ISO/IEC TS 19568:2024
(Main)Programming Languages — C++ Extensions for Library Fundamentals
Programming Languages — C++ Extensions for Library Fundamentals
This document describes extensions to the C++ Standard Library (2). These extensions are classes and functions that are likely to be used widely within a program and/or on the interface boundaries between libraries written by different organizations. It is intended that some of the library components be considered for standardization in a future version of C++. At present, they are not part of any C++ standard. The goal of this document is to build more widespread existing practice for an expanded C++ standard library. It gives advice on extensions to those vendors who wish to provide them.
Langages de programmation — Extensions C++ pour la bibliothèque fondamentaux
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Standards Content (Sample)
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Specification
ISO/IEC TS 19568
Third edition
Programming Languages —
2024-08
C++ Extensions for Library
Fundamentals
Langages de programmation — Extensions C++ pour la
bibliothèque fondamentaux
Reference number
© ISO/IEC 2024
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ii
Contents
Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vi
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . viii
1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3 Terms and definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4 General principles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1 Namespaces, headers, and modifications to standard classes . . . . . . . . . . . . 4
4.2 Feature-testing recommendations . . . . . . . . . . . . . . . . . . . . . . . . 5
5 Modifications to the C++ Standard Library . . . . . . . . . . . . . . . . 7
5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5.2 Exception requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
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iii
6 General utilities library . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1 Constness propagation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1.1 Header synopsis . . . . . . . . . . . . 8
6.1.2 Class template propagate_const . . . . . . . . . . . . . . . . . . . 10
6.1.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 10
6.1.2.2 General requirements on T . . . . . . . . . . . . . . . . . 12
6.1.2.3 Requirements on class type T . . . . . . . . . . . . . . . . 12
6.1.2.4 Constructors . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.2.5 Assignment . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1.2.6 Const observers . . . . . . . . . . . . . . . . . . . . . . 14
6.1.2.7 Non-const observers . . . . . . . . . . . . . . . . . . . . 14
6.1.2.8 Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.1.2.9 Relational operators . . . . . . . . . . . . . . . . . . . . 15
6.1.2.10 Specialized algorithms . . . . . . . . . . . . . . . . . . . 18
6.1.2.11 Underlying pointer access . . . . . . . . . . . . . . . . . . 18
6.1.2.12 Hash support . . . . . . . . . . . . . . . . . . . . . . . 18
6.1.2.13 Comparison function objects . . . . . . . . . . . . . . . . 19
6.2 Scope guard support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.2.1 Header synopsis . . . . . . . . . . . . . . . . 20
6.2.2 Class templates scope_exit, scope_fail, and scope_success . . . . . . . 21
6.2.3 Class template unique_resource . . . . . . . . . . . . . . . . . . . . 24
6.2.3.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.2.3.2 Constructors . . . . . . . . . . . . . . . . . . . . . . . . 26
6.2.3.3 Destructor . . . . . . . . . . . . . . . . . . . . . . . . . 27
6.2.3.4 Assignment . . . . . . . . . . . . . . . . . . . . . . . . 27
6.2.3.5 Other member functions . . . . . . . . . . . . . . . . . . 29
6.2.3.6 unique_resource creation . . . . . . . . . . . . . . . . . . 30
6.3 Metaprogramming and type traits . . . . . . . . . . . . . . . . . . . . . . 31
6.3.1 Header synopsis . . . . . . . . . . . . . 31
6.3.2 Other type transformations . . . . . . . . . . . . . . . . . . . . . . 32
6.3.3 Detection idiom . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
7 Function objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.1 Header synopsis . . . . . . . . . . . . . . . . . . 36
7.2 Class template function . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
7.2.2 Construct/copy/destroy . . . . . . . . . . . . . . . . . . . . . . . 38
7.2.3 Modifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
7.2.4 Observers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
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8 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
8.1 Header synopsis . . . . . . . . . . . . . . . . . . . 40
8.2 Non-owning (observer) pointers . . . . . . . . . . . . . . . . . . . . . . . . 41
8.2.1 Class template observer_ptr overview . . . . . . . . . . . . . . . . . 41
8.2.2 observer_ptr constructors . . . . . . . . . . . . . . . . . . . . . . 42
8.2.3 observer_ptr observers . . . . . . . . . . . . . . . . . . . . . . . . 43
8.2.4 observer_ptr conversions . . . . . . . . . . . . . . . . . . . . . . . 43
8.2.5 observer_ptr modifiers . . . . . . . . . . . . . . . . . . . . . . . . 43
8.2.6 observer_ptr specialized algorithms . . . . . . . . . . . . . . . . . . 44
8.2.7 observer_ptr hash support . . . . . . . . . . . . . . . . . . . . . . 45
8.3 Header synopsis . . . . . . . . . . . . . . 45
8.4 Alias template resource_adaptor . . . . . . . . . . . . . . . . . . . . . . . 45
8.4.1 resource_adaptor . . . . . . . . . . . . . . . . . . . . . . . . . . 45
8.4.2 resource_adaptor_imp constructors . . . . . . . . . . . . . . . . . . 47
8.4.3 resource_adaptor_imp member functions . . . . . . . . . . . . . . . 47
