ISO/IEC 14882:2020

Programming languages - C++

This document specifies requirements for implementations of the C++ programming language. The first such requirement is that they implement the language, so this document also defines C++. Other requirements and relaxations of the first requirement appear at various places within this document. C++ is a general purpose programming language based on the C programming language as described in ISO/IEC 9899:2018 Programming languages - C (hereinafter referred to as the C standard). C++ provides many facilities beyond those provided by C, including additional data types, classes, templates, exceptions, namespaces, operator overloading, function name overloading, references, free store management operators, and additional library facilities.

Langages de programmation — C++

General Information

• Status: Published
• Publication Date: 14-Dec-2020
• ICS: 35.060 - Languages used in information technology
• Technical Committee: ISO/IEC JTC 1/SC 22 - Programming languages, their environments and system software interfaces
• Drafting Committee: ISO/IEC JTC 1/SC 22/WG 21 - C++
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 19-Oct-2024
• Completion Date: 30-Oct-2025

Relations

• Revised: ISO/IEC 14882:2024 - Programming languages - C++
• Effective Date: 06-Jun-2022
• Revises: ISO/IEC 14882:2017 - Programming languages - C++
• Effective Date: 23-Apr-2020

Overview

ISO/IEC 14882:2020 - Programming languages - C++ is the International Standard that specifies requirements for implementations of the C++ programming language. Published as the sixth edition (2020-12), this document both defines the C++ language and sets compliance requirements for compiler and library implementers. It builds on the C standard (ISO/IEC 9899:2018) and describes language syntax, semantics, translation phases, and a comprehensive standard library.

Key topics and technical requirements

The standard covers language and library aspects with detailed, normative requirements. Key technical topics include:

• Implementation compliance - requirements for conformant compilers and library implementations.
• Lexical conventions & translation phases - tokenization, character sets, preprocessing, and separate translation rules.
• Core language rules - declarations, one-definition rule, scope, name lookup, types, memory and object models, and program execution.
• Classes, templates, and overloading - class semantics, member lookup, template parameters, instantiation and specialization, overload resolution.
• Modules and header units - module units, export/import semantics, global/private module fragments, and header unit importation.
• Exception handling and diagnostics - throwing/handling rules, special functions, and diagnostics library requirements.
• Standard library components - language support, containers, strings, smart pointers, formatting, coroutines, concepts, utilities, and more. The table of contents documents sections such as the Language Support Library, Concepts Library, Coroutines, Containers, Strings, and Formatting.
• Preprocessing & macros - conditional inclusion, file inclusion, macro replacement, pragma and error directives.
• Library-wide requirements - behavior guarantees, header names, and interactions with the C standard library.

Practical applications and who uses this standard

ISO/IEC 14882:2020 is essential for:

• Compiler and tool implementers - to build conformant C++ compilers, linkers, and language tooling.
• Standard library and runtime authors - to implement containers, algorithms, memory and type support as required.
• Software architects and developers - to understand guaranteed language behaviors, portability constraints, and portability best practices across platforms.
• Certification and QA teams - to validate conformance, portability, and safety-critical behavior.
• Educators and technical writers - as the definitive language reference for teaching and documentation.

Adhering to ISO/IEC 14882:2020 ensures consistent language semantics, predictable runtime behavior, and portable C++ code across compliant implementations.

Related standards

• ISO/IEC 9899:2018 - Programming languages - C (referenced as the C standard).
• Other ISO/IEC programming language and tool standards relevant to interoperability and conformance testing.

Standards Content (Sample)

INTERNATIONAL ISO/IEC
STANDARD 14882
Sixth edition
2020-12
Programming languages — C++
Langages de programmation — C++
Reference number
©
ISO/IEC 2020
© ISO/IEC 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO/IEC 2020 – All rights reserved

