ISO/IEC 14882:2017

Programming languages - C++

ISO/IEC 14882:2017 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 9899:2011 Programming languages ? C (hereinafter referred to as the C standard). In addition to the facilities provided by C, C++ provides 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• Status: Withdrawn
• Publication Date: 29-Nov-2017
• Withdrawal Date: 29-Nov-2017
• 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: 15-Dec-2020
• Completion Date: 30-Oct-2025

Relations

• Revised: ISO/IEC 14882:2020 - Programming languages - C++
• Effective Date: 23-Apr-2020
• Revises: ISO/IEC 14882:2014 - Information technology - Programming languages - C++
• Effective Date: 05-Nov-2015

Standards Content (Sample)

INTERNATIONAL ISO/IEC
STANDARD 14882
Fifth edition
2017-12
Programming languages — C++
Langages de programmation — C++
Reference number
© ISO/IEC 2017
© ISO/IEC 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
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Tel. [phone]
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[e-mail]
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ii © ISO/IEC 2017 – All rights reserved

Contents
Foreword xi
1 Scope 1
2 Normative references 2
3 Terms and definitions 3
4 General principles 7
4.1 Implementation compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2 Structure of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3 Syntax notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
++
4.4 The C memory model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
++
4.5 The C object model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.6 Program execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.7 Multi-threaded executions and data races . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5 Lexical conventions 22
5.1 Separate translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2 Phases of translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.3 Character sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4 Preprocessing tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.5 Alternative tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.6 Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.7 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.8 Header names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.9 Preprocessing numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.10 Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.11 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.12 Operators and punctuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.13 Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6 Basic concepts 39
6.1 Declarations and definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.2 One-definition rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.4 Name lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.5 Program and linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.6 Start and termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.7 Storage duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
6.8 Object lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.9 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.10 Lvalues and rvalues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.11 Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Contents ©ISO/IEC 2017 – All rights reserved iii

7 Standard conversions 86
7.1 Lvalue-to-rvalue conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.2 Array-to-pointer conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.3 Function-to-pointer conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.4 Temporary materialization conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.5 Qualification conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.6 Integral promotions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.7 Floating-point promotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.8 Integral conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.9 Floating-point conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.10 Floating-integral conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.11 Pointer conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.12 Pointer to member conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.13 Function pointer conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.14 Boolean conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.15 Integer conversion rank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
8 Expressions 93
8.1 Primary expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.2 Postfix expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
8.3 Unary expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
8.4 Explicit type conversion (cast notation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
8.5 Pointer-to-member operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8.6 Multiplicative operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
8.7 Additive operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
8.8 Shift operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
8.9 Relational operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
8.10 Equality operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
8.11 Bitwise AND operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.12 Bitwise exclusive OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.13 Bitwise inclusive OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.14 Logical AND operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.15 Logical OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.16 Conditional operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
8.17 Throwing an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
8.18 Assignment and compound assignment operators . . . . . . . . . . . . . . . . . . . . . . . 137
8.19 Comma operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
8.20 Constant expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
9 Statements 144
9.1 Labeled statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.2 Expression statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.3 Compound statement or block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.4 Selection statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.5 Iteration statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
9.6 Jump statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
9.7 Declaration statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.8 Ambiguity resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
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10 Declarations 155
10.1 Specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
10.2 Enumeration declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
10.3 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
10.4 The asm declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.5 Linkage specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.6 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
11 Declarators 201
11.1 Type names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
11.2 Ambiguity resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
11.3 Meaning of declarators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
11.4 Function definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
11.5 Structured binding declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
11.6 Initializers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
12 Classes 237
12.1 Class names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
12.2 Class members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
12.3 Unions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
12.4 Local class declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
13 Derived classes 255
13.1 Multiple base classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
13.2 Member name lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
13.3 Virtual functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
13.4 Abstract classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
14 Member access control 267
14.1 Access specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
14.2 Accessibility of base classes and base class members . . . . . . . . . . . . . . . . . . . . . . 269
14.3 Friends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
14.4 Protected member access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
14.5 Access to virtual functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
14.6 Multiple access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
14.7 Nested classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
15 Special member functions 278
15.1 Constructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
15.2 Temporary objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
15.3 Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
15.4 Destructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
15.5 Free store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
15.6 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
15.7 Construction and destruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
15.8 Copying and moving class objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
16 Overloading 309
16.1 Overloadable declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
16.2 Declaration matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
16.3 Overload resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
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16.4 Address of overloaded function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
16.5 Overloaded operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
16.6 Built-in operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
17 Templates 342
17.1 Template parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
17.2 Names of template specializations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
17.3 Template arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
17.4 Type equivalence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
17.5 Template declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
17.6 Name resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
17.7 Template instantiation and specialization . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
17.8 Function template specializations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
17.9 Deduction guides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
18 Exception handling 422
18.1 Throwing an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
18.2 Constructors and destructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
18.3 Handling an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
18.4 Exception specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
18.5 Special functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430
19 Preprocessing directives 432
19.1 Conditional inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
19.2 Source file inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
19.3 Macro replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
19.4 Line control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
19.5 Error directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.6 Pragma directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.7 Null directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.8 Predefined macro names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.9 Pragma operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
20 Library introduction 445
20.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
20.2 The C standard library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
20.3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
20.4 Method of description (Informative) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
20.5 Library-wide requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
21 Language support library 476
21.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
21.2 Common definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
21.3 Implementation properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
21.4 Integer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
21.5 Start and termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
21.6 Dynamic memory management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
21.7 Type identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
21.8 Exception handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
21.9 Initializer lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
21.10 Other runtime support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
Contents ©ISO/IEC 2017 – All rights reserved vi

