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Add Foreword.
The general text was provided by the ISO CS. A list of incorporated technical specifications was derived from N4824. A list of technical changes since C++17 was derived from P2131R0.
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‎source/front.tex

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\hypertarget{toctarget}{\tableofcontents*}
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\setcounter{tocdepth}{5}
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\input{preface}

‎source/preface.tex

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%!TEX root = std.tex
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\chapter{Foreword}
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ISO (the International Organization for Standardization) and IEC (the
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International Electrotechnical Commission) form the specialized system for
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worldwide standardization. National bodies that are members of ISO or IEC
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participate in the development of International Standards through technical
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committees established by the respective organization to deal with particular
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fields of technical activity. ISO and IEC technical committees collaborate in
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fields of mutual interest. Other international organizations, governmental and
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non-governmental, in liaison with ISO and IEC, also take part in the work.
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The procedures used to develop this document and those intended for its further
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maintenance are described in the ISO/IEC Directives, Part 1. In particular the
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different approval criteria needed for the different types of documents should
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be noted. This document was drafted in accordance with the editorial rules of
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the ISO/IEC Directives, Part 2
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(see \href{http://www.iso.org/directives}{\tcode{www.iso.org/directives}}).
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Attention is drawn to the possibility that some of the elements of this
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document may be the subject of patent rights. ISO and IEC shall not be held
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responsible for identifying any or all such patent rights. Details of any
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patent rights identified during the development of the document will be in the
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Introduction and/or on the ISO list of patent declarations received
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(see \href{http://www.iso.org/patents}{\tcode{www.iso.org/patents}})
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or the IEC list of patent declarations received
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(see \href{http://patents.iec.ch}{\tcode{http://patents.iec.ch}}).
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Any trade name used in this document is information given for the convenience
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of users and does not constitute an endorsement.
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For an explanation on
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the voluntary nature of standards,
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the meaning of ISO specific terms and expressions related
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to conformity assessment, as well as information about ISO's adherence
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to the World Trade Organization (WTO) principles
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in the Technical Barriers to Trade (TBT) see the following URL:
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\href{http://www.iso.org/iso/foreword.html}{\tcode{www.iso.org/iso/foreword.html}}.
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This document was prepared by
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Joint Technical Committee ISO/IEC JTC 1, \textit{Information technology},
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Subcommittee SC 22, \textit{Programming languages, their environments and system software interfaces}.
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This sixth edition cancels and replaces the fifth edition
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(ISO/IEC 14882:2017), which has been technically revised.
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It also incorporates the Technical Specifications
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\begin{itemize}
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\item ISO/IEC TS 19217:2015 \textit{Programming Languages --- \Cpp{} Extensions for concepts},
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\item ISO/IEC TS 21425:2017 \textit{Programming Languages --- \Cpp{} Extensions for ranges},
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\item ISO/IEC TS 22277:2017 \textit{Programming Languages --- \Cpp{} Extensions for Coroutines},
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\item ISO/IEC TS 21544:2018 \textit{Programming Languages --- Extensions to \Cpp{} for Modules},
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\item portions of ISO/IEC TS 19571:2016 \textit{Programming Languages --- Technical specification for \Cpp{} extensions for concurrency}, and % latch and barrier
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\item portions of ISO/IEC TS 19568:2017 \textit{Programming Languages --- \Cpp{} Extensions for Library Fundamentals}.
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\end{itemize}
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The main changes compared to the previous edition are as follows:
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\begin{itemize}
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% language changes
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\item addition of concepts, \grammarterm{requires-clause}s, and \grammarterm{requires-expression}s and
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\libheaderref{concepts} header
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\item addition of coroutines, including
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\keyword{co_yield}, \keyword{co_await}, and \keyword{co_return} keywords and
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\libheaderref{coroutine} header
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\item addition of modules, \grammarterm{import-declaration}s, and \grammarterm{export-declaration}s
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\item addition of three-way comparison, defaulted comparisons,
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rewriting of comparison operator expressions, and \libheaderref{compare} header
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\item addition of designated initializers
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\item support for class types and floating-point types as the type of a non-type template parameter
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\item new attributes \tcode{[[no_unique_address]]}, \tcode{[[likely]]}, \tcode{[[unlikely]]}
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\item support for optional reason string in \tcode{[[nodiscard]]} attribute
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\item ability to require constant initialization with \keyword{constinit} keyword
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\item ability to require constant evaluation with \keyword{consteval} keyword
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\item extension of constant evaluation support to cover
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\begin{itemize}
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\item memory allocation and deallocation
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\item virtual function calls
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\item \keyword{dynamic_cast} and \keyword{typeid}
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\item changing the active member of a union
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\item uninitialized variables
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\end{itemize}
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\item support for constexpr functions to contain
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\keyword{catch} handlers and \grammarterm{asm-declaration}s
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that are not reached during constant evaluation
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\item support for controlling destruction in a class-specific operator delete function
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\item addition of \keyword{using} \keyword{enum} declaration
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\item addition of \keyword{char8_t} type
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\item guarantee that \keyword{char16_t} and \keyword{char32_t} literals
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are encoded as UTF-16 and UTF-32 respectively
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\item support for an initializer statement in range-based for loops
