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As discussed on cfe-dev [1], use the using_if_exists Clang attribute when the compiler supports it. This makes it easier to port libc++ on top of new platforms that don't fully support the C Standard library. Previously, libc++ would fail to build when trying to import a missing declaration in a <cXXXX> header. With the attribute, the declaration will simply not be imported into namespace std, and hence it won't be available for libc++ to use. In many cases, the declarations were *not* actually required for libc++ to work (they were only surfaced for users to use them as std::XXXX), so not importing them into namespace std is acceptable. The same thing could be achieved by conscious usage of `#ifdef` along with platform detection, however that quickly creates a maintenance problem as libc++ is ported to new platforms. Furthermore, this problem is exacerbated when mixed with vendor internal-only platforms, which can lead to difficulties maintaining a downstream fork of the library. For the time being, we only use the using_if_exists attribute when it is supported. At some point in the future, we will start removing #ifdef paths that are unnecessary when the attribute is supported, and folks who need those #ifdef paths will be required to use a compiler that supports the attribute. [1]: http://lists.llvm.org/pipermail/cfe-dev/2020-June/066038.html Differential Revision: https://reviews.llvm.org/D90257
48 lines
926 B
C++
48 lines
926 B
C++
// -*- C++ -*-
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//===--------------------------- cstdarg ----------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP_CSTDARG
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#define _LIBCPP_CSTDARG
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/*
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cstdarg synopsis
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Macros:
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type va_arg(va_list ap, type);
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void va_copy(va_list dest, va_list src); // C99
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void va_end(va_list ap);
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void va_start(va_list ap, parmN);
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namespace std
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{
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Types:
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va_list
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} // std
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*/
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#include <__config>
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#include <stdarg.h>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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#pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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using ::va_list _LIBCPP_USING_IF_EXISTS;
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP_CSTDARG
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