22 Diagnostics library 511
22.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
22.2 Exception classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
22.3 Assertions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
22.4 Error numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
22.5 System error support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
23 General utilities library 528
23.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
23.2 Utility components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
23.3 Compile-time integer sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
23.4 Pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
23.5 Tuples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
23.6 Optional objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
23.7 Variants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
23.8 Storage for any type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
23.9 Bitsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586
23.10 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
23.11 Smart pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607
23.12 Memory resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
23.13 Class template scoped_allocator_adaptor . . . . . . . . . . . . . . . . . . . . . . . . . . 645
23.14 Function objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
23.15 Metaprogramming and type traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
23.16 Compile-time rational arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
23.17 Time utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
23.18 Class type_index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
23.19 Execution policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
24 Strings library 723
24.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723
24.2 Character traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723
24.3 String classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
24.4 String view classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
24.5 Null-terminated sequence utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772
25 Localization library 778
25.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
25.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
25.3 Locales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 780
25.4 Standard locale categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
25.5 C library locales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825
26 Containers library 826
26.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
26.2 Container requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
26.3 Sequence containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864
26.4 Associative containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896
26.5 Unordered associative containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918
26.6 Container adaptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 942
Contents ©ISO/IEC 2017 – All rights reserved vii

27 Iterators library 952
27.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
27.2 Iterator requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
27.3 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958
27.4 Iterator primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961
27.5 Iterator adaptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 964
27.6 Stream iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977
27.7 Range access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 984
27.8 Container access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985
28 Algorithms library 986
28.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 986
28.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 986
28.3 Algorithms requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005
28.4 Parallel algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006
28.5 Non-modifying sequence operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1009
28.6 Mutating sequence operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1017
28.7 Sorting and related operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1027
28.8 C library algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046
29 Numerics library 1047
29.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
29.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
29.3 Numeric type requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
29.4 The floating-point environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1048
29.5 Complex numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1049
29.6 Random number generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1059
29.7 Numeric arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1102
29.8 Generalized numeric operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122
29.9 Mathematical functions for floating-point types . . . . . . . . . . . . . . . . . . . . . . . . 1136
30 Input/output library 1153
30.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1153
30.2 Iostreams requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154
30.3 Forward declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154
30.4 Standard iostream objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1156
30.5 Iostreams base classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1158
30.6 Stream buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1175
30.7 Formatting and manipulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
30.8 String-based streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1211
30.9 File-based streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221
30.10 File systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
30.11 C library files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1288
31 Regular expressions library 1292
31.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1292
31.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1292
31.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1293
31.4 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1295
31.5 Namespace std::regex_constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1301
31.6 Class regex_error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304
Contents ©ISO/IEC 2017 – All rights reserved viii

