each_n(v.begin(), -2, [](int){});
}
void
test02()
{
__gnu_debug::list<int> l{1, 2, 3};
std::for_each_n(l.begin(), -2, [](int){});
}
int
main()
{
test01();
test02();
}