9 Iterators library . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
9.1 Header synopsis . . . . . . . . . . . . . . . . . . . 48
9.2 Class template ostream_joiner . . . . . . . . . . . . . . . . . . . . . . . . 48
9.2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
9.2.2 Constructor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
9.2.3 Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
9.2.4 Creation function . . . . . . . . . . . . . . . . . . . . . . . . . . 50
10 Algorithms library . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
10.1 Header synopsis . . . . . . . . . . . . . . . . . . 51
10.2 Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
10.3 Shuffle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
11 Numerics library . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
11.1 Random number generation . . . . . . . . . . . . . . . . . . . . . . . . . 53
11.1.1 Header synopsis . . . . . . . . . . . . . . . 53
11.1.2 Function template randint . . . . . . . . . . . . . . . . . . . . . . 53
© ISO/IEC 2024 — All rights reserved v
© ISO/IEC 2024 – All rights reserved
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Foreword
ISO (the International Organization for Standardization) and IEC (the International
Electrotechnical Commission) form the specialized system for worldwide standardization. National
bodies that are members of ISO or IEC participate in the development of International Standards
through technical committees established by the respective organization to deal with particular
fields of technical activity. ISO and IEC technical committees collaborate in fields of mutual
interest. Other international organizations, governmental and non-governmental, in liaison with
ISO and IEC, also take part in the work.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed
for the different types of document should be noted. This document was drafted in accordance
with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives or
www.iec.ch/members_experts/refdocs).
ISO and IEC draw attention to the possibility that the implementation of this document may
involve the use of (a) patent(s). ISO and IEC take no position concerning the evidence, validity or
applicability of any claimed patent rights in respect thereof. As of the date of publication of this
document, ISO and IEC had not received notice of (a) patent(s) which may be required to
implement this document. However, implementers are cautioned that this may not represent the
latest information, which may be obtained from the patent database available at www.iso.org/
patents and https://patents.iec.ch. ISO and IEC shall not be held responsible for identifying any
or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does
not constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the
World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see
www.iso.org/iso/foreword.html. In the IEC, see www.iec.ch/understanding-standards.
This document was prepared by Joint Technical Committee ISO/IEC JTC 1, Information
technology, Subcommittee SC 22, Programming languages, their environments and system software
interfaces.
This third edition cancels and replaces the second edition (ISO/IEC TS 19568:2017), which has
been technically revised.
The main changes are as follows:
— The document now refers to the C++ language as defined in ISO/IEC 14882:2020; the
previous edition referred to ISO/IEC 14882:2017.
— Removal of features that have been added to ISO/IEC 14882: tuple utilities, logical
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operator traits, rational arithmetic, time utilities, error support, searchers, not_fn,
optional, any, string_view, shared-ownership pointers, memory_resource, search
algorithm, numeric operations (gcd/lcm), source_location.
— New feature: scope guard class templates for guard types that perform automatic actions
on scope exit.
— Feature modification: type-erasing classes now use polymorphic_allocator<>.
Any feedback or questions on this document should be directed to the user’s national standards
body. A complete listing of these bodies can be found at www.iso.org/members.html and
www.iec.ch/national-committees.
© ISO/IEC 2024 — All rights reserved 7
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vii
Introduction [introduction]
In this document, the phrase C++ Standard Library refers to the library described in ISO/IEC
14882:2020, clauses 16–32.
Clauses and subclauses in this document are annotated with a so-called stable name, presented in
square brackets next to the (sub)clause heading (such as "[introduction]" for this clause). Stable
names aid in the discussion and evolution of this document by serving as stable references to
subclauses across editions that are unaffected by changes of subclause numbering.
In addition to the main font for the document body, this document uses
upright monospace font to display C++ source code, some of which forms part of the
normative specification verbatim, italic monospace font for placeholders within source code
that necessary for the specification, but whose spelling is not significant, and ItalicSerifCamelCase
for certain concepts (comprising syntactic and semantic constraints) from the C++ Standard
Library.
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© ISO/IEC 2024 – All rights reserved
viii
TECHNICAL SPECIFICATION ISO/IEC TS 19568:2024(en)
Programming languages —
C++ Extensions for Library Fundamentals
1 Scope [general.scope]
This document describes extensions to the C++ Standard Library (2). These extensions are
classes and functions that are likely to be used widely within a program and/or on the interface
boundaries between libraries written by different organizations.
It is intended that some of the library
...
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