31.7 Class template regex_traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1305
31.8 Class template basic_regex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307
31.9 Class template sub_match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313
31.10 Class template match_results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1318
31.11 Regular expression algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1324
31.12 Regular expression iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1329
31.13 Modified ECMAScript regular expression grammar . . . . . . . . . . . . . . . . . . . . . . 1335
32 Atomic operations library 1338
32.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1338
32.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1338
32.3 Type aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
32.4 Order and consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
32.5 Lock-free property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1344
32.6 Class template atomic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1345
32.7 Non-member functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1352
32.8 Flag type and operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1352
32.9 Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1353
33 Thread support library 1355
33.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
33.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
33.3 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1358
33.4 Mutual exclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1363
33.5 Condition variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1384
33.6 Futures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1391
A Grammar summary 1408
A.1 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1408
A.2 Lexical conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1408
A.3 Basic concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1413
A.4 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1413
A.5 Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1417
A.6 Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1418
A.7 Declarators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1422
A.8 Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1424
A.9 Derived classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425
A.10 Special member functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426
A.11 Overloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426
A.12 Templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426
A.13 Exception handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1427
A.14 Preprocessing directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1428
B Implementation quantities 1430
C Compatibility 1432
++
C.1 C and ISO C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1432
++ ++
C.2 C and ISO C 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1441
++ ++
C.3 C and ISO C 2011 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1447
++ ++
C.4 C and ISO C 2014 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1449
C.5 C standard library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1453
Contents ©ISO/IEC 2017 – All rights reserved ix

D Compatibility features 1456
D.1 Redeclaration of static constexpr data members . . . . . . . . . . . . . . . . . . . . . . 1456
D.2 Implicit declaration of copy functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1456
D.3 Deprecated exception specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1456
++
D.4 C standard library headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1456
D.5 C standard library headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457
D.6 char* streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457
D.7 uncaught_exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1466
D.8 Old adaptable function bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1466
D.9 The default allocator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1471
D.10 Raw storage iterator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1472
D.11 Temporary buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1473
D.12 Deprecated type traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1474
D.13 Deprecated iterator primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1475
D.14 Deprecated shared_ptr observers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1475
D.15 Deprecated standard code conversion facets . . . . . . . . . . . . . . . . . . . . . . . . . . 1475
D.16 Deprecated convenience conversion interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 1477
Bibliography 1482
Cross references 1483
++
Cross references from ISO C 2014 1504
Index 1506
Index of grammar productions 1539
Index of library names 1543
Index of implementation-defined behavior 1601
Contents ©ISO/IEC 2017 – All rights reserved x

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has
been established has the right to be represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
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 ISO documents 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 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).
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 ex-
pressions 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 the following URL:
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee
SC 22, Programming languages, their environments and system software interfaces.
This fifth edition cancels and replaces the fourth edition (ISO/IEC 14882:2014), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— expression evaluation order is specified in more cases
— removal of trigraphs
— adjustments to value categories resulting in copy elision being mandatory
— additional character and floating point literal syntaxes
— lambda expressions extended to permit capture of *this and use in constant expressions
— initializer statements for if and switch statements
— addition of constexpr if statements
— range-based for statement generalized to support heterogeneous begin and end types
— addition of structured bindings
— addition of inline variables
— list initialization extended to support enumerations and aggregates with base classes
— message in static_assert is now optional
— addition of nested namespace definition syntax
Foreword ©ISO/IEC 2017 – All rights reserved xi

— extended support for attributes
— exception specifications are now part of function types
— template argument deduction is now supported for class templates
— addition of fold expressions
— pack expansion can be performed on using declarations
— permitted forms of template parameters and template arguments have been generalized
— dynamic allocation is supported for over-aligned types
— preprocessor can detect presence of header files with __has_include
— new utility functions, types, and templates in the standard library, including
— an any type
— an optional class template
— a variant class template
— a clamp function
— a std::byte type
— a not_fn function
— a void_t alias template
— conjunction, disjunction, and negation templates
— an invoke function, and is_invocable and invoke_result type traits
— an is_swappable type trait
— extended constant expression evaluation support in the standard library
— elementary conversion functions between strings and numeric types added
— constructors for pair and tuple are conditionally-explicit
— shared_ptrs of array types now supported
— additional algorithms for managing uninitialized memory
— addition of polymorphic memory resources
— addition of substring search facilities providing the Boyer-Moore and Boyer-Moore-Horspool search
algorithms
— addition of variable templates for type traits
— addition of a non-owning string view template
— ability to splice elements between containers for maps and sets
— better support for element insertion in unique-key maps
— support for incomplete types in containers
— addition of parallel algorithms
— addition of sample algorithm
— addition of mathematical special functions, and gcd, lcm, and three-argument hypot functions
— addition of support for operations on file systems
— addition of shared mutexes and variadic lock guards
— removal of deprecated features
Foreword ©ISO/IEC 2017 – All rights reserved xii

