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Character sets and encodings

This page describes several character sets specified by the C++ standard.

Translation character set

The translation character set consists of the following elements:

each abstract character assigned a code point in the Unicode codespace, and
a distinct character for each Unicode scalar value not assigned to an abstract character.

The translation character set is a superset of the basic character set and the basic literal character set (see below).

(since C++23)

Basic character set

The basic character set consists of the following 96 (until C++26)99 (since C++26) characters:

Code unit	Character	Glyph
U+0009	Character tabulation
U+000B	Line tabulation
U+000C	Form feed (FF)
U+0020	Space
U+000A	Line feed (LF)	new-line
U+0021	Exclamation mark	`!`
U+0022	Quotation mark	`"`
U+0023	Number sign	`#`
U+0025	Percent sign	`%`
U+0026	Ampersand	`&`
U+0027	Apostrophe	`'`
U+0028	Left parenthesis	`(`
U+0029	Right parenthesis	`)`
U+002A	Asterisk	`*`
U+002B	Plus sign	`+`
U+002C	Comma	`,`
U+002D	Hyphen-minus	`-`
U+002E	Full stop	`.`
U+002F	Solidus	`/`
U+0030 .. U+0039	Digit zero .. nine	`0 1 2 3 4 5 6 7 8 9`
U+003A	Colon	`:`
U+003B	Semicolon	`;`
U+003C	Less-than sign	`<`
U+003D	Equals sign	`=`
U+003E	Greater-than sign	`>`
U+003F	Question mark	`?`
U+0041 .. U+005A	Latin capital letter A .. Z	`A B C D E F G H I J K L M` `N O P Q R S T U V W X Y Z`.
U+005B	Left square bracket	`[`
U+005C	Reverse solidus	`\`
U+005D	Right square bracket	`]`
U+005E	Circumflex accent	`^`
U+005F	Low line	`_`
U+0061 .. U+007A	Latin small letter a .. z	`a b c d e f g h i j k l m` `n o p q r s t u v w x y z`.
U+007B	Left curly bracket	`{`
U+007C	Vertical line	`\|`
U+007D	Right curly bracket	`}`
U+007E	Tilde	`~`

The following characters are added to the basic character set since C++26:

Code unit	Character	Glyph
U+0024	Dollar Sign	`$`
U+0040	Commercial At	`@`
U+0060	Grave Accent	`

(since C++26)

Basic literal character set

The basic literal character set consists of all characters of the basic character set, plus the following control characters:

Code unit	Character
U+0000	Null
U+0007	Bell
U+0008	Backspace
U+000D	Carriage return (CR)

Execution character set

The execution character set and the execution wide-character set are supersets of the basic literal character set. The encodings of the execution character sets and the sets of additional elements (if any) are locale-specific. Each element of execution wide-character set must be representable as a distinct wchar_t code unit.

Code unit and literal encoding

A code unit is an integer value of character type. Characters in a character literal other than a multicharacter or non-encodable character literal or in a string literal are encoded as a sequence of one or more code units, as determined by the encoding prefix; this is termed the respective literal encoding.

A literal encoding or a locale-specific encoding of one of the execution character sets encodes each element of the basic literal character set as a single code unit with non-negative value, distinct from the code unit for any other such element. A character not in the basic literal character set can be encoded with more than one code unit; the value of such a code unit can be the same as that of a code unit for an element of the basic literal character set. The encodings of the execution character sets can be unrelated to any literal encoding.

The ordinary literal encoding is the encoding applied to an ordinary character or string literal. The wide literal encoding is the encoding applied to a wide character or string literal.

The U+0000 NULL character is encoded as the value 0. No other element of the translation character set is encoded with a code unit of value 0. The code unit value of each decimal digit character after the digit 0 (U+0030) shall be one greater than the value of the previous. The ordinary and wide literal encodings are otherwise implementation-defined.

For a UTF-8, UTF-16, or UTF-32 literal, the UCS scalar value corresponding to each character of the translation character set is encoded as specified in ISO/IEC 10646 for the respective UCS encoding form.

Notes

The standard names of some character sets are changed in C++23 via P2314R4.

New name(s)	Old name(s)
basic character set	basic source character set
basic literal character set	basic execution character set basic execution wide-character set

Mapping from source file (other than a UTF-8 source file) (since C++23) characters to the basic character set (until C++23)translation character set (since C++23) during translation phase 1 is implementation-defined, so an implementation is required to document how the basic source characters are represented in source files.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
CWG 788	C++98	the values of the members of the execution character sets were implementation-defined, but were not locale-specific	they are locale-specific
CWG 1796	C++98	the representation of the null (wide) character in basic execution (wide-)character set had all zero bits	only required value to be zero