Contents
Foreword x
1 Scope 1
2 Normative references 2
3 Terms and definitions 3
4 General principles 9
4.1 Implementation compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 Structure of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3 Syntax notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5 Lexical conventions 12
5.1 Separate translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2 Phases of translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 Character sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.4 Preprocessing tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.5 Alternative tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.6 Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.7 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.8 Header names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.9 Preprocessing numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.10 Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.11 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.12 Operators and punctuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.13 Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6 Basics 28
6.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.2 Declarations and definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
6.3 One-definition rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
6.4 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
6.5 Name lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
6.6 Program and linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
6.7 Memory and objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.8 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
6.9 Program execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
7 Expressions 90
7.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.2 Properties of expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.3 Standard conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
7.4 Usual arithmetic conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.5 Primary expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.6 Compound expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
7.7 Constant expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
8 Statements 153
8.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
8.2 Labeled statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
8.3 Expression statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
8.4 Compound statement or block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
8.5 Selection statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
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8.6 Iteration statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
8.7 Jump statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
8.8 Declaration statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
8.9 Ambiguity resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
9 Declarations 163
9.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 163
9.2 Specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
9.3 Declarators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
9.4 Initializers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
9.5 Function definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
9.6 Structured binding declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
9.7 Enumerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
9.8 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
9.9 The using declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
9.10 The asm declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 236
9.11 Linkage specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 237
9.12 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
10 Modules 247
10.1 Module units and purviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
10.2 Export declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
10.3 Import declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
10.4 Global module fragment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
10.5 Private module fragment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
10.6 Instantiation context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
10.7 Reachability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
11 Classes 258
11.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
11.2 Properties of classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259
11.3 Class names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260
11.4 Class members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262
11.5 Unions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 284
11.6 Local class declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
11.7 Derived classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
11.8 Member name lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
11.9 Member access control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
11.10 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 308
11.11 Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
11.12 Free store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 322
12 Overloading 324
12.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
12.2 Overloadable declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324
12.3 Declaration matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
12.4 Overload resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 327
12.5 Address of overloaded function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351
12.6 Overloaded operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
12.7 Built-in operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
12.8 User-defined literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
13 Templates 360
13.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
13.2 Template parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 361
13.3 Names of template specializations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 365
13.4 Template arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 368
13.5 Template constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
13.6 Type equivalence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
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13.7 Template declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
13.8 Name resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
13.9 Template instantiation and specialization . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
13.10 Function template specializations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
14 Exception handling 451
14.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
14.2 Throwing an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
14.3 Constructors and destructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
14.4 Handling an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
14.5 Exception specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
14.6 Special functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 458
15 Preprocessing directives 460
15.1 Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
15.2 Conditional inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
15.3 Source file inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 464
15.4 Module directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 465
15.5 Header unit importation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 466
15.6 Macro replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 467
15.7 Line control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 472
15.8 Error directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
15.9 Pragma directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
15.10 Null directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
15.11 Predefined macro names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 473
15.12 Pragma operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 475
16 Library introduction 477
16.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 477
16.2 The C standard library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
16.3 Method of description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 478
16.4 Library-wide requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 484
17 Language support library 505
17.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
17.2 Common definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505
17.3 Implementation properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 509
17.4 Integer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 519
17.5 Startup and termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 520
17.6 Dynamic memory management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 522
17.7 Type identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 529
17.8 Source location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 530
17.9 Exception handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 532
17.10 Initializer lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
17.11 Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
17.12 Coroutines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 545
17.13 Other runtime support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 549
18 Concepts library 552
18.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
18.2 Equality preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 552
18.3 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
18.4 Language-related concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 555
18.5 Comparison concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 560
18.6 Object concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
18.7 Callable concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563
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19 Diagnostics library 565
19.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
19.2 Exception classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 565
19.3 Assertions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
19.4 Error numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 568
19.5 System error support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 570
20 General utilities library 579
20.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
20.2 Utility components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 579
20.3 Compile-time integer sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 584
20.4 Pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 585
20.5 Tuples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 589
20.6 Optional objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 599
20.7 Variants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 611
20.8 Storage for any type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 622
20.9 Bitsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 627
20.10 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 632
20.11 Smart pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 648
20.12 Memory resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 671
20.13 Class template scoped_allocator_adaptor . . . . . . . . . . . . . . . . . . . . . . . . . . 680
20.14 Function objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 684
20.15 Metaprogramming and type traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 707
20.16 Compile-time rational arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 732
20.17 Class type_index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 734
20.18 Execution policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 736
20.19 Primitive numeric conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 738
20.20 Formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 740
21 Strings library 759
21.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
21.2 Character traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 759
21.3 String classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 764
21.4 String view classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 790
21.5 Null-terminated sequence utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800
22 Containers library 805
22.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
22.2 Container requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 805
22.3 Sequence containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 839
22.4 Associative containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 867
22.5 Unordered associative containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 885
22.6 Container adaptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 906
22.7 Views . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 914
23 Iterators library 921
23.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 921
23.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 921
23.3 Iterator requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 928
23.4 Iterator primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 948
23.5 Iterator adaptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 951
23.6 Stream iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 972
23.7 Range access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 978
24 Ranges library 980
24.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 980
24.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 980
24.3 Range access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985
24.4 Range requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 989
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24.5 Range utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 992
24.6 Range factories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 997
24.7 Range adaptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1007
25 Algorithms library 1044
25.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044
25.2 Algorithms requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1044
25.3 Parallel algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046
25.4 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1049
25.5 Algorithm result types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1084
25.6 Non-modifying sequence operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1087
25.7 Mutating sequence operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1099
25.8 Sorting and related operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1115
25.9 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1142
25.10 Generalized numeric operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1145
25.11 Specialized algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154
25.12 C library algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1160
26 Numerics library 1161
26.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1161
26.2 Numeric type requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1161
26.3 The floating-point environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1161
26.4 Complex numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1162
26.5 Bit manipulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1170
26.6 Random number generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1173
26.7 Numeric arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1210
26.8 Mathematical functions for floating-point types . . . . . . . . . . . . . . . . . . . . . . . . 1229
26.9 Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1244
27 Time library 1245
27.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
27.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1245
27.3 Cpp17Clock requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
27.4 Time-related traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1259
27.5 Class template duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1261
27.6 Class template time_point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1268
27.7 Clocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1271
27.8 The civil calendar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1282
27.9 Class template hh_mm_ss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1311
27.10 12/24 hours functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313
27.11 Time zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313
27.12 Formatting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1326
27.13 Parsing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1330
27.14 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1334
28 Localization library 1335
28.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1335
28.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1335
28.3 Locales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1336
28.4 Standard locale categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
28.5 C library locales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1374
29 Input/output library 1375
29.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375
29.2 Iostreams requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1375
29.3 Forward declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1376
29.4 Standard iostream objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1378
29.5 Iostreams base classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1380
29.6 Stream buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1395
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29.7 Formatting and manipulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1403
29.8 String-based streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1427
29.9 File-based streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1441
29.10 Synchronized output streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1453
29.11 File systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1458
29.12 C library files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1503
30 Regular expressions library 1506
30.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1506
30.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1506
30.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1507
30.4 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1508
30.5 Namespace std::regex_constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1512
30.6 Class regex_error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1515
30.7 Class template regex_traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1515
30.8 Class template basic_regex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1517
30.9 Class template sub_match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1522
30.10 Class template match_results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1523
30.11 Regular expression algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1528
30.12 Regular expression iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1532
30.13 Modified ECMAScript regular expression grammar . . . . . . . . . . . . . . . . . . . . . . 1537
31 Atomic operations library 1540
31.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1540
31.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1540
31.3 Type aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1544
31.4 Order and consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1544
31.5 Lock-free property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1546
31.6 Waiting and notifying . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1546
31.7 Class template atomic_ref . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1547
31.8 Class template atomic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1553
31.9 Non-member functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1568
31.10 Flag type and operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1568
31.11 Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1570
32 Thread support library 1572
32.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1572
32.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1572
32.3 Stop tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1574
32.4 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1579
32.5 Mutual exclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1586
32.6 Condition variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1605
32.7 Semaphore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1612
32.8 Coordination types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1614
32.9 Futures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1617
Annex A Grammar summary 1632
A.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1632
A.2 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1632
A.3 Lexical conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1632
A.4 Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1636
A.5 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1637
A.6 Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1641
A.7 Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1641
A.8 Modules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1647
A.9 Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1648
A.10 Overloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1649
A.11 Templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1649
A.12 Exception handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1651
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A.13 Preprocessing directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1651
Annex B Implementation quantities 1653
Annex C Compatibility 1655
++ ++
C.1 C and ISO C 2017 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1655
++ ++
C.2 C and ISO C 2014 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1662
++ ++
C.3 C and ISO C 2011 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1666
++ ++
C.4 C and ISO C 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1667
++
C.5 C and ISO C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1673
C.6 C standard library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1681
Annex D Compatibility features 1683
D.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683
D.2 Arithmetic conversion on enumerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683
D.3 Implicit capture of *this by reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683
D.4 Comma operator in subscript expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683
D.5 Array comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1683
D.6 Deprecated volatile types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1684
D.7 Redeclaration of static constexpr data members . . . . . . . . . . . . . . . . . . . . . . 1684
D.8 Non-local use of TU-local entities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1685
D.9 Implicit declaration of copy functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1685
D.10 C headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1685
D.11 Requires paragraph . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1686
D.12 Relational operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1686
D.13 char* streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1687
D.14 Deprecated type traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1694
D.15 Tuple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1695
D.16 Variant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1695
D.17 Deprecated iterator class template . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1696
D.18 Deprecated move_iterator access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1696
D.19 Deprecated shared_ptr atomic access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1696
D.20 Deprecated basic_string capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1698
D.21 Deprecated standard code conversion facets . . . . . . . . . . . . . . . . . . . . . . . . . . 1698
D.22 Deprecated convenience conversion interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 1700
D.23 Deprecated locale category facets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1703
D.24 Deprecated filesystem path factory functions . . . . . . . . . . . . . . . . . . . . . . . . . . 1704
D.25 Deprecated atomic operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1704
Bibliography 1706
Cross references 1707
++
Cross references from ISO C 2017 1731
Index 1734
Index of grammar productions 1768
Index of library headers 1773
Index of library names 1775
Index of library concepts 1847
Index of implementation-defined behavior 1850
Contents ©ISO/IEC 2020 – All rights reserved ix

