mirror of http://192.168.1.51:8099/lmh188/twain3.0
120 lines
3.4 KiB
C++
120 lines
3.4 KiB
C++
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// (C) Copyright Edward Diener 2011-2015,2019
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// Use, modification and distribution are subject to the Boost Software License,
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// Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt).
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#if !defined(BOOST_VMD_IS_EMPTY_HPP)
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#define BOOST_VMD_IS_EMPTY_HPP
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#include <boost/vmd/detail/setup.hpp>
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#if BOOST_PP_VARIADICS
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#include <boost/preprocessor/punctuation/is_begin_parens.hpp>
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#include <boost/vmd/detail/is_empty.hpp>
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/*
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The succeeding comments in this file are in doxygen format.
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*/
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/** \file
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*/
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/** \def BOOST_VMD_IS_EMPTY(...)
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\brief Tests whether its input is empty or not.
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The macro checks to see if the input is empty or not.
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It returns 1 if the input is empty, else returns 0.
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The macro is a variadic macro taking any input.
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For the VC++8 compiler (VS2005) the macro takes a single parameter of input to check.
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For all levels of C++ prior to C++20 the macro is not perfect,
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and can not be so. The problem area is if the input to be
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checked is a function-like macro name, in which case either
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a compiler error can result or a false result can occur.
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For C++20, with its support for the new __VA_OPT__ preprocessor
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construct, the macro will always work correctly no matter what
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the variadic input, and is therefore 100% reliable.
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This macro is a replacement, using variadic macro support,
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for the undocumented macro BOOST_PP_IS_EMPTY in the Boost
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PP library. The code is taken from a posting by Paul Mensonides
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of a variadic version for BOOST_PP_IS_EMPTY, and changed
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in order to also support VC++. The code for the C++20
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implementation of the macro, using the __VA_OPT__ preprocessor
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construct, is the author's own and reuses code added to the
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Boost preprocessor library by this author.
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... = variadic input, for VC++8 this must be a single parameter
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returns = 1 if the input is empty, 0 if it is not
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It is recommended to append BOOST_PP_EMPTY() to whatever input
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is being tested in order to avoid possible warning messages
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from some compilers about no parameters being passed to the macro
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when the input is truly empty.
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*/
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#if BOOST_VMD_MSVC_V8
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#define BOOST_VMD_IS_EMPTY(sequence) \
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BOOST_VMD_DETAIL_IS_EMPTY_IIF \
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( \
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BOOST_PP_IS_BEGIN_PARENS \
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( \
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sequence \
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) \
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) \
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( \
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BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \
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BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \
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) \
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(sequence) \
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/**/
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#else
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# if defined(__cplusplus) && __cplusplus > 201703L
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#include <boost/preprocessor/variadic/has_opt.hpp>
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#include <boost/preprocessor/facilities/is_empty.hpp>
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#define BOOST_VMD_IS_EMPTY(...) \
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BOOST_VMD_DETAIL_IS_EMPTY_IIF \
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( \
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BOOST_PP_VARIADIC_HAS_OPT() \
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) \
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( \
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BOOST_PP_IS_EMPTY_OPT, \
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BOOST_VMD_IS_EMPTY_NO_OPT \
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) \
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(__VA_ARGS__) \
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/**/
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# else
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#define BOOST_VMD_IS_EMPTY(...) \
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BOOST_VMD_IS_EMPTY_NO_OPT(__VA_ARGS__) \
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/**/
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# endif
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#define BOOST_VMD_IS_EMPTY_NO_OPT(...) \
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BOOST_VMD_DETAIL_IS_EMPTY_IIF \
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( \
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BOOST_PP_IS_BEGIN_PARENS \
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( \
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__VA_ARGS__ \
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) \
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) \
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( \
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BOOST_VMD_DETAIL_IS_EMPTY_GEN_ZERO, \
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BOOST_VMD_DETAIL_IS_EMPTY_PROCESS \
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) \
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(__VA_ARGS__) \
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/**/
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#endif /* BOOST_VMD_MSVC_V8 */
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#endif /* BOOST_PP_VARIADICS */
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#endif /* BOOST_VMD_IS_EMPTY_HPP */
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