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.
++
C is a general purpose programming language based on the C programming language as described in
ISO/IEC 9899:2011 Programming languages — C (hereinafter referred to as the C standard). In addition to
++
the facilities provided by C, C provides additional data types, classes, templates, exceptions, namespaces,
operator overloading, function name overloading, references, free store management operators, and additional
library facilities.
Scope ©ISO/IEC 2017 – 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)
— Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999.
(1.2)
— ISO/IEC 2382 (all parts), Information technology — Vocabulary
(1.3)
— ISO/IEC 9899:2011, Programming languages — C
(1.4)
— ISO/IEC 9945:2003, Information Technology — Portable Operating System Interface (POSIX)
(1.5)
— ISO/IEC 10646-1:1993, Information technology — Universal Multiple-Octet Coded Character Set (UCS)
— Part 1: Architecture and Basic Multilingual Plane
(1.6)
— ISO/IEC/IEEE 60559:2011, Information technology — Microprocessor Systems — Floating-Point
arithmetic
(1.7)
— ISO 80000-2:2009, Quantities and units — Part 2: Mathematical signs and symbols to be used in the
natural sciences and technology
The library described in Clause 7 of ISO/IEC 9899:2011 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.
++
1) With the qualifications noted in Clauses 21 through 33 and in C.5, the C standard library is a subset of the C standard
library.
Normative references ©ISO/IEC 2017 – All rights reserved 2

3 Terms and definitions [intro.defs]
For the purposes of this document, the terms and definitions given in ISO/IEC 2382-1:1993, the terms,
definitions, and symbols given in ISO 80000-2:2009, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
(2.1)
— ISO Online browsing platform: available at http://www.iso.org/obp
(2.2)
— IEC Electropedia: available at http://www.electropedia.org/
20.3 defines additional terms that are used only in Clauses 20 through 33 and Annex D.
Terms that are used only in a small portion of this document are defined where they are used and italicized
where they are defined.
3.1 [defns.access]
access
〈execution-time action〉 read or modify the value of an object
3.2 [defns.argument]
argument
〈function call expression〉 expression in the comma-separated list bounded by the parentheses (8.2.2)
3.3 [defns.argument.macro]
argument
〈function-like macro〉 sequence of preprocessing tokens in the comma-separated list bounded by the parenthe-
ses (19.3)
3.4 [defns.argument.throw]
argument
〈throw expression〉 operand of throw (8.17)
3.5 [defns.argument.templ]
argument
〈template instantiation〉 constant-expression, type-id, or id-expression in the comma-separated list bounded
by the angle brackets (17.3)
3.6 [defns.block]
block
wait for some condition (other than for the implementation to execute the execution steps of the thread of
execution) to be satisfied before continuing execution past the blocking operation
3.7 [defns.cond.supp]
conditionally-supported
program construct that an implementation is not required to support
[Note 1 to entry: Each implementation documents all conditionally-supported constructs that it does not
support. —end note]
3.8 [defns.diagnostic]
diagnostic message
message belonging to an implementation-defined subset of the implementation’s output messages
§ 3.8 ©ISO/IEC 2017 – All rights reserved 3

3.9 [defns.dynamic.type]
dynamic type
〈glvalue〉 type of the most derived object (4.5) to which the glvalue refers
[Example: If a pointer (11.3.1) p whose static type is “pointer to class B” is pointing to an object of class D,
derived from B (Clause 13), the dynamic type of the expression *p is “D”. References (11.3.2) are treated
similarly. —end example]
3.10 [defns.dynamic.type.prvalue]
dynamic type
〈prvalue〉 static type of the prvalue expression
3.11 [defns.ill.formed]
ill-formed program
program that is not well-formed (3.29)
3.12 [defns.impl.defined]
implementation-defined behavior
behavior, for a well-formed program construct and correct data, that depend
...

