[lex.ccon] (original) (raw)
5 Lexical conventions [lex]
5.13 Literals [lex.literal]
5.13.3 Character literals [lex.ccon]
character-literal: encoding-prefix ' c-char-sequence '
encoding-prefix: one of u8 u U L
c-char-sequence: c-char c-char-sequence c-char
c-char: any member of the basic source character set except the single-quote ', backslash , or new-line character escape-sequence universal-character-name
escape-sequence: simple-escape-sequence octal-escape-sequence hexadecimal-escape-sequence
simple-escape-sequence: one of ' " ? \ \a \b \f \n \r \t \v
octal-escape-sequence: \ octal-digit \ octal-digit octal-digit \ octal-digit octal-digit octal-digit
hexadecimal-escape-sequence: \x hexadecimal-digit hexadecimal-escape-sequence hexadecimal-digit
A character-literal that does not begin withu8, u, U, or Lis an ordinary character literal.
An ordinary character literal that contains a single c-char representable in the execution character set has type char, with value equal to the numerical value of the encoding of the c-char in the execution character set.
An ordinary character literal that contains more than one c-char is amulticharacter literal.
A multicharacter literal, or an ordinary character literal containing a single c-char not representable in the execution character set, is conditionally-supported, has type int,and has an implementation-defined value.
A character-literal that begins with u8, such as u8'w',is a character-literal of type char8_t, known as a UTF-8 character literal.
The value of a UTF-8 character literal is equal to its ISO/IEC 10646 code point value, provided that the code point value can be encoded as a single UTF-8 code unit.
[ Note
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That is, provided the code point value is in the range (hexadecimal).
— end note
]
If the value is not representable with a single UTF-8 code unit, the program is ill-formed.
A UTF-8 character literal containing multiple c-chars is ill-formed.
A character-literal that begins with the letter u, such as u'x',is a character-literal of type char16_t, known as a UTF-16 character literal.
The value of a UTF-16 character literal is equal to its ISO/IEC 10646 code point value, provided that the code point value is representable with a single 16-bit code unit.
[ Note
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That is, provided the code point value is in the range (hexadecimal).
— end note
]
If the value is not representable with a single 16-bit code unit, the program is ill-formed.
A UTF-16 character literal containing multiple c-chars is ill-formed.
A character-literal that begins with the letter U, such as U'y',is a character-literal of type char32_t, known as a UTF-32 character literal.
The value of a UTF-32 character literal containing a single c-char is equal to its ISO/IEC 10646 code point value.
A UTF-32 character literal containing multiple c-chars is ill-formed.
A character-literal that begins with the letter L, such as L'z',is a wide-character literal.
A wide-character literal has typewchar_t.17
The value of a wide-character literal containing a singlec-char has value equal to the numerical value of the encoding of the c-char in the execution wide-character set, unless thec-char has no representation in the execution wide-character set, in which case the value is implementation-defined.
[ Note
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The type wchar_t is able to represent all members of the execution wide-character set (see [basic.fundamental]).
— end note
]
The value of a wide-character literal containing multiple c-chars isimplementation-defined.
Certain non-graphic characters, the single quote ', the double quote ", the question mark ?,18and the backslash\, can be represented according to Table 9.
The double quote " and the question mark ?, can be represented as themselves or by the escape sequences\" and \? respectively, but the single quote ' and the backslash \shall be represented by the escape sequences \' and\\ respectively.
Escape sequences in which the character following the backslash is not listed in Table 9 are conditionally-supported, with implementation-defined semantics.
An escape sequence specifies a single character.
Table 9: Escape sequences [tab:lex.ccon.esc]
| new-line | NL(LF) | \n |
|---|---|---|
| horizontal tab | HT | \t |
| vertical tab | VT | \v |
| backspace | BS | \b |
| carriage return | CR | \r |
| form feed | FF | \f |
| alert | BEL | \a |
| backslash | \ | \\ |
| question mark | ? | \? |
| single quote | ' | \' |
| double quote | " | \" |
| octal number | ooo | \ooo |
| hex number | hhh | \xhhh |
The escape\ooo consists of the backslash followed by one, two, or three octal digits that are taken to specify the value of the desired character.
The escape\xhhhconsists of the backslash followed by x followed by one or more hexadecimal digits that are taken to specify the value of the desired character.
There is no limit to the number of digits in a hexadecimal sequence.
A sequence of octal or hexadecimal digits is terminated by the first character that is not an octal digit or a hexadecimal digit, respectively.
The value of a character-literal is implementation-defined if it falls outside of the implementation-defined range defined for char (for character-literals with no prefix) orwchar_t (for character-literals prefixed by L).
[ Note
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If the value of a character-literal prefixed byu, u8, or Uis outside the range defined for its type, the program is ill-formed.
— end note
]
A universal-character-name is translated to the encoding, in the appropriate execution character set, of the character named.
If there is no such encoding, the universal-character-name is translated to animplementation-defined encoding.
[ Note
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In translation phase 1, a universal-character-name is introduced whenever an actual extended character is encountered in the source text.
However, the actual compiler implementation may use its own native character set, so long as the same results are obtained.
— end note
]