ISO/IEC TR 19769:2004

Information technology — Programming languages, their environments and system software inferfaces — Extensions for the programming language C to support new character data types

ISO/IEC TR 19769:2004 specifies two extended character data types as an extension to the programming language C, specified by ISO/IEC 9899.

Technologies de l'information — Langages de programmation, leurs environnements et interfaces de logiciel système — Extensions pour que le langage de programmation C supporte des types de données de caractères nouveaux

General Information

• Status: Withdrawn
• Publication Date: 19-Jul-2004
• Withdrawal Date: 19-Jul-2004
• 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 14 - C
• Current Stage: 9599 - Withdrawal of International Standard
• Completion Date: 17-Aug-2016

Standards Content (Sample)

TECHNICAL ISO/IEC
REPORT TR
19769
First edition
2004-07-15

Information technology — Programming
languages, their environments and
system software interfaces — Extensions
for the programming language C to
support new character data types
Technologies de l'information — Langages de programmation, leurs
environnements et interfaces de logiciel système — Extensions pour
que le langage de programmation C supporte des types de données de
caractères nouveaux




Reference number
ISO/IEC TR 19769:2004(E)
©
ISO/IEC 2004

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ISO/IEC TR 19769:2004(E)
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ii © ISO/IEC 2004 – All rights reserved

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ISO/IEC TR 19769:2004(E)




Contents                                                                Page

Foreword. iv
Introduction. v
1 Scope. 1
2 Normative references. 1
3 The new typedefs . 2
4 Encoding . 3
5 String literals and character constants. 4
5.1 String literals and character constants notations. 4
5.2 The string concatenation. 4
6 Library functions. 5
6.1 The mbrtoc16 function . 5
6.2 The c16rtomb function . 6
6.3 The mbrtoc32 function . 7
6.4 The c32rtomb function . 8
7 ANNEX A Unicode encoding forms: UTF-16, UTF-32 . 9

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ISO/IEC TR 19769:2004(E)
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. In the field of information
technology, ISO and IEC have established a joint technical committee, ISO/IEC JTC 1.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of the joint technical committee is to prepare International Standards. Draft International
Standards adopted by the joint technical committee are circulated to national bodies for voting. Publication as
an International Standard requires approval by at least 75 % of the national bodies casting a vote.
In exceptional circumstances, the joint technical committee may propose the publication of a Technical Report
of one of the following types:
— type 1, when the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts;
— type 2, when the subject is still under technical development or where for any other reason there is the
future but not immediate possibility of an agreement on an International Standard;
— type 3, when the joint technical committee has collected data of a different kind from that which is
normally published as an International Standard (“state of the art”, for example).
Technical Reports of types 1 and 2 are subject to review within three years of publication, to decide whether
they can be transformed into International Standards. Technical Reports of type 3 do not necessarily have to
be reviewed until the data they provide are considered to be no longer valid or useful.
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.
ISO/IEC TR 19769, which is a Technical Report of type 2, was prepared by Joint Technical Committee
ISO/IEC JTC 1, Information technology, Subcommittee SC 22, Programming languages, their environments
and system software interfaces.

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ISO/IEC TR 19769:2004(E)
Introduction

The C language has evolved over the last decades, various code pages and multibyte
libraries have been introduced, and extended character set support has been
introduced; however, the support for extended character data types in the C language
is still limited.  Today, the introduction and the success of the Unicode/ISO10646
standard and of its implementation in modern computer languages create ever
increasing demands on the C language to give Unicode/ISO10646 better support.
This paper addresses the introduction of new extended character data types in the C
language in order to support future character encoding forms, including
Unicode/ISO10646.

The Unicode standard supports 3 encoding forms:

• UTF-8
• UTF-16
• UTF-32

Each encoding form has advantages and disadvantages, so the choice of the encoding
form should be left to the application. Currently, some C applications implement
UTF-8 using char type, UTF-16 using unsigned short or wchar_t, and UTF-32
using unsigned long or wchar_t. The current situation, however, faces the
following major problems:

• The size of wchar_t is implementation defined. While wchar_t offers a
form of platform portability for C applications, Unicode offers the possibility
to write platform independent applications using a platform independent data
format.
• There is no string literal for 16- or 32-bit based integer types, but the Unicode
encoding forms require string literals.

It is sensible to give all the Unicode encoding forms appropriate data type support.
UTF-8 is normally considered as the preferred multibyte encoding, for sequences of
one or more elements of type char. This paper suggests the implementation of 16
and 32 bit character data types: char16_t and char32_t. The new data types
guarantee program portability through clearly defined character widths. The
encoding of the new data types should be as generic as possible in order to support
not only Unicode but also other character encodings.

It is generally desirable that C applications process entire strings at once rather than
process individual characters in isolation. This paper does not specify the detail of
library functions for the new data types, except one set of character conversion
functions.
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TECHNICAL REPORT ISO/IEC TR 19769:2004(E)

Information technology — Programming languages, their
environments and system software interfaces — Extensions for
the programming language C to support new character data
types
1 Scope

This Technical Report specifies two extended character data types as an extension to the
programming language C, specified by the international standard ISO/IEC 9899:1999.

2 Normative references

The following referenced documents are indispensable for the application 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.

ISO/IEC 9899:1999, Programming Languages – C

ISO/IEC 10646-1:2000, Information technology – Universal multiple-octet coded character
set (UCS) – Part 1: Architecture and Basic Multilingual Plane

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ISO/IEC TR 19769:2004(E)
3 The new typedefs

This Technical Report introduces the following two new typedefs, char16_t and
char32_t :

typedef T1 char16_t;
typedef T2 char32_t;

where T1 has the same type as uint_least16_t and T2 has the same type as
uint_least32_t.

The new typedefs guarantee certain widths for the data types, whereas the width of
wchar_t is implementation defined. The data values are unsigned, while char and
wchar_t could take signed values.

This Technical Report also introduces the new header:



The new typedefs, char16_t and char32_t, are defined in

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ISO/IEC TR 19769:2004(E)
4 Encoding

C99 subclause 6.10.8 specifies that the value of the macro _ _STDC_ISO_10646_ _
shall be "an integer constant of the form yyyymmL (for example, 199712L), intended
to indicate that values of type wchar_t are the coded representations of the
characters defined by ISO/IEC 10
...