INTERNATIONAL ISO/IEC
STANDARD 14882
Fifth edition
2017-12
Programming languages — C++
Langages de programmation — C++
Reference number
©
ISO/IEC 2017
© ISO/IEC 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO/IEC 2017 – All rights reserved

Contents
Foreword xi
1 Scope 1
2 Normative references 2
3 Terms and definitions 3
4 General principles 7
4.1 Implementation compliance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2 Structure of this document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3 Syntax notation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
++
4.4 The C memory model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
++
4.5 The C object model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.6 Program execution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.7 Multi-threaded executions and data races . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
5 Lexical conventions 22
5.1 Separate translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.2 Phases of translation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.3 Character sets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
5.4 Preprocessing tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.5 Alternative tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.6 Tokens . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.7 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.8 Header names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.9 Preprocessing numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
5.10 Identifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.11 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
5.12 Operators and punctuators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
5.13 Literals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
6 Basic concepts 39
6.1 Declarations and definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
6.2 One-definition rule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
6.3 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
6.4 Name lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.5 Program and linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.6 Start and termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.7 Storage duration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
6.8 Object lifetime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
6.9 Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
6.10 Lvalues and rvalues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.11 Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
Contents ©ISO/IEC 2017 – All rights reserved iii

7 Standard conversions 86
7.1 Lvalue-to-rvalue conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.2 Array-to-pointer conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
7.3 Function-to-pointer conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.4 Temporary materialization conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.5 Qualification conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
7.6 Integral promotions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.7 Floating-point promotion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.8 Integral conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
7.9 Floating-point conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.10 Floating-integral conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.11 Pointer conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.12 Pointer to member conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
7.13 Function pointer conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.14 Boolean conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
7.15 Integer conversion rank . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
8 Expressions 93
8.1 Primary expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
8.2 Postfix expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
8.3 Unary expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
8.4 Explicit type conversion (cast notation) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
8.5 Pointer-to-member operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130
8.6 Multiplicative operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
8.7 Additive operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
8.8 Shift operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
8.9 Relational operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
8.10 Equality operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
8.11 Bitwise AND operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.12 Bitwise exclusive OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.13 Bitwise inclusive OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.14 Logical AND operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.15 Logical OR operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
8.16 Conditional operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
8.17 Throwing an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
8.18 Assignment and compound assignment operators . . . . . . . . . . . . . . . . . . . . . . . 137
8.19 Comma operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
8.20 Constant expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
9 Statements 144
9.1 Labeled statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.2 Expression statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.3 Compound statement or block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.4 Selection statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
9.5 Iteration statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 148
9.6 Jump statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
9.7 Declaration statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.8 Ambiguity resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
Contents ©ISO/IEC 2017 – All rights reserved iv

10 Declarations 155
10.1 Specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
10.2 Enumeration declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
10.3 Namespaces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
10.4 The asm declaration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.5 Linkage specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.6 Attributes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
11 Declarators 201
11.1 Type names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
11.2 Ambiguity resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203
11.3 Meaning of declarators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
11.4 Function definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 216
11.5 Structured binding declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
11.6 Initializers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
12 Classes 237
12.1 Class names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
12.2 Class members . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
12.3 Unions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
12.4 Local class declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254
13 Derived classes 255
13.1 Multiple base classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256
13.2 Member name lookup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
13.3 Virtual functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
13.4 Abstract classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265
14 Member access control 267
14.1 Access specifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
14.2 Accessibility of base classes and base class members . . . . . . . . . . . . . . . . . . . . . . 269
14.3 Friends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272
14.4 Protected member access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
14.5 Access to virtual functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
14.6 Multiple access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
14.7 Nested classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
15 Special member functions 278
15.1 Constructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
15.2 Temporary objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
15.3 Conversions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
15.4 Destructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
15.5 Free store . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
15.6 Initialization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
15.7 Construction and destruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
15.8 Copying and moving class objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
16 Overloading 309
16.1 Overloadable declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
16.2 Declaration matching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
16.3 Overload resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
Contents ©ISO/IEC 2017 – All rights reserved v