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\item support for default member initializers for bit-fields
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\item support for parenthesized aggregate initialization
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\item extended support for lambda expressions, including
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\begin{itemize}
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\item explicit \grammarterm{template-head}s in generic lambdas
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\item default construction and assignment of stateless closure types
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\item lambda expressions in unevaluated operands
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\item pack expansion of lambda \grammarterm{init-capture}s
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\end{itemize}
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\item generalized support for structured bindings
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\item support for inline namespaces in nested namespace definitions
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\item support for conditionally-explicit member functions
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\item extended support for class template argument deduction to cover
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aggregate initialization and alias templates
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\item reduced cases in which \keyword{typename} is required
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\item support for calling an undeclared \grammarterm{template-id}
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via argument-dependent name lookup
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\item relaxed access checking rules in template specialization declarations
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\item revised memory model
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\item expanded cases in which returned or thrown variables are implicitly moved
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\item extended support for variadic macros with \mname{VA_OPT}
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% library changes
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\item feature test macros and \libheaderref{version} header
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\item restricted valid uses of standard library functions and function templates
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\item addition of ranges and \libheaderref{ranges} header
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\item addition of calendar and time zone support
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\item addition of text formatting library and \libheaderref{format} header
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\item addition of synchronization facilities for
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waiting, notifications, semaphores, latches, and barriers, and
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\libheaderref{barrier}, \libheaderref{latch} and \libheaderref{semaphore} headers
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\item addition of mathematical constants library and \libheaderref{numbers} header
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\item support for representing source locations and \libheaderrefx{source_location}{source.location.syn} header
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\item addition of \tcode{span} view and \libheaderref{span} header
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\item addition of joining thread class and \libheaderrefx{stop_token}{thread.stoptoken.syn} header
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\item extensions to atomic types and operations, including
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\begin{itemize}
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\item new class template \tcode{atomic_ref}
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\item new atomic floating-point operations
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\item new atomic smart pointer types
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\item support for compare-and-exchange operations on types with padding
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\item conversion of \tcode{memory_order} to a scoped enumeration
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\end{itemize}
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\item addition of \tcode{unsequenced} execution policy
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\item new utility functions, types, and templates in the standard library, including
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\begin{itemize}
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\item \raggedright new type traits
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\tcode{is_bounded_array},
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\tcode{is_corresponding_member},
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\tcode{is_layout_compatible},
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\tcode{is_nothrow_convertible},
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\tcode{is_pointer_interconvertible_base_of},
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\tcode{is_pointer_interconvertible_with_class}, and
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\tcode{is_unbounded_array}
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\item new transformation traits
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\tcode{remove_cvref},
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\tcode{type_identity},
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\tcode{unwrap_ref_decay}, and
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\tcode{unwrap_reference}
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\item new standard library primitive functions \tcode{assume_aligned} and
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\tcode{is_constant_evaluated}
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\item new free functions \tcode{erase} and \tcode{erase_if} for containers
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\item utilities for uses-allocator construction
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\item function template \tcode{to_address}
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\item function template \tcode{bind_front}
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\item function template \tcode{to_array}
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\end{itemize}
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\item \tcode{make_shared} support for array types
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\item support for allocating objects owned by \tcode{shared_ptr} and \tcode{unique_ptr}
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with default initialization
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\item addition of bit manipulation library and \libheaderref{bit} header
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\item addition of a synchronized buffered output stream and \libheaderref{syncstream} header
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\item addition of \tcode{shift} algorithms
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\item addition of \tcode{midpoint} and \tcode{lerp} math functions
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\item use of \tcode{[[nodiscard]]} attribute in the standard library
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\item support for heterogeneous lookup for unordered containers
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\item support for element existence detection in associative containers
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\item change to return removed element count
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from \tcode{remove}, \tcode{remove_if}, and \tcode{unique}
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member functions on \tcode{list} and \tcode{forward_list}
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\item addition of \tcode{starts_with} and \tcode{ends_with}
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to \tcode{basic_string} and \tcode{basic_string_view}
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\item support for move semantics in \libheaderrefx{numeric}{numeric.ops.overview} algorithms
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\item support for efficient access to the buffer of a \tcode{basic_stringbuf}
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\item extended constant expression evaluation support in the standard library
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to cover more algorithms, utilities, and types, including
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\tcode{pair}, \tcode{tuple}, \tcode{vector}, and \tcode{string}
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% annexes
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\item removal of deprecated features
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\end{itemize}
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Any feedback or questions on this document
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should be directed to the user's national standards body.
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A complete listing of these bodies can be found at
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\href{http://www.iso.org/members.html}{\tcode{www.iso.org/members.html}}.

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