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).
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO and IEC shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on the
ISO list of patent declarations received (see www.iso.org/patents) or the IEC list of patent declarations
received (see http://patents.iec.ch).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions re-
lated 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.
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 sixth edition cancels and replaces the fifth edition (ISO/IEC 14882:2017), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— inclusion of the provisions of ISO/IEC TS 19217:2015, ISO/IEC TS 21425:2017, ISO/IEC TS 22277:2017,
ISO/IEC TS 21544:2018, portions of ISO/IEC TS 19571:2016, and portions of ISO/IEC TS 19568:2017.
— addition of concepts, requires-clauses, requires-expressions, and (18.3) header
— addition of coroutines, including co_yield, co_await, and co_return keywords and
(17.12.2) header
— addition of modules, import-declarations, and export-declarations
— addition of three-way comparison, defaulted comparisons, rewriting of comparison operator expressions,
and (17.11.1) header
— addition of designated initializers
— support for class types and floating-point types as the type of a non-type template parameter
— new attributes [[no_unique_address]], [[likely]], [[unlikely]]
— support for optional reason string in [[nodiscard]] attribute
— ability to require constant initialization with constinit keyword
— ability to require constant evaluation with consteval keyword
— extensions to constant evaluation
— support for controlling destruction in a class-specific operator delete function
— addition of using enum declaration
— addition of char8_t type
— support for an initializer statement in range-based for loops
Foreword ©ISO/IEC 2020 – All rights reserved x