16.4 Address of overloaded function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333
16.5 Overloaded operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 334
16.6 Built-in operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 339
17 Templates 342
17.1 Template parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
17.2 Names of template specializations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
17.3 Template arguments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 348
17.4 Type equivalence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 354
17.5 Template declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
17.6 Name resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 373
17.7 Template instantiation and specialization . . . . . . . . . . . . . . . . . . . . . . . . . . . 388
17.8 Function template specializations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
17.9 Deduction guides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 421
18 Exception handling 422
18.1 Throwing an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
18.2 Constructors and destructors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
18.3 Handling an exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 425
18.4 Exception specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 427
18.5 Special functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430
19 Preprocessing directives 432
19.1 Conditional inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433
19.2 Source file inclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
19.3 Macro replacement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 436
19.4 Line control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 441
19.5 Error directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.6 Pragma directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.7 Null directive . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.8 Predefined macro names . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
19.9 Pragma operator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444
20 Library introduction 445
20.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 445
20.2 The C standard library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
20.3 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
20.4 Method of description (Informative) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449
20.5 Library-wide requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
21 Language support library 476
21.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
21.2 Common definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 476
21.3 Implementation properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 481
21.4 Integer types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 490
21.5 Start and termination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 491
21.6 Dynamic memory management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 492
21.7 Type identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 500
21.8 Exception handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 502
21.9 Initializer lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 507
21.10 Other runtime support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 508
Contents ©ISO/IEC 2017 – All rights reserved vi

22 Diagnostics library 511
22.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
22.2 Exception classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 511
22.3 Assertions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
22.4 Error numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515
22.5 System error support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 517
23 General utilities library 528
23.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
23.2 Utility components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 528
23.3 Compile-time integer sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 536
23.4 Pairs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 537
23.5 Tuples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 541
23.6 Optional objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 553
23.7 Variants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567
23.8 Storage for any type . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 580
23.9 Bitsets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 586
23.10 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 592
23.11 Smart pointers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607
23.12 Memory resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 634
23.13 Class template scoped_allocator_adaptor . . . . . . . . . . . . . . . . . . . . . . . . . . 645
23.14 Function objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 651
23.15 Metaprogramming and type traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675
23.16 Compile-time rational arithmetic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 699
23.17 Time utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 702
23.18 Class type_index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 719
23.19 Execution policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 720
24 Strings library 723
24.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723
24.2 Character traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 723
24.3 String classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 729
24.4 String view classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 762
24.5 Null-terminated sequence utilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 772
25 Localization library 778
25.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
25.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 778
25.3 Locales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 780
25.4 Standard locale categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 787
25.5 C library locales . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 825
26 Containers library 826
26.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
26.2 Container requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 826
26.3 Sequence containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 864
26.4 Associative containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896
26.5 Unordered associative containers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 918
26.6 Container adaptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 942
Contents ©ISO/IEC 2017 – All rights reserved vii

27 Iterators library 952
27.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
27.2 Iterator requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 952
27.3 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 958
27.4 Iterator primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 961
27.5 Iterator adaptors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 964
27.6 Stream iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 977
27.7 Range access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 984
27.8 Container access . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 985
28 Algorithms library 986
28.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 986
28.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 986
28.3 Algorithms requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1005
28.4 Parallel algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1006
28.5 Non-modifying sequence operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1009
28.6 Mutating sequence operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1017
28.7 Sorting and related operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1027
28.8 C library algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1046
29 Numerics library 1047
29.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
29.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
29.3 Numeric type requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1047
29.4 The floating-point environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1048
29.5 Complex numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1049
29.6 Random number generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1059
29.7 Numeric arrays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1102
29.8 Generalized numeric operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1122
29.9 Mathematical functions for floating-point types . . . . . . . . . . . . . . . . . . . . . . . . 1136
30 Input/output library 1153
30.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1153
30.2 Iostreams requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154
30.3 Forward declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1154
30.4 Standard iostream objects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1156
30.5 Iostreams base classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1158
30.6 Stream buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1175
30.7 Formatting and manipulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1184
30.8 String-based streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1211
30.9 File-based streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1221
30.10 File systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1235
30.11 C library files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1288
31 Regular expressions library 1292
31.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1292
31.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1292
31.3 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1293
31.4 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1295
31.5 Namespace std::regex_constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1301
31.6 Class regex_error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1304
Contents ©ISO/IEC 2017 – All rights reserved viii

