ILE C/C++ Language Reference

The Unicode Standard

The Unicode Standard is the specification of an encoding scheme for written characters and text. It is a universal standard that enables consistent encoding of multilingual text and allows text data to be interchanged internationally without conflict. The ISO standards for C and C++ refer to ISO/IEC 10646-1:2000, Information Technology--Universal Multiple-Octet Coded Character Set (UCS). (The term octet is used by ISO to refer to a byte.) The ISO/IEC 10646 standard is more restrictive than the Unicode Standard in the number of encoding forms: a character set that conforms to ISO/IEC 10646 is also conformant to the Unicode Standard.

The Unicode Standard specifies a unique numeric value and name for each character and defines three encoding forms for the bit representation of the numeric value. The name/value pair creates an identity for a character. The hexadecimal value representing a character is called a code point. The specification also describes overall character properties, such as case, directionality, alphabetic properties, and other semantic information for each character. Modeled on ASCII, the Unicode Standard treats alphabetic characters, ideographic characters, and symbols, and allows implementation-defined character codes in reserved code point ranges. The encoding scheme of the Unicode Standard is therefore sufficiently flexible to handle all known character encoding requirements, including coverage of historical scripts from any country in the world.

C++ allows the universal character name construct defined in ISO/IEC 10646 to represent characters outside the basic source character set. The universal character name is permitted in identifiers, character constants, and string literals. This language feature is independent of the language level specified at compile time.

The following table shows the generic universal character name construct and how it corresponds to the ISO/IEC 10646 short name.

Universal character name ISO/IEC 10646 short name
\UNNNNNNNN NNNNNNNN
\uNNNN 0000NNNN
where N is a hexadecimal digit

C++ disallows the hexadecimal values representing characters in the base source code set and the code points reserved by ISO/IEC 10646 for control characters. The following characters are also disallowed:

Related References


[ Top of Page | Previous Page | Next Page | Table of Contents | Index ]