— support for default member initializers for bit-fields
— support for parenthesized aggregate initialization
— extensions to lambda expressions
— extensions to structured bindings
— support for inline namespaces in nested namespace definitions
— support for conditionally-explicit member functions
— extensions to class template argument deduction
— reduced cases in which typename is required
— support for calling an undeclared template-id via argument-dependent name lookup
— revised memory model
— extended support for variadic macros with __VA_OPT__
— feature test macros and (17.3.2) header
— addition of ranges and (24.2) header
— addition of calendar and time zone support
— addition of text formatting library and (20.20.1) header
— addition of (32.8.3.2), (32.8.2.2), and (32.7.2) headers
— addition of mathematical constants library and (26.9.1) header
— support for representing source locations and (17.8.1) header
— addition of span view and (22.7.2) header
— addition of joining thread class and (32.3.2) header
— extensions to atomic types and operations
— addition of unsequenced execution policy
— new utility functions, types, and templates in the standard library
— addition of bit manipulation library and (26.5.2) header
— addition of a synchronized buffered output stream and (29.10.1) header
— support for heterogeneous lookup for unordered containers
— support for element existence detection in associative containers
— support for move semantics in (25.9) algorithms
— support for efficient access to the buffer of a basic_stringbuf
— extended constant expression evaluation support in the standard library
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.
Foreword ©ISO/IEC 2020 – All rights reserved xi

1 Scope [intro.scope]
++
This document specifies requirements for implementations of the C programming language. The first such
++
requirement is that they implement the language, so this document also defines C . Other requirements
and relaxations of the first requirement appear at various places within this document.
2 ++
C is a general purpose programming language based on the C programming language as described in
++
ISO/IEC 9899:2018 Programming languages — C (hereinafter referred to as the C standard). C provides
many facilities beyond those provided by C, including additional data types, classes, templates, exceptions,
namespaces, operator overloading, function name overloading, references, free store management operators,
and additional library facilities.
Scope ©ISO/IEC 2020 – All rights reserved 1

2 Normative references [intro.refs]
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
(1.1)
— ISO/IEC 2382, Information technology — Vocabulary
(1.2)
— ISO 8601:2004, Data elements and interchange formats — Information interchange — Representation
of dates and times
(1.3)
— ISO/IEC 9899:2018, Programming languages — C
(1.4)
— ISO/IEC 9945:2003, Information Technology — Portable Operating System Interface (POSIX )
(1.5)
— ISO/IEC 10646, Information technology — Universal Coded Character Set (UCS)
(1.6)
— ISO/IEC 10646:2003, Information technology — Universal Multiple-Octet Coded Character Set (UCS)
(1.7)
— ISO 80000-2:2009, Quantities and units — Part 2: Mathematical signs and symbols to be used in the
natural sciences and technology
(1.8)
— Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999.
The library described in ISO/IEC 9899:2018, Clause 7, is hereinafter called the C standard library.
The operating system interface described in ISO/IEC 9945:2003 is hereinafter called POSIX.
The ECMAScript Language Specification described in Standard Ecma-262 is hereinafter called ECMA-262.
[Note 1: References to ISO/IEC 10646:2003 are used only to support deprecated features (D.21). —end note]
1) POSIX® is a registered trademark of the Institute of Electrical and Electronic Engineers, Inc.
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