31.7 Class template regex_traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1305
31.8 Class template basic_regex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1307
31.9 Class template sub_match . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1313
31.10 Class template match_results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1318
31.11 Regular expression algorithms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1324
31.12 Regular expression iterators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1329
31.13 Modified ECMAScript regular expression grammar . . . . . . . . . . . . . . . . . . . . . . 1335
32 Atomic operations library 1338
32.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1338
32.2 Header synopsis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1338
32.3 Type aliases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
32.4 Order and consistency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1342
32.5 Lock-free property . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1344
32.6 Class template atomic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1345
32.7 Non-member functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1352
32.8 Flag type and operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1352
32.9 Fences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1353
33 Thread support library 1355
33.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
33.2 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1355
33.3 Threads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1358
33.4 Mutual exclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1363
33.5 Condition variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1384
33.6 Futures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1391
A Grammar summary 1408
A.1 Keywords . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1408
A.2 Lexical conventions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1408
A.3 Basic concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1413
A.4 Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1413
A.5 Statements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1417
A.6 Declarations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1418
A.7 Declarators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1422
A.8 Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1424
A.9 Derived classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1425
A.10 Special member functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426
A.11 Overloading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426
A.12 Templates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1426
A.13 Exception handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1427
A.14 Preprocessing directives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1428
B Implementation quantities 1430
C Compatibility 1432
++
C.1 C and ISO C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1432
++ ++
C.2 C and ISO C 2003 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1441
++ ++
C.3 C and ISO C 2011 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1447
++ ++
C.4 C and ISO C 2014 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1449
C.5 C standard library . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1453
Contents ©ISO/IEC 2017 – All rights reserved ix

D Compatibility features 1456
D.1 Redeclaration of static constexpr data members . . . . . . . . . . . . . . . . . . . . . . 1456
D.2 Implicit declaration of copy functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1456
D.3 Deprecated exception specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1456
++
D.4 C standard library headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1456
D.5 C standard library headers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457
D.6 char* streams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1457
D.7 uncaught_exception . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1466
D.8 Old adaptable function bindings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1466
D.9 The default allocator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1471
D.10 Raw storage iterator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1472
D.11 Temporary buffers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1473
D.12 Deprecated type traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1474
D.13 Deprecated iterator primitives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1475
D.14 Deprecated shared_ptr observers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1475
D.15 Deprecated standard code conversion facets . . . . . . . . . . . . . . . . . . . . . . . . . . 1475
D.16 Deprecated convenience conversion interfaces . . . . . . . . . . . . . . . . . . . . . . . . . 1477
Bibliography 1482
Cross references 1483
++
Cross references from ISO C 2014 1504
Index 1506
Index of grammar productions 1539
Index of library names 1543
Index of implementation-defined behavior 1601
Contents ©ISO/IEC 2017 – All rights reserved x

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has
been established has the right to be represented on that committee. International organizations, governmental
and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
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 ISO documents 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 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).
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 ex-
pressions 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 the following URL:
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/IEC JTC 1, Information technology, Subcommittee
SC 22, Programming languages, their environments and system software interfaces.
This fifth edition cancels and replaces the fourth edition (ISO/IEC 14882:2014), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— expression evaluation order is specified in more cases
— removal of trigraphs
— adjustments to value categories resulting in copy elision being mandatory
— additional character and floating point literal syntaxes
— lambda expressions extended to permit capture of *this and use in constant expressions
— initializer statements for if and switch statements
— addition of constexpr if statements
— range-based for statement generalized to support heterogeneous begin and end types
— addition of structured bindings
— addition of inline variables
— list initialization extended to support enumerations and aggregates with base classes
— message in static_assert is now optional
— addition of nested namespace definition syntax
Foreword ©ISO/IEC 2017 – All rights reserved xi

— extended support for attributes
— exception specifications are now part of function types
— template argument deduction is now supported for class templates
— addition of fold expressions
— pack expansion can be performed on using declarations
— permitted forms of template parameters and template arguments have been generalized
— dynamic allocation is supported for over-aligned types
— preprocessor can detect presence of header files with __has_include
— new utility functions, types, and templates in the standard library, including
— an any type
— an optional class template
— a variant class template
— a clamp function
— a std::byte type
— a not_fn function
— a void_t alias template
— conjunction, disjunction, and negation templates
— an invoke function, and is_invocable and invoke_result type traits
— an is_swappable type trait
— extended constant expression evaluation support in the standard library
— elementary conversion functions between strings and numeric types added
— constructors for pair and tuple are conditionally-explicit
— shared_ptrs of array types now supported
— additional algorithms for managing uninitialized memory
— addition of polymorphic memory resources
— addition of substring search facilities providing the Boyer-Moore and Boyer-Moore-Horspool search
algorithms
— addition of variable templates for type traits
— addition of a non-owning string view template
— ability to splice elements between containers for maps and sets
— better support for element insertion in unique-key maps
— support for incomplete types in containers
— addition of parallel algorithms
— addition of sample algorithm
— addition of mathematical special functions, and gcd, lcm, and three-argument hypot functions
— addition of support for operations on file systems
— addition of shared mutexes and variadic lock guards
— removal of deprecated features
Foreword ©ISO/IEC 2017 – All rights reserved xii

