0b6a182c
 Hu Chunming
添加无鉴权注册和注销
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// (C) Copyright Edward Diener 2011-2015,2019
// Use, modification and distribution are subject to the Boost Software License,
// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt).
#if !defined(BOOST_VMD_IS_EMPTY_HPP)
#define BOOST_VMD_IS_EMPTY_HPP
#include <boost/vmd/detail/setup.hpp>
#if BOOST_PP_VARIADICS
#include <boost/preprocessor/punctuation/is_begin_parens.hpp>
#include <boost/vmd/detail/is_empty.hpp>
/*
The succeeding comments in this file are in doxygen format.
*/
/** \file
*/
/** \def BOOST_VMD_IS_EMPTY(...)
\brief Tests whether its input is empty or not.
The macro checks to see if the input is empty or not.
It returns 1 if the input is empty, else returns 0.
The macro is a variadic macro taking any input.
For the VC++8 compiler (VS2005) the macro takes a single parameter of input to check.
For all levels of C++ prior to C++20 the macro is not perfect,
and can not be so. The problem area is if the input to be
checked is a function-like macro name, in which case either
a compiler error can result or a false result can occur.
For C++20, with its support for the new __VA_OPT__ preprocessor
construct, the macro will always work correctly no matter what
the variadic input, and is therefore 100% reliable.
This macro is a replacement, using variadic macro support,
for the undocumented macro BOOST_PP_IS_EMPTY in the Boost
PP library. The code is taken from a posting by Paul Mensonides
of a variadic version for BOOST_PP_IS_EMPTY, and changed
in order to also support VC++. The code for the C++20
implementation of the macro, using the __VA_OPT__ preprocessor
construct, is the author's own and reuses code added to the
Boost preprocessor library by this author.
... = variadic input, for VC++8 this must be a single parameter
returns = 1 if the input is empty, 0 if it is not
It is recommended to append BOOST_PP_EMPTY() to whatever input
is being tested in order to avoid possible warning messages
from some compilers about no parameters being passed to the macro
when the input is truly empty.
*/
#if BOOST_VMD_MSVC_V8
#define BOOST_VMD_IS_EMPTY(sequence) \
BOOST_VMD_DETAIL_IS_EMPTY_IIF \
( \
BOOST_PP_IS_BEGIN_PARENS \
( \
sequence \
) \
) \
( \
BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \
BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \
) \
(sequence) \
/**/
#else
# if defined(__cplusplus) && __cplusplus > 201703L
#include <boost/preprocessor/variadic/has_opt.hpp>
#include <boost/preprocessor/facilities/is_empty.hpp>
#define BOOST_VMD_IS_EMPTY(...) \
BOOST_VMD_DETAIL_IS_EMPTY_IIF \
( \
BOOST_PP_VARIADIC_HAS_OPT() \
) \
( \
BOOST_PP_IS_EMPTY_OPT, \
BOOST_VMD_IS_EMPTY_NO_OPT \
) \
(__VA_ARGS__) \
/**/
# else
#define BOOST_VMD_IS_EMPTY(...) \
BOOST_VMD_IS_EMPTY_NO_OPT(__VA_ARGS__) \
/**/
# endif
#define BOOST_VMD_IS_EMPTY_NO_OPT(...) \
BOOST_VMD_DETAIL_IS_EMPTY_IIF \
( \
BOOST_PP_IS_BEGIN_PARENS \
( \
__VA_ARGS__ \
) \
) \
( \
BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \
BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \
) \
(__VA_ARGS__) \
/**/
#endif /* BOOST_VMD_MSVC_V8 */
#endif /* BOOST_PP_VARIADICS */
#endif /* BOOST_VMD_IS_EMPTY_HPP */
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