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.
++
C is a general purpose programming language based on the C programming language as described in
ISO/IEC 9899:2011 Programming languages — C (hereinafter referred to as the C standard). In addition to
++
the facilities provided by C, C provides additional data types, classes, templates, exceptions, namespaces,
operator overloading, function name overloading, references, free store management operators, and additional
library facilities.
Scope ©ISO/IEC 2017 – 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)
— Ecma International, ECMAScript Language Specification, Standard Ecma-262, third edition, 1999.
(1.2)
— ISO/IEC 2382 (all parts), Information technology — Vocabulary
(1.3)
— ISO/IEC 9899:2011, Programming languages — C
(1.4)
— ISO/IEC 9945:2003, Information Technology — Portable Operating System Interface (POSIX)
(1.5)
— ISO/IEC 10646-1:1993, Information technology — Universal Multiple-Octet Coded Character Set (UCS)
— Part 1: Architecture and Basic Multilingual Plane
(1.6)
— ISO/IEC/IEEE 60559:2011, Information technology — Microprocessor Systems — Floating-Point
arithmetic
(1.7)
— ISO 80000-2:2009, Quantities and units — Part 2: Mathematical signs and symbols to be used in the
natural sciences and technology
The library described in Clause 7 of ISO/IEC 9899:2011 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.
++
1) With the qualifications noted in Clauses 21 through 33 and in C.5, the C standard library is a subset of the C standard
library.
Normative references ©ISO/IEC 2017 – All rights reserved 2

3 Terms and definitions [intro.defs]
For the purposes of this document, the terms and definitions given in ISO/IEC 2382-1:1993, the terms,
definitions, and symbols given in ISO 80000-2:2009, and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
(2.1)
— ISO Online browsing platform: available at http://www.iso.org/obp
(2.2)
— IEC Electropedia: available at http://www.electropedia.org/
20.3 defines additional terms that are used only in Clauses 20 through 33 and Annex D.
Terms that are used only in a small portion of this document are defined where they are used and italicized
where they are defined.
3.1 [defns.access]
access
〈execution-time action〉 read or modify the value of an object
3.2 [defns.argument]
argument
〈function call expression〉 expression in the comma-separated list bounded by the parentheses (8.2.2)
3.3 [defns.argument.macro]
argument
〈function-like macro〉 sequence of preprocessing tokens in the comma-separated list bounded by the parenthe-
ses (19.3)
3.4 [defns.argument.throw]
argument
〈throw expression〉 operand of throw (8.17)
3.5 [defns.argument.templ]
argument
〈template instantiation〉 constant-expression, type-id, or id-expression in the comma-separated list bounded
by the angle brackets (17.3)
3.6 [defns.block]
block
wait for some condition (other than for the implementation to execute the execution steps of the thread of
execution) to be satisfied before continuing execution past the blocking operation
3.7 [defns.cond.supp]
conditionally-supported
program construct that an implementation is not required to support
[Note 1 to entry: Each implementation documents all conditionally-supported constructs that it does not
support. —end note]
3.8 [defns.diagnostic]
diagnostic message
message belonging to an implementation-defined subset of the implementation’s output messages
§ 3.8 ©ISO/IEC 2017 – All rights reserved 3

3.9 [defns.dynamic.type]
dynamic type
〈glvalue〉 type of the most derived object (4.5) to which the glvalue refers
[Example: If a pointer (11.3.1) p whose static type is “pointer to class B” is pointing to an object of class D,
derived from B (Clause 13), the dynamic type of the expression *p is “D”. References (11.3.2) are treated
similarly. —end example]
3.10 [defns.dynamic.type.prvalue]
dynamic type
〈prvalue〉 static type of the prvalue expression
3.11 [defns.ill.formed]
ill-formed program
program that is not well-formed (3.29)
3.12 [defns.impl.defined]
implementation-defined behavior
behavior, for a well-formed program construct